INTERNAL - WORKS



ELECTRIFICATIONS WORK - INTERNAL

16.1. General and commercial-Scope

(i) These general specifications indicate the requirements and precautions to be taken during the execution of Internal Electrical Installation works to ensure efficient, safe, economical and practical use of materials and equipment’s including prevention of risks and fire hazards.

ii) These general specifications are subject to revision from time to time.

iii)  This section covers the general commercial requirements applicable to works contracts for Internal Electrical Installation works, in cases where tenders are called for and work is executed as contract basis

16.1.1. Related documents.

(i)  Each work has its own particular requirements.  These general specifications shall be read in conjunction with the standard conditions of contract contained in contract forms concerned, and their correction slips, the tender specifications, schedule of work, drawings and other documents in the tender papers connected with the particular work. 

(ii)  In the event of any discrepancy between these general specifications and the Inter-connected documents, the requirements and conditions as per the latter shall have overriding value and shall be followed.

16.1.2 Submission of tenders

(i) The tender shall be submitted complete with the following:-

a) Complete tender documents as purchased and duly filled in and signed.  The price part of the tender shall be indicated only on the tender schedule of work.

b) Earnest money deposit in one of the acceptable forms as specified.

c) Any other supplementary details required for the evaluation of the tenders such as drawings, technical literature/ catalogues, data etc.

d) Deviations, if any, from tender specifications and/or tender conditions, with reasons therefore.  It is open to the department whether or not to accept them.

ii) Where two part tendering system is proposed to be adopted in any particular work, the procedure for submission and opening of tenders shall be indicated in tender documents for that work.

16.1.3 Rates

i) The work shall be treated as on works contract basis and the rates tendered shall be for complete items of work inclusive of all taxes (including works contract tax, if any), duties, and levies etc. and all charges for items contingent to the work, such as, packing, forwarding, insurance, freight and delivery at site for the materials to be supplied by the contractor watch and ward of all materials for the Internal E.I work at site etc.

ii) Prices quoted shall be firm. Price adjustments shall however be governed by the price adjustment clause of the conditions of contract.

16.1.4 Taxes and Duties

i) Being an indivisible works contract, sales tax, excise duty etc. are not payable separately.

ii) Octroi duty shall not be paid separately for the materials supplied by the contractor, but octroi exemption certificates can be furnished by the department, on demand.  However, the department is not liable to reimburse the octroi duty in case such exemption certificates are not honoured by the concerned authorities. 

16.1.5 Mobilisation advance - Mobilisation advance shall be paid for the work, if so specified in the conditions of contract

16.1.6 Completeness of tender - All sundry fittings, assemblies, accessories, hardware items, foundation bolts, termination lugs for electrical connections as required, and all other sundry items which are useful and necessary for proper assembly and efficient working of the various components of the work shall be deemed to have been included in the tender, whether such items are specifically mentioned in the tender documents or not. 

16.1.7 Works to be arranged by the department - Unless and otherwise specified in the tender documents, the following works shall be arranged by the department:

i) Storage space for all equipment, components and materials for the work.

ii) Supply of materials to the contractor as stipulated in the tender documents.

16.1.8 Works to be done by the contractor - Unless and otherwise mentioned in the tender documents, the following works shall be done by the contractor, and therefore their cost shall be deemed to be included in their tendered cost: -

i) Foundations for equipments and components where required, including foundation bolts.

ii) Cutting and making good all damages caused during installation and restoring the same to their original finish.

iii) Sealing of all floor openings provided by him for pipes and cables, from fire safety point of view, after laying of the same.

iv) Painting at site of all exposed metal surfaces of the installation other than pre-painted items like fittings, fans, switch gear/distribution gear items, cubical switch board etc.  Damages to finished surfaces of these items while handling and erection shall however be rectified to the satisfaction of the engineer-in-charge. 

v) Temporary shed if required over the storage space and locking arrangement thereof, and watch and ward of the materials and completed installation till completion of the work.

vi) Water and power as may be required for installation and testing.

vii) Testing and commissioning of completed installation.

16.1.9 Storage and custody of materials - Suitable and lockable storage accommodation shall be provided by the department free of cost to the contractor.  However, their proper storage and safe custody shall be responsibility till the final taking over of the installations by the department.

16.1.10 Electric power supply and water supply - Unless and otherwise specified, power supply and water supply as may be required shall be arranged by the contractor for installation and testing of the equipments at the site of work.

16.1.11 Tools for handling and erection - All tools and tackles required for handling of equipment’s and materials at site of work as well as for their assembly and erection and also necessary test instruments shall be the responsibility of the contractor.

16.1.12 Co-ordination with other agencies - The contractor shall co-ordinate with all other agencies involved in the building work so that the building work is not hampered due to delay in his work.  Recessed conduit and other works, which directly affect the progress of building work, should be given priority.

16.1.13 Care shall be taken by the contractor to avoid damage tot he building during execution of his part of the work.  He shall be responsible for repairing all damages and restoring the same to their original finish at his cost.  He shall also remove at his cost all unwanted and waste materials arising out of his work from the site. 

16.1.14. Structural alterations to buildings

i) No structural member in the building shall be damaged / altered, without prior approval from the competent authority through the engineer.

ii) Structural provisions like openings, cutouts, if nay, provided by the department for the work, shall be used.  Where these require modifications, or where fresh provisions are required to be made, such contingent works shall be carried out by the contractor at his cost. 

iii) All such openings in floors provided by the department shall be closed by the contractor after installing the cables/conduits/rising mains etc, as the case may be, by any suitable means as approved by the engineer without any extra payment.

iv) All chases required in connection with the electrical works shall be provided and filled by the contractor at his own cost tot he original architectural finish of the buildings. 

16.1.15 Work in occupied buildings

i) When work is executed in occupied buildings, there should be minimum of inconvenience to the occupants.  The work shall be programmed in consultation with the engineer and the occupying department.  If so required, the work may have to be done even before and after office hours.

ii) The contractor shall be responsible to abide by the regulations or restrictions set in regard to entry into, and movement within the premises. 

iii) The contractor shall not tamper with any of the existing installations including their switching operations or connections there to without specific approval from the engineer.

General and Technical - Scope - This section covers the general technical requirements and measurement of the various components in Internal Electrical Installation works.

16.2.1 Terminology

16.2.1.1 The definition of terms shall be in accordance with IS: 732-1989 (Indian Standard Code of Practice for Electrical Wiring), except for the definitions of point, circuit, and submain wiring, which are defined in clauses 2.2.1, 2.3.1 and 2.3.2 hereunder

16.2.2. SPECIFICATIONS for point wiring

16.2.2.1 Definition - A point (other than socket outlet point) shall include all work necessary in complete wiring to the following outlets from the controlling switch or MCB.  The scope of wiring for a point shall, however, include the wiring work necessary in tapping from another point in the same distribution circuit. 

  1. Ceiling rose or connector (in the case of points for ceiling/exhaust fan points, prewired light fittings, and call bells).
  2. Ceiling rose (in the case of pendants except stiff pendants).
  3. Back plate (in the case of stiff pendants).
  4. Lamp holder (in the case of goose neck type wall brackets, batten holders and fittings which are not pre-wired).

Note – In the case of call bell points, the words “from the controlling switch or MCB shall be read as from the ceiling rose meant for connection to bell push"

16.2.2.2 Scope - Following shall be deemed to be included in point wiring.

  1. Conduit/casing and capping/batten as the case may be, accessories for the same and wiring cables between the switch box and the point outlet. [See also (j) below].
  2. All fixing accessories such as clips, nails, screws, phil plug, rawl plug etc. as required.
  3. Mechanical protection of battens wiring upto 1.5 m from floor and at locations where wiring is liable to be damaged.
  4. Metal or PVC switch boxes for control switches, regulator, sockets etc, recessed or surface type, and phenolic laminated sheet covers over the same.
  5. Outlet boxes, junction boxes, pull-through boxes etc, but excluding metal boxes if any, provided with switchboards for loose wires/conduit terminations.
  6. Any special block required for neatly housing the connector in batten wiring system.
  7. Control switch or MCB, as specified.
  8. 3 pin or 6 pin socket, ceiling rose or connector as required. (2 pin and 5 pin socket outlet shall not be permitted).
  9. Connections to ceiling rose, connector, socket outlet, lamp holder, switch etc.
  10. Interconnecting wiring between points on the same circuit, in the same switch box or from another.
  11. Protective (loop earthing) conductor from one metallic switch box to another in the distribution circuits, and for socket out lets. (The length of protective conductor run along with the circuits / sub mains is excluded from the scope of points).
  12. Bushed conduit or porcelain tubing where wiring cables pass through wall etc.

16.2.2.3 Measurement

16.2.2.3.1 Point wiring (other than socket outlet points)

i) Unless and otherwise specified, there shall be no linear measurement for point wiring for light points, exhaust fan points and call bell points.  These shall be measured on unit basis by counting, and classified as laid down in 16.2.2.3.2. [see also clause 16.2.4(ii)]

ii) No separate measurement will be made for interconnections between points in the same distribution circuit and for the circuit protective (loop earthing) conductors between metallic switch boxes. 

16.2.2.3.2 Classification - Points measured under 16.2.2.3.1 on unit basis shall be classified as under according to the type of building.

i) Residential buildings  

  1. Group ‘A’, for point wiring for type I, type II and type III residential quarters and hostels.
  2. Group ‘B’, for point wiring for type IV and above types of residential quarters and barracks.

ii) Non-residential buildings -  Group ‘C’ for all types of non-residential buildings such as offices, hospitals, laboratories, educational institutions, libraries, etc.

iii) For any other type of building, the group under which the points are to be classified shall be decided by the concerned chief engineer (Electrical).

16.2.2.3.3 Point wiring for socket outlet points

i) The light plug (5A/6A) point wiring shall be measured on linear basis, from the respective tapping point of live cable, namely, switch box, another socket outlet point, or the sub distribution board as the case may be, upto the socket outlet

ii) The metal/PVC box with cover, switch/MCB, socket outlet and other accessories shall be measured and paid as a separate item.

Note – There shall normally be no “on the board” light plug point.

iii) The power point outlet may be 15A/5 A or 16A/6 A six pin socket outlet, where so specified in the tender documents.

16.2.2.3.4 Group control points wiring

i) In the case of points with more than one point controlled by the same switch, such points shall be measured in parts i.e.(a) from the switch to the first point outlet as one point and classified according to 16.2.2.3.2, and (b) for the subsequent points, the distance from that outlet to the next one and so on, shall be treated as separate point(s) and classified according to 16.2.2.3.2.

ii) No recovery shall be made for non-provision of more than one switch in such cases.

16.2.2.3.5 Twin control light points wiring

i) A light point controlled by two numbers of two way switches shall be measured as two points from the fitting to the switches on either side and classified according to 16.2.2.3.2.

ii) No recovery shall be made for non-provision of more than one ceiling rose or connector in such cases.

16.2.2.3.6 Multiple controlled call bell points wiring

i) In the case of call bell points with a single call bell outlet, controlled from more than one place, the pints shall be measured in parts i.e. (a) from the call bell outlet to one of the nearest ceiling roses meant for connection to bell push, treated as one point and classified according to 16.2.2.3.2 and, (b) from that ceiling rose to the next one and so on, shall be treated as separate point(s) and classified according to 16.2.2.3.2.

ii) No recovery shall be made for non-provision of more than one ceiling rose or connector for connection to call bell in such cases.

16.2.3 Circuit And Submain Wiring

16.2.3.1 Specifications for conduit wiring

Circuit wiring shall mean the wiring from the distribution board upto the tapping point for the nearest first point of that distribution circuit, viz. Upto the nearest first switch box.

16.2.3.2 Sub main wiring - Sub main wiring shall mean the wiring from one main/distribution switchboard to another.

16.2.3.3 Measurement of circuit and submain wiring

i) Circuit and submain wiring shall be measured on linear basis along the run of the wiring.  The measurement shall include all lengths from end to end of wood batten or conduit or casing and capping as the case may be, exclusive of interconnections inside the switchboards etc.  The increase on account of diversion or slackness shall not be included in the measurement.

ii) The length of circuit wiring with two wires shall be measured from the distribution board to the first nearest switch box in the circuit irrespective of whether the neutral conductor is taken to switch box or not.

iii) When wires of different circuits are grouped in a single conduit/casing and capping, the same shall be measured on linear basis depending on the actual number and sizes of wires run. 

iv) When circuit wires and wires of point wiring are run in the same conduit/casing and capping, circuit wiring shall be measured on linear basis depending on the actual number and sizes of wires run in the existing conduit/casing capping.

v) Protective (loop earthing) conductors, which are run along the circuit wiring and the sub main wiring, shall be measured on linear basis and paid for separately.

16.2.4 SPECIFICATIONS FOR OTHER WIRING WORKS

 Except as specified above for point wiring, circuit wiring and submain wiring, other types of wiring shall be measured separately on linear basis along the run of wiring depending on the actual number and sizes of wires run.

Rewiring - The scope of work of the rewiring items provided in the Schedule of Rates (Part I-Internal), 1994 includes only the replacement of wires.  Replacement of switches and other accessories shall be covered by the relevant and corresponding item in the Schedule.

16.2.5 Specifications for distribution wiring

16.2.5.1 Control at the point of entry of supply - There shall be a linked switch with fuse or circuit breaker on each live conductor of the supply mains at the point of entry.

16.2.5.2 Distribution

i) The wiring shall be done on a distribution system through main and/or branch distribution boards.  The system design as well as the locations of boards shall be as specified by the engineer.

ii) Main distribution board shall be controlled by a circuit breaker or linked switch with fuse.  Each outgoing circuit shall be controlled by a switch with fuse, circuit breaker or only a fuse on the phase or live conductor (as in the case of a TPDB).

iii) The branch distribution board shall be controlled by a linked switch fuse or circuit breaker.  Each outgoing circuit shall be provided with a fuse or miniature circuit breaker (MCB)  of specified rating on the phase or live conductor.

iv) Triple pole distribution boards shall not be used for final circuit distribution, unless specific approval of the engineer is obtained.  In such special cases, the triple pole distribution boards shall be of HRC fuse type or MCB type only.

v) The loads of the circuits shall be divided, as far as possible, evenly between the number of ways of the distribution boards, leaving at least one spare circuit for future extension.

vi) The neutral conductors (incoming and outgoing) shall be connected to a common link (multi-way connector) in the distribution board and be capable of being disconnected individually for testing purposes.

vii) ‘Power’ wiring shall be kept separate and distinct from ‘Lighting’ wiring, from the level of circuits i.e., beyond the branch distribution boards.

viii) Wiring shall be separate for essential loads (i.e. those fed through standby supply) and non-essential loads throughout.

16.2.5.3 Balancing of circuits

i) The balancing of circuits in three wire or polyphase installations shall be arranged before hand to the satisfaction of the engineer.

ii) Circuits on opposite poles of a three wire D.C. system shall be kept apart unless they are enclosed in earthed metal casing, suitably marked to indicate the risk of shock due to the voltage between the conductors contained in them. 

16.2.5.4 Wiring system

i) Unless and otherwise specified in the tender documents, wiring shall be done only by the “Looping system”.  Phase or live conductors shall be looped at the switch boxes and neutral conductors at the point outlets.

ii) Where “joint box system” is specified in the tender documents, all joints in the conductors shall be made by means of approved mechanical connectors in suitable and approved junction boxes.

iii) Lights, fans and call bells shall be wired in the ‘lighting’ circuits.  15A/16A socket outlets and other power outlets shall be wired in the ‘Power’ circuits.  5A/6A socket outlets shall also be wired in the ‘power’ circuit both in residential as well as non-residential buildings. 

iv) The wiring throughout the installation shall be such that there is no break in the neutral wire except in the form of lined switchgear.

16.2.5.5 Run of wiring

i) The type of wiring shall be as specified in tender documents, namely wood batten, casing and capping, or conduit.

ii) Surface wiring shall run, as far as possible, along the walls and ceiling so as to be easily accessible for inspection.

iii) In no case, the open wiring shall be run above the false ceiling without the approval of engineer.

iv).  In all types of wiring, due consideration shall be given for neatness, good appearance and safety.

16.2.5.6 Passing through walls or floors

i) When wiring cables are to pass through a wall, these shall be taken through a protection (steel/PVC) pipe or porcelain tube of suitable size such that they pass through in a straight line without twist or cross in them on either end of such holes.  The ends of metallic pipe shall be neatly bushed with porcelain, PVC or other approved material.

ii) Where a wall pipe passes outside a building so as to be exposed to weather, the outer end shall be bell mouthed and turned downwards and properly bushed on the open end. 

iii) Protection pipe shall be provided for batten wiring passing through floors as specified in clause 3.6 of these specifications.

iv) All floor openings for carrying any wiring shall be suitably sealed after installation. [See also clauses 16.1.8(iii) and 16.1.14(iii)].

16.2.5.7 Joints in wiring

i) No bare conductor in phase and/or neutral or twisted joints in phase, neutral, and/or protective conductors in wiring shall be permitted.

ii) There shall be no joints in the through-runs of cables.  If the length of final circuit or submain is more than the length of a standard coil, thus necessitating a through joint, such joints shall be made by means of approved mechanical connectors in suitable junction boxes.

iii) Termination of multistranded conductors shall be done using suitable crimping type thimbles.

16.2.6 Specifications for ratings of outlets (to be adopted for design)

i) Incandescent lamps in residential and non-residential buildings shall be rated at 60 W and 100 W respectively. 

ii) Ceiling fans shall be rated at 60 W.  Exhaust fan, fluorescent tubes, compact fluorescent tubes, HPMV lamps etc. shall be rated according to their capacity.  Control gear losses shall be also considered as applicable. 

iii) 5A/6A and 15A/16A socket outlet points shall be rated at 100 W and 1000 W respectively, unless the actual values of loads are specified.

16.2.7 Specifications for capacity of circuits

i) “Lighting” circuit shall not have more than a total of 10 points of light, fan and socket outlets, or a total connected load of 800 W, whichever is less. 

ii) “Power” circuit shall be designed with only one outlet per circuit in nonresidential buildings.  The circuit shall be designed based on the load.  Where not specified, the load shall be taken as 1KW per outlet.

iii) “Power” circuit in residential buildings shall be designed for not more than two outlets (15A/16A and/or 5A/6A) per circuit.  The ratings for load calculation purposes shall however be taken as per the type of outlets. [See clause 16.2.10.1(b)] for their wiring].

iv) Load more than 1KW shall be controlled by an isolator or miniature circuit breaker. 

16.2.8 Conformity to 1E act, 1E rules, and standards

i) All electrical works shall be carried out in accordance with the provisions of Indian Electricity Act, 1910 and Indian Electricity Rules, 1956 amended upto date.  ii) In all electrical installation works, relevant safety codes of practice shall be followed. 

16.2.9 General requirements of components

16.2.9.1 Quality of materials - All materials and equipment supplied by the contractor shall be new.  They shall be of such design, size and material as to satisfactorily function under the rated conditions of operation and to withstand the environmental conditions at site.

16.2.9.2 Ratings of components

a) All components in a wiring installation shall be of appropriate ratings of voltage, current, and frequency, as required at the respective sections of the electrical installation in which they are used.

b) All conductors, switches and accessories shall be of such size as to be capable of carrying the maximum current which will normally flow through them, without their respective ratings being exceeded.

16.9.2.3 Conformity to standards

a) All components shall conform to relevant Indian Standard Specification, wherever existing.  Materials with ISI certification mark shall be preferred.  However, for conduits, wiring cables, piano/tumbler switches and socket outlets, ISI marked materials shall only be permitted.

b) The Indian Standards, including amendments or revisions thereof upto the date of tender acceptance, shall be applicable in the respective contracts.

16.2.9.4 Interchangeability - Similar parts of all switches, lamp holders, distribution fuse boards, switchgears, ceiling roses, brackets, pendants, fans and all other fittings of the same type shall be interchangeable in each installation.

16.2.9.5 Categorisation of components

a) Makes of certain items of materials are categorised from time to time by the Department and included in schedule of rates; only those makes of items under the category indicated in tender documents shall be used in the work.

b) For items of materials, for which the department approves makes, only such approved makes shall be permitted in the work.

16.2.9.6 Special risks - Special forms of construction such as flameproof enclosures shall be adopted where there is risk of fire, or explosion and wherever indicated in the tender documents.

16.2.10 SPECIFICATIONS FOR CABLES

16.2.10.1 Wiring Cables

(i) (a) Conductors of wiring cables (other than flexible cables) shall be of aluminium or copper, as specified.

(b) The Government of India in the Gazette notification issued vide order dated 7.5.91 of the Department of Industrial Development under the Ministry of Industry has withdrawn its earlier ban on the use of copper in the manufacture of PVC and VIR wires of domestic type. Consequently, it is left to the discretion of the technically sanctioning authority to use either aluminium or copper wiring in any building or installation.  However, wiring for socket outlets in all residential and non-residential buildings shall be done by using copper conductor cables only. 

(ii) The smaller size of conductor for ‘lighting’ circuits shall have a nominal cross sectional area of not less than 1.5 sq mm.   The minimum size of conductor for ‘power’ wiring shall be 4 sq mm.

(iii) Stranded aluminium conductor shall not be used in wiring cables up to and including 6 sq mm size.

16.2.10.2 Flexible cables

(i) Conductor of flexible cables shall be of copper.  The minimum cross sectional area of conductor for flexible cable shall be 14/0.193 mm.

(ii) Only 3 core flexible cables shall be used for connecting single phase appliances.

(iii) Unless the flexible cables are mechanically protected by armour, or tough rubber, or PVC sheath, these shall not be used in workshops and other places where they are liable to mechanical damage.

(iv) Flexible cable connection to bell push ceiling rose shall be taken through steel conduit/metallic casing and capping.

16.2.11 Specifications for wiring accessories

16.2.11 Control switches for points

(i) Control switches (single pole switches) carrying not more than 16A may be of tumbler or piano type, as specified, and the switch shall be “ON” when the knob is down.

(ii) Control switches of 15A/16A rating may preferably be only of tumbler type.  If, however, piano type switch is used for controlling a sockets outlet, combined switch cum socket shall not be permitted.

(iii) The type and current rating of switch controlling a group of points, or discharge lamps, or a single large load, shall be suitable for the respective loads and as specified in the tender documents

(iv) Power (15A/16A) outlets shall be controlled by single pole tumbler type switches or by ’MCB’s, where specified.  Only MCB’s shall be used for controlling industrial type socket outlets, and power outlets above 1KW.

(v) Control switch shall be placed only in the live conductor of the circuit.  No single pole switch or fuse shall be inserted in the protective (earth) conductor, or earthed neutral conductor of the circuit.

16.2.11.2 Socket outlets

(i) Socket outlets shall be of the same type, namely, piano type or tumbler type, as their control switches.  These shall be rated either for 5A/6A or 15A/16A.  Combined 5A/15A, or 6A/16A six-pin socket outlet may be provided in ‘power’ circuits only where specified.

(ii) (a) In an earthed system of supply, socket outlets and plugs shall only be of 3 pin type; the third pin shall be connected to earth through protective (loop earthing) conductor.  2 pin or 5 pin sockets shall not be permitted to be used, 

(b) Conductors connecting electrical appliances with socket outlets shall be flexible twin    cord with an earthing cord; which shall be secured by connecting between the earth terminal of plug and the metallic body of the electrical appliance.

(iii) Sockets for the power outlets of rating above 1KW shall be of industrial type with associated plug top and controlling MCB.

(iv) Where specified, shutter type (interlocking type) of sockets shall be used.

(v) A socket outlet shall not embody fuse terminal as integral part of it.  But the fuse may be embodied in plug, in which case the plug shall be non-reversible and shall be so arranged and connected that the fuse is connected to phase, or live conductor, or the non earthed conductor of the circuit. 

(vi) Every socket outlet shall be controlled by a switch or MCB, as specified.  The control switch/MCB shall be connected on the ‘live’ side of the line. 

(vii) Outlet boxes for socket outlets (both 15A/16A and 5A/6A) points in residential buildings shall be of size 175 mm x 100 mm.

(viii) 5A/6A and 15A/16A socket outlets shall be installed at the following positions, unless otherwise specified.

  1. Non-residential buildings – 23 cm above floor level.
  2. Kitchen – 23 cm above working platform and away from the likely positions of stove and sink.
  3. Bathroom – No socket outlet is permitted for connecting a portable appliance thereto.  MCB/IC switch may be provided above 2.1 m for fixed appliances, and at least 1 m away from shower.
  4. Rooms in residences – 23 cm above floor level, or any other level in special cases as desired by the engineer.

(ix) Unless and otherwise specified, the control switches for the 5A/6A and 15A/16A socket outlets shall be kept along with the socket outlets:

16.2.11.3 Switch box covers - Phenolic laminated sheets of approved shade shall be used for switch box covers.  These shall be of 3 mm thick synthetic phenolic resin bonded laminated sheet as base material and conforming to grade P-I of IS: 2036-1974.

Note-Specification for switch boxes are covered in the sections on the various types of wiring,

16.2.11.4 Ceiling rose

(i) A ceiling rose shall not be used on a circuit, the voltage of which normally exceeds 250 V.

(ii) Only one flexible cord shall be connected to a ceiling rose.  Specially designed ceiling roses shall be used for multiple pendants.

(iii) A ceiling rose shall not embody fuse terminal as an integral part of it.

16.2.11.5 Lamp holders

(i) Lamp holders may be of batten, angle, and pendant or bracket holder type as required.  The holder shall be made of brass and shall be rigid enough to maintain shape on application of a nominal external pressure.  There should be sufficient threading for fixing the base to the lamp holder part so that they do not open out during attention to the lamp or shade.

(ii) Lamp holders for use on brackets and the like shall have not less than 1.3 cm nipple, and all those for use with flexible pendant shall be provided with cord grips.

(iii) All lamp holders shall be provided with shade carriers.

(iv) Where centre contact Edison Screw lamp holders are used, the outer or screw contact shall be connected to the ‘middle wire’, or the neutral conductor of the circuit.

16.2.12 Specifications for fittings

16.2.12.1 Types – The type of fittings shall be as specified in tender documents.

16.2.12.2 Indoor type fittings

(i) Where conductors are required to be drawn through tube or channel leading to the fitting, the tube or channel must be free from sharp angles or projecting edge, and of such size as will enable them to be the braiding or sheathing.  As far as possible all such tubes or channels should be of sufficient size to permit looping back.

(ii) Pendants in verandahs and similar situations exposed to wind shall be of fixed rod type.

(iii) Vitreous enameled iron shade shall be of size 250 mm x 90 mm (nominal size with a tolerance of 5 mm). Plastic shade should not be generally used in fittings suitable for incandescent lamps.

(iv) Wires used within pre-wired fittings shall be flexible with PVC insulation and 14/0.193 mm (minimum) copper conductors.  The leads shall be terminated on built-in terminal block, ceiling rose or connector, as required.

(v) Fittings using discharge lamps shall be complete with power factor correction capacitors, either integrally or externally.  An earth terminal with suitable marking shall be provided for each fitting for discharge lamps.

(vi) Fittings shall be installed such that the lamp is a height of 2.5 m above floor level, unless otherwise directed by the engineer.

16.2.12.3 Bulk head fittings - Bulk head fittings shall be of cast iron/cast aluminium body, suitably painted white inside and gray outside, complete with heart resistant glass cover, gasket, BC lamp holder for 100 W incandescent lamp, and wire guard. 

16.2.12.4 Outdoor fittings - Fittings for outdoor use shall be of appropriate (weatherproof) design so as to effectively prevent the entry of moisture.  Flexible cord conductors and cord grip lamp holders must not be used where exposed to weather. 

16.2.13 Specifications for switchgear and control gear

(i) All items of switchgear and distribution boards (DBs) shall be metal clad type, except those forming part of cubicle type switchboards, in which case the board design shall be such as not to permit direct contact.

(ii) The types, ratings and/or categories of switchgear and protective gear shall be as specified in the tender Schedule of work.

(iii) RCDs (ELCBs) where specified, shall conform to the requirements of current rating, fault rating, single phase or three phase configuration and sensitivity laid down in the tender documents.

(iv) While each outgoing way of distribution board (DB) shall be of fuse, or miniature circuit breaker (MCB) as specified, and of suitable rating on the phase conductor, the corresponding earthed neutral conductor shall be connected to a common neutral terminal block and shall be capable of being disconnected individually for testing purposes.

(v) Independent earth terminal block

Every distribution board (single phase as well as 3 phase) shall have an earth terminal block identical to, but independent from neutral terminal block, to enable termination of protective (loop earthing) conductors (incoming as well as outgoing) individually by screwed connection and without twisting.

(vi) Earthing terminal (1 for single phase and 2 for 3 phase) shall be provided on the metal cladding of switches and DBs for body earthing.  These shall be suitably marked.

(vii) Knock out holes, with or without end plates as per standard design of manufacturers, shall be provided in the metal cladding of switches and DBs for termination of conduits/cables.

(viii) Each distribution board shall be provided with a circuit list giving details of each circuit, which it controls, and the current rating of the circuit, and the size of the fuse element.

16.2.14 Specifications for rewireable type iron clad distribution boards (ICDB)

(i) ICDB’s may be used only in single phase AC applications at the final distribution board level for a maximum continuous loading of 15A/way.

(ii) ICDB’s shall be of 2, 4, 6 or 8 ways as specified.

(iii) ICDB’s shall be of surface mounting type only.

(iv) The busbar used shall be solid electrolytic copper of appropriate section.

(v) Consumer unit

Where specified, the controlling switchgear may form part of the ICDB as a ‘consumer unit’.  The number and rating of outgoing as per (ii) above and the incomer rating shall be specified in such units. Busbars in such units shall also be correspondingly shorter.  The inter connections shall be done between the incomer and outgoing as part of the DB in the works.

16.2.15 Specifications for HRC type distribution boards

(i) HRC type distribution board shall be used in selected locations [see also clause 2.5.2(iv)]. The rating shall be 16/32/63/100A per way and the number of ways shall be 4 or 8 as a TPNDB as specified.

(ii) These shall be dust and vermin proof conforming to IP42, and fabricated out of sheet steel with stove enameled paint finish,

(iii) The DBs shall be of surface mounting type, and shall be provided with electrolytic copper busbars of suitable size.

(iv) DB s shall have phase barriers and earth terminals.

(v) DBs shall have removable type end covers with knock-outs at the bottom and top, and shall have hinged covers with locking arrangements.

16.2.16 Specifications for MCB type distribution boards (MCBDB)

(i) MCBDB’s may be of single phase, 3 phase (horizontal type) suitable for feeding single phase loads, or 3 phase (vertical type) suitable for feeding single phase as well as 3 phase 3 phase loads, as specified.  These shall be complete with accessories, but without MCBs, which shall be specified as a separate item in the tender documents.

(ii) The current ratings and the number of ways shall be as specified.  Blanking plates shall be provided to close unused ways.  These shall be indicated as a separate item in the Schedule of work. 

(iii) DB with integral incomer

Where it is proposed to install the controlling MCB/MCB type isolator/both, the total number of outgoing MCBs will be reduced by one or two numbers corresponding to SP or SP&N at the incoming, since the total number of ways are fixed in MCBDBs.  Busbars in such units shall also be correspondingly shorter.  The inter connections shall be done between the incomer and outgoing as part of the DB in the works.

(iv) MCBDB’s shall be of surface/flush mounting pattern according to the requirement of their location, and shall be suitable to accommodate MCB’s and MCB type isolators and RCD (ELCB) at incoming in single pole or multiple configuration, as required.

(v) MCBDB’s shall be dust and vermin proof conforming to IP 42, and shall be fabricated out of CRCA sheet steel, 1.6 mm thick, with stove enameled paint finish. 

(vi) MCBDB’s shall have removable type end plates with knockouts at the bottom and top, and shall have hinged covers with locking arrangement.

(vii) Only the knobs of the MCBs shall protrude out of the front covers through openings neatly machine made for the purpose.

(viii) The busbars used shall be solid electrolytic copper of appropriate sections.

(ix) DIN bar(s) shall be provided for mounting the MCB’s.

16.2.17 Specifications for pre-wired MCB distribution boards

(i) Previewed MCBDBs shall be provided only where specified.

(ii) The complete board shall be factory fabricated and shall be duly pre-wired in the works, ready for installation at site.

(iii) The board shall be of wall mounted, cubical type construction, fabricated out of 1.6 mm thick sheet steel, with stove enameled paint finish.

(iv)The board shall also be provided with a loose wire box as a compartment for the complete width and, depth of the board, and of minimum height of 125 mm in case of TPN DB’s, and 100 mm in case of SPN DB’s.

(v) The board shall be provided with a hinged cover of 1.6 mm thick sheet steel in the front.  Only the knobs of the MCBs shall protrude out of the front covers through openings neatly machine made for the purpose. 

(vi) Knock out holes at the bottom, and detachable plate with knock out holes at the top of the board shall be provided.

(vii) The board shall be complete with the following accessories:-

  1. 200 A copper busbar(s).
  2. Neutral link.
  3. Common earth bar.
  4. DIN bar for mounting MCBs.
  5. Elemex type terminal connectors suitable for incoming and outgoing cables.
  6. A set of indication lamps with HRC cartridge fuses for each phase of the incoming supply.
  7. Earthing stud(s).

Note – MCB’s and blanking plates shall be specified as separate items, as  required.

(viii) The board shall be fully prewired with single core PVC insulated copper conductors/insulated solid copper links, and terminated on to extended type terminal connectors, suitable for connections to the sizes of the respective conductors.

(ix) All incoming and outgoing wiring to the prewired MCBDB’s shall be terminated only in the Elemex type extended terminal connectors to be provided within the DB.  The terminal connectors shall, therefore, be so provided as to facilitate easy cable connections and subsequent maintenance.

(x) A common copper earth bar shall be provided within the loose wire box.  The common neutral bar as well as the terminal connectors shall, however, be provided within the main compartment just below the loose wire box. 

16.2.18 Specifications for miniature circuit breakers (MCB’S)

(i) ‘L’ series MCB’s shall be used only for normal ‘lighting’ circuits.

(ii) ‘G’ series MCB’s shall be invariably used for motor loads, halogen lamp fittings, sodium/mercury discharge lamps and all ‘power’ circuits.

(iii) Ratings (A as well as KA), number of poles, type as MCB or isolator, etc. shall be as specified in the tender documents.

16.2.19 Specifications for switchboards

(i) All items of switch gear and distribution boards (DB’s) shall be installed on switchboards. [See (ii) below)]

  1. Where specified by the engineer, only MCBDB’s may be permitted to be installed directly recessed in wall without switchboards.  In such cases, the metal cladding of the DB shall be suitable for recess mounting.
  2. Switchboards be one of the following types, as specified.
  1. Hinged type.
  2. Fixed type.
  3. Enclosed cubicle type.

16.2.20 Switchboards locations

16.2.20.1 General aspects

(i) Switchboards shall be located as per drawings.

(ii) As far as practicable, the boards should be accessible from common areas like corridors, lobby areas, etc.

(iii) Switchboards shall be located only in dry situations and in well ventilated spaces.  They shall not be placed in the vicinity of storage batteries and exposed to chemical fumes.

(iv) Switchboards shall not be erected above gas stoves or sinks or within 2.5 m of any washing unit in the washing rooms of laundries, or in the bathrooms, toilets or kitchens.

16.2.20.2 Main switchboards

(i) Main switchboards shall be situated as near as practicable to the termination of service line, and shall be easily accessible without the use of any external aid, to quickly disconnect the supply in case of emergencies.

(ii) Main switchboards shall be installed in rooms, or cupboards, or suitable enclosed space having provisions for locking arrangement so as to safeguard against operation by unauthorised personnel.

16.2.20.3 Distribution switchboards

(i) The distribution boards shall be located as near as possible to the centre of the load they are intended to control. These boards shall be fixed on suitable stanchion or wall, and shall be accessible for attention to fuses / MCBs.

(ii) Where two or more distribution boards feeding low pressure circuits are fed from a supply at medium voltage, these distribution boards shall be :-

  1. Fixed not less than 2 m apart; or
  2. Arranged so that two cannot be opened at a time, namely, they are interlocked, and the metal case is marked “Danger-400V”; or
  3. Installed in a room or enclosure accessible to only authorised persons.

16.2.21 Switchboard construction

16.2.21.1 Hinged type switchboards

(i) Hinged type boards shall be suitable for mounting of metal clad switchgear consisting of not more than one switch gear and one ICDB, 4 way or 6 way, 15A per way.

(ii) The board shall consist of a box made of sheet metal not less than 3 mm thick, and shall be provided with a hinged cover to enable the board to be swung open for the examination of their wiring at the back.  The joints shall be substantially welded. 

(iii) Alternatively, the board may be made of suitable size along iron of minimum size 35 mm x 35 mm x 6 mm, or channel iron of minimum size 35 mm x 25 mm x 6 mm frame work, suitably mounted on front with a 3 mm thick MS plate, and on back with1.5 mm MS sheet.  In case of wood batten system of wiring, the top and bottom members may be replaced by 2.5 cm teak wood battens.  The front sheet shall be provided with locking arrangement and suitable hinges to enable the board to swing open for examination of the wiring.  The joints shall be substantially welded.

(iv) There shall be a clear distance of 3 cm between the front and back sheets.  More space shall be allowed wherever necessary.

(v)The board shall be provided with an earthing stud.  The earth stud should be commensurate with the size of the earth lead.

(vi) Suitable hole shall be drilled to take the wiring as well as for fixing the mountings.  No hole shall be drilled closer than 1 cm from any edge of the board.

16.2.21.2 Fixed type switchboards

(i) The design shall be wall/floor mounted, or wall cum floor mounted, as specified.

(ii) The board shall be fabricated of channel iron, angle iron and/or flat iron, as required.  Shop drawings showing the detailed dimensions and design, including the disposition of the various mountings, (which shall as far as practicable be symmetrical) shall be submitted by the contractor and got approved from the engineer before fabrication.

(iii) Necessary hold-fast or supports shall be welded to the frame work.

(iv) An earth bar shall be provided for termination of protective (earth) conductors (incoming as well as outgoing).  This shall be complete with necessary studs (one for each conductor) and washers.

(v) Measurement - The front area in sq.m shall measure fixed type switchboards. For boards, which are supported on the floor, the area shall be measured after taking into consideration the vertical legs also.

16.2.21.3 Cubical type switchboards- Cubical type switchboards shall conform to Section 4 of “General Specifications for Electrical Works (Part-IV-Substation), 1982”.

16.2.21.4 Common requirements for all types of switchboards

(i) Switchboards, if unavoidably fixed in places likely to be exposed to weather, to drip, or to dampness, their outer casing shall be weather proof, and shall be provided with glands or bushings or adopted to receive screwed conduits according to the manner in which the cables are run.  PVC and double flanged bushes shall be fitted in the holes of the switches for entry and exit of wires.

(ii) When it is unavoidable to install in a situation where inflammable, or explosive dust, vapours or gas is likely to be present, the switchboards shall be totally enclosed, or made flameproof as may be necessitated by the particular circumstances.

(iii) The various live parts, unless they are effectively screened by substantial barriers of non hygroscopic, non-inflammable, insulating material, shall be so spaced that an arc cannot be maintained between such parts and with earth.

(iv) In every case in which switches and fuses are fitted on the same pole, these fuses shall be so arranged that the fuses are not alive when their respective switches are in the ‘off’ position.

(v) No fuses, other than fuses in instrument circuit, shall be fixed on the back of, or behind a switchboards panel, or frame.

(vi) Equipment, which are on the front of a switchboards shall be so arranged that inadvertent personal contact with live parts (direct contact) is likely during the manipulation of switchgears, changing of fuses, or like operations.

(vii) The arrangement of the gear shall be such that they shall be readily accessible, and their connections to all instruments and apparatus shall be easily traceable.

(viii) Interconnections of the various mountings on the boards shall be done using PVC insulated conductors, or solid strips with PVC taping/sleeving, of appropriate sizes.  Terminations shall be made such that local heating is avoided.

(ix) No holes, other than the holes by means of which the panel is fixed, shall be drilled closer than 1 cm from any edge of the panel.

(x) All the metalwork of switchboards shall be painted prior to erection with one coat of anti-rust primer.  After erection, they shall be painted with two coats of appropriate enamel, or aluminium paint as required, on all sides wherever accessible.

(xi) All switchboards shall be provided with “Danger Notice Plate” conforming to relevant Indian Standards.  If required in the tender specifications, a pilot lamp shall be fixed and connected through an independent single pole switch and fuse to the busbars of the board.

16.2.22 Specifications for switchboard installation

(i) Unless and otherwise specified in the tender documents, a switchboards shall not be installed so that its bottom is within 1.25 m above the floor, unless the front of the switchboards is completely enclosed by a door, or the switchboards is located in a position to which only authorised persons have access.

(ii) The switchboards inside a residence shall be installed such that the operating knob/handle of the incomer is at a height of about 2 m for ease of operation at times of emergency.

(iii) There shall be a clear space of 1m in front of the switchboards. The space behind the switchboards shall be either less than 20 cm or more than 75 cm.  If there are any attachments or bars connections at the back of the switchboards, Rule 51© of the Indian Electricity Rules shall apply.

(iv) Hinged type boards shall be securely fixed on wall by means of rag bolts.  Fixed type boards shall be installed by suitably grouting the frame work on the wall and/or floor as required.  Cubicle type boards shall be installed by suitable foundation bolts grouted in the floor, or alternatively, over masonry cable trenches on necessary channel sections, duly grouted as required.

(v) Cubical type switchboards shall be recessed in the wall if so specified in the tender documents.  The front shall then be fitted with hinged panel with locking arrangement, the outer surface of door being flush with the wall.  Ample room shall be provided for the wiring/cable connections at the side and at the front between the switchgear mountings and the door.

(vi) (a) The connections between the switchgear mounting and the outgoing cable upto the wall shall be enclosed in a protection pipe.

(b) Where it is required to terminate a number of conduits on a board, it may be convenient to provide a suitable MS adopter box for the purpose.  Such boxes shall be provided with the prior approval of the engineer and this will be paid for separately.

 (vii) All wires to the boards shall be bushed at the entries to avoid damage to insulation.

(viii) No apparatus shall project beyond any edge of the panel.  No fuse body shall be mounted within 2.5 cm of any edge of the panel.

(ix) Busbars and interconnecting strips in fabricated boards shall be PVC taped or sleeved in Red, Yellow, and Blue for phases, and Black for neutral.  The interconnecting cables shall also follow this colour coding.

(x) All round holes in the boards and in the mountings shall be plugged suitably to avoid entry of insects.

16.2.23. Wiring of switchboards and distribution boards

(i) All connections between pieces of apparatus, or between apparatus and terminals on boards shall be neatly arranged in a definite sequence, following the arrangement of the apparatus mounted thereon, avoiding unnecessary crossings.

(ii) Cables shall be connected to terminals either by crimped or soldered lugs, unless the terminals are of such a form that they can be securely clamped without cutting away of cable strands.

(iii) All bare conductors shall be rigidly fixed in such a manner that a clearance of at least 2.5 cm is maintained between conductors of opposite polarity or phase, and between the conductors and any material other than insulating material.

(iv) In a hinged type board, the incoming and outgoing cables shall be neatly bunched and shall be fixed in such a way that the door shall be capable of swinging through an angle of not less than 90 degrees.

16.2.24. Marking of apparatus

(i) Marking of earthed neutral conductor  - On the main switchgear, where the conductors include an earthed conductor of a two-wire system, or an earthed neutral conductor of a multi-wire system, or a conductor which is to be connected thereto, an indication of a permanent nature shall be provided to identify the earthed neutral conductor.  In this connection Rule 32(1) of Indian Electricity Rules 1956 shall be referred to.  The neutral conductor shall be black in colour.

(ii) Main earthing terminal - The main earthing terminal in the main switchboard shall be permanently marked as “SAFETY EARTH – DO NOT REMOVE”.

(iii) Where a board has more than one switchgear, each such switchgear shall be marked to indicate which section of the installation it controls.  The main switchgear shall be marked as such. Where there is more than one main switchboard in the building, each such switchboard shall be marked to indicate which section of the installation and building it controls.

(iv) All distribution boards shall be marked ‘L’ for lighting or ‘P’ for power and ‘E’ for essential as the case may be.

(v) When a board is connected to a voltage higher than 250V, all the terminals or leads of the apparatus mounted on it shall be marked in the following colour to indicate the different poles or phases to which the apparatus or its different terminals may have been connected. 

A.C.

D.C.

Three phases – Red,

Blue & Yellow

Neutral – Black

Three wire system

2 outer wires – Red & Blue

Neutral - Black

 (vi) Where a four wire, three phase wiring is done, the neutral shall preferably be in one colour, and the other three wires in another colour.

(vii) All marking required under this rule should be clear and permanent.

16.2.25 Attachment of fittings and accessories

16.2.25.1 Conduit wiring system

(i) All accessories like switches socket outlets call bell pushes and regulators shall be fixed in flush pattern inside the switch/regulator boxes.  Accessories like ceiling roses, bracket, batten holders, stiff pendants, etc, and shall be fixed on metal outlet boxes.  The fan regulators may also be fixed on metal outlet boxes, if so directed by the engineer.

(ii) Aluminium alloy or cadmium plated iron screws shall be used to fix the accessories to their bases.

(iii) The switch box/regulator box shall normally be mounted with their bottom 1.25 m from floor level, unless otherwise directed by the engineer.

16.2.25.2 Wood batten-wiring system - The specifications given hereunder are subject to clause 3.0 of these specifications.

(i) Accessories like ceiling rose, brackets, battens, stiff pendants, etc, shall be mounted to ceiling or wall on substantial blocks of teak wood or approved hard wood double board construction, twice varnished both inside and outside including backside after all fixing holes are made in them.  Block shall not be less than 4 cm deep.

(ii) Accessories like switches, socket outlets, call bell pushes, etc. shall be flush mounted inside substantial box of teak wood or approved hard wood double board construction, twice varnished both inside and outside including back side after all fixing holes are made in them, and attached to the wall.  Blocks shall not be less than 4 cm deep.  The cover for the box or block shall be of phenolic laminated sheet.

(iii) Groups of accessories and regulators shall be mounted on well seasoned and properly secured double teak wood or approved hard wood boards of suitable size to accommodate the number of fittings.  The board shall be well varnished with pure shellac on all sides both inside and outside, irrespective of being painted to match the surroundings.  The board shall be divided into two sections, one for the switches, which shall be flush mounted, and the other for regulators fixed on the board with suitable flat washers and round head iron screws (or any other type of screws as required).  The cover for section accommodating switches and socket outlets shall be of phenolic laminated sheet.

(iv) Wherever possible, the control boxes shall be recessed and in such cases metal boxes conforming to 4.2.3 shall be used. The metal boxes shall be suitably earthed.

(v) Alternatively, switches may be surface mounted on teak wood or where the fan clamp mentioned under sub-clause (v) above cannot be used, or wherever specified, recessed type fan clamp inside a metallic box, as shown in fig.2 shall be used.

(vi) Canopies on top of suspension rod shall effectively hide the suspension

(vii) The leading in wire shall be of nominal cross sectional area not less than 21.5 sq. mm and shall be protected from abrasion.

(viii) Unless otherwise specified, all ceiling fans shall be hung 2.75 m above the floor.

(ix) In the case of measurement of extra down rod for ceiling fan including wiring, the same shall be measured in units of 10cm.  Any length less than 5cm shall be ignored.

(x) The wiring of extra down rod shall be paid as supplying and drawing cable in existing conduit.

16.2.27.2 Exhaust fans

(i) Exhaust fans shall conform to relevant Indian Standards.

(ii) Exhaust fans shall be erected at the places indicated by the engineer.  For fixing an exhaust fan, a circular hole shall be provided in the wall to suit the size of the frame, which shall be fixed by means of rag bolts, embedded in the wall.  The holes shall be neatly plastered to the original finish of the wall.  The wall exhaust fan shall be connected to the exhaust fan point, which shall be wired as near to the hole as possible, by means of a flexible cord, care being taken to see that the blades rotate in the proper direction.

(iii) Exhaust fans for installation in corrosive atmosphere, shall be painted with special PVC paint or chlorinated rubber paint.

(iv) Installation of exhaust fans in kitchen, dark rooms and such other special locations need careful consideration; any special provisions needed shall be specified.

16.2.27.3 Regulators - Protective conductor shall connect the metallic body of regulators of ceiling fans/exhaust fans to earth.

16.2.28 Workmanship

(i) Good workmanship is an essential requirement to be complied with.  The entire work of manufacture/fabrication, assembly and installation shall conform to sound engineering practice.

(ii) The work shall be carried out under the direct supervision of a first class licensed foreman, or of a person holding a certificate of competency issued by the State Govt. for the type of work involved, employed by the contractor, who shall rectify then and there the defects pointed out by the engineer during the progress of work.

16.2.29 Commissioning on completion - Before the workman leaves the work finally, he must make sure that the installation is in commission, after due testing.

16.2.30 Completion plan and completion certificate

(i) For all works costing more than Rs. 20,000, completion certificate after completion of work shall be submitted to the engineer.

(ii) Completion plan drawn to a suitable scale in tracing cloth with ink indicating the following, along with three blue print copies of the same shall also be submitted.

  1. General layout of the building.
  2. Locations of main switchboards and distribution boards, indicating the circuit numbers controlled by them.
  3. Position of all points and their controls.
  4. Types of fittings, viz. fluorescent, pendants, brackets, bulkhead, fans and exhaust fans etc.
  5. Name of work, job number, accepted tender reference, actual date of completion, names of Division/Sub-Division, and name of firm who executed the work with their signature.

(iv) In the case of works costing less than Rs.20, 000, the completion plan shall be prepared by the department and signed by the contractor before final payment is made.

16.2.31 Addition to an Installation - An addition, temporary or permanent, shall not be made to the authorised load of an existing installation until it has been definitely ascertained that the current carrying capacity and the condition of the existing accessories, conductors, switches, etc. affected, including those of the supply authorities, are adequate for the increased load.

16.2.32 Connection to ancillary buildings

(i) Unless otherwise specified, electrical connections to ancillary buildings such as out-houses, garages, etc adjacent to the main building at a distance not greater than 3 m, and when nor road intervenes, shall be taken in an earthen GI pipe of suitable size in the exposed portion at a height of not less than 2.5 m.  This applies to both runs of mains or sub-mains or circuit wiring between the buildings.

(ii) When the distance between the buildings exceed 3 m, ir a road way intervenes, separate mains, or sub-mains shall be run from the main building to ancillary building and the portion of the same exposed to weather shall be carried in weather proof cable on GI bearer wire at a height not less than 4 m above the ground level.  Alternatively, PVC wires in GI pipe, or underground cable may be used below ground level.

16.2.33 Drawings

(i) The work shall be carried out in accordance with the drawings enclosed with the tender documents and also in accordance with modification thereto from time to time as approved by the engineer.

(ii) All wiring diagrams shall be deemed to be ‘Drawings’ within the meaning of the term as used in the conditions of contract. They shall indicate the main switchboards, the distribution boards (with circuit numbers controlled by them), the runs of various mains and sub-mains and the position of all points with their controls.

(iii) All circuits shall be indicated and numbered in the wiring diagram and all points shall be given the same number as the circuit to which they are electrically connected.

16.2.34 Maintenance - Annexure 16-A.1 indicates certain requirements to be met by the engineers of the department, in addition to those to be met by the contractors.  This is applicable both for construction and maintenance works.  The periodicity of important maintenance activities is also indicated in Annexure-16-A.1.

16.3 SPECIFICATIONS WITH PVC INSULATED AND PVC SHEATHED WIRING SYSTEM

16.3.0 Scope - This section covers the detailed requirements for the wiring works on wood batten, using PVC sheathed conductors.

16.3.1 Application

(i) This system of wiring is normally not to be used in view of the ban on use of timber in Govt. works sanctioned after 1.4.93.  However in exceptional cases, this system of wiring may be resorted to with the prior approval of the competent authority.

(ii) This system of wiring is suitable for low pressure installation, and shall not be used in places exposed to sun and rain, nor in damp places, but it can be installed in the above places provided they are sheathed in special approved protective covering, and well protected to withstand dampness.

16.3.2 Materials

16.3.2.1 Wood batten - Wood batten shall be of well-seasoned teakwood, or any approved hard wood not less than 10 mm thick width.  The width shall be such as to suit the total width of cables to be laid on the battens.

16.3.2.2 Link clips - Only aluminium alloy clips/joint clips shall be used.  The thickness shall be 0.32mm (30SWG) for lengths of 25 mm to 40 mm, and 0.40 mm (28SWG) for lengths of 50 mm to 80 mm.  The width shall not be less than 8 mm in all these cases.

16.3.2.3 Hardware items

(i) Galvanised/cadmium plated, chamfered and flat head wood screws shall be used for fixing the batten.  Iron pins used for fixing link clips should be at least 6 mm long and be galvanised / anodized.

(ii) Clamps to be used for clipping battens to the rolled steel joist shall be of 1.6 mm thickness and 10 mm width mild steel.

16.3.3 Installation

16.3.3.1 Attachment to walls and ceiling

(i) Prior to erection, the wood batten shall be painted with one coat of varnish, or approved paint of colour to match with the surroundings.

(ii) The battens shall be secured to the walls and ceiling by flat head wood screws to rawl plug, or phil plug at an interval not exceeding 75 cm.  The screws shall be counter sunk within the battens.

(iii) Where the battens are to be fixed to rolled steel sections, MS clamps, 1.2 mm thick, and 19 mm wide, shall be used for clipping the battens to the same as inconspicuously as possible.

(iv) Where it is required to attach the battens to the false ceiling, the same shall be done in a manner that will be suitable for the material of the false ceiling and its support frame.

(v) The wiring shall not in any circumstance be bent so as to form an abrupt right angle, but must be rounded off at the corners to a radius not less than six times the overall diameter of the cable.

16.3.3.2 Fixing of wiring cables

(i) The link clips shall be fixed on varnished wood battens with iron pins, and shall be spaced at intervals of 15 cm, both in the case of horizontal and vertical runs.

(ii) The link clips/joint clips shall be so arranged that one single clip shall not hold more than two twin core, or three single core PVC insulated and PVC sheathed cables up to 1.5 sq.mm, above which a single clip shall hold a single twin core or two single core cable. 

(iii) Where the batten width demands provision of more than one clip at each section, the clips should not be fixed side by side, but be somewhat staggered so as to avoid any gap between cables, and at the same time, giving a neat finish to the wiring work.

(iv) The cables shall be neatly fixed taut without kinks or undulations.

16.3.3.3 Protection of wiring from mechanical damage - In cases where there are chances of any damage to the wiring, such wiring shall be covered with a sheet metal protective covering (not less than 1.6 mm thick), the base of the covering being flush with the plaster or brick work as the case may be, or the wiring shall be drawn through a heavy guage metal conduit pipe by complying with all the requirements of conduit wiring system. 

Such protective covering shall in all cases be fitted on all down drops within 1.5 meters from the floor, or from floor level upto the switch board, whichever is less.

16.3.3.4 Passing through floors and wall - The cables passing though walls and/or floor shall be taken through PVC/steel conduit at such crossings.  In no case, the cables shall be directly buried within the masonry, or roof structure.

16.3.3.5 Stripping of outer covering of cables - While cutting and stripping the outer covering of the cable, care shall be taken to see that the sharp edge of the cutting instrument does not touch the inner insulation of the conductors. The protective outer covering of the cables shall be stripped off near the connecting terminal, and this protective covering shall be maintained upto the close proximity of connecting terminals as far as practicable.

16.3.3.6 Painting - The wiring shall, after erection, be neatly painted in compliance with clauses under Chapter 10 on painting. 

16.4 SPECIFICATIONS FOR METALLIC CONDUIT WIRING SYSTEM

16.4.0 Scope - This section covers the detailed requirements for wiring work in metallic conduits.  This section covers both surface and recessed types of works.

16.4.1 Application

(i) Recessed conduit is suitable generally for all applications.  Surface conduit work may be adopted in places like workshops, plant rooms, pump rooms, wiring above false ceiling/below false flooring, and at locations where recessed work may not be possible to be done.  The type of work, viz. surface or recessed, shall be as specified in the respective works.

(ii) Flexible conduits may only be permitted for interconnections between switchgear, DB’s and conduit terminations in wall.

16.4.2 Materials

16.4.2.1 Conduits

(i) All rigid conduit pipes shall be of steel and be ISI marked.  The wall thickness shall be not less than 1.6 mm (16 SWG) for conduit up to 32 mm dia and not less than 2 mm (14 SWG) for conduits above 32 mm dia.  These shall be solid drawn or reamed by welding, and finished with galvanised or stove enameled surface.

(ii) The maximum number of PVC insulated cables conforming to IS: 694-1990 that can be drawn in one conduit is given size wise in Table I, and the number of cables per conduit shall not be exceeded.  Conduit sizes shall be selected accordingly in each run.

(iii) No steel conduit less than 20 mm in diameter shall be used.

16.4.2.2. Conduit accessories

(i) The conduit wiring system shall be complete in all respects, including their accessories.

(ii) All conduit accessories shall be of threaded type, and under no circumstances pin grip or clamp grip type accessories shall be used.

(iii) Bends, couplers, etc. shall be solid type in recessed type of works and may be solid or inspection type as required, in surface type of works.

(iv) (a) Saddles for surface conduit work on wall shall not be less than 0.55 mm (24 gauge) for conduits up to 25 mm dia and not less than 0.9 mm (20 gauge) for larger diameter.  The corresponding widths shall

(b) The minimum width and the thickness of girder clips used for fixing conduits to steel joists, and clamps shall be as per Table II.

16.4.2.3 Outlets

(i) The switch box or regulator box shall be made of metal on all sides, except on the front. In the case of cast boxes, the wall thickness shall be at least 3 mm and in case of welded mild steel sheet boxes, the wall thickness shall not be less than 1.2 mm (18 gauge) for boxes up to a size of 20 cm x 30 cm, and above this size 1.6 mm (16 gauge) thick MS boxes shall be used.  The metallic boxes shall be duly painted with anticorrosive paint before erection as per specifications.

(ii) (a) Outlet boxes shall be of one of the size, covered in the Schedule of Rates (Elect.),

(b) Where a large number of control switches and/or fan regulators are required to be installed at one place, these shall be installed in more than one outlet box adjacent to each other for ease of maintenance.

(iii) An earth terminal with stud and 2 metal washers shall be provided in each MS box for termination of protective conductors and for connection to socket outlet/metallic body of fan regulator etc.

(iv) A metal strip shall be welded/screwed, to the metal box as support if tumbler type of control switches, sockets and / or fan regulators are to be fixed there in. 

(v) Clear depth of the box shall not be less than 60 mm, and this shall be increased suitably to accommodate mounting of fan regulators in flush pattern.

(vi) The fan regulators can also be mounted on the switch box covers, if so stipulated in the tender specifications, or if so directed by the engineer.

(vii) Except where otherwise stated, 3 mm thick phenolic laminated sheets shall be fixed on the front with brass screws, or aluminium alloy / cadmium plated iron screws as approved by the engineer.

16.4.3 Installation

16.4.3.1 Common aspects for recessed and surface conduit works.

(a) The conduit work of each circuit or section shall be completed before the cables are drawn in.

(b) Conduit pipes shall be joined by means of screwed couplers and screwed accessories only.  Threads on conduit pipes in all cases shall be between 13 mm to 19 mm long, sufficient to accommodate pipes to full threaded portion of couplers or accessories. 

(c) Cut ends of conduit pipes shall have neither sharp edges, nor any burrs left to avoid damage to the insulation of the conductors while pulling them through such pipes.

(d) The engineer, with a view to ensuring that the above provision has been carried out, may require that the separate lengths of conduit etc., after they have been prepared, shall be submitted for inspection before being fixed.

(e) No bare threaded portion of conduit pipe shall be allowed, unless such bare threaded portion is treated with anticorrosive preservative or covered with approved plastic compound.

(1). Bends in conduit

(a) All necessary bends in the system, including diversion, shall be done either by neatly bending the pipes without cracking with a bending radius of not less than 7.5 cm, or alternatively by inserting suitable solid or inspection type normal bends, elbows or similar fittings, or by fixing cast iron inspection boxes, whichever is most suitable.

(b) No length of conduit shall have more than the equivalent of four-quarter bends from outlet to outlet.

(c) Conduit fittings shall be avoided as far as possible on conduit system exposed to weather.  Where necessary, solid type fittings shall be used.

(2). Outlets

(a) All outlets such as switches, wall sockets etc. may be either flush mounting type, or of surface mounting type, as specified in the additional specifications.

(b) All switches (except piano type switches), socket outlets and fan regulators shall be fixed on metal strips which shall be screwed/welded to the box.  Piano type switches and accessories shall be fixed on the phenolic laminated sheet covers in flush pattern.

(3). Painting after erection - After installation, all accessible surfaces of conduit pipes, fittings, switch and regulator boxes etc. shall be painted in compliance with the clauses under section on “Painting”.

16.4.3.2 Additional requirements for surface conduit work.

(1).  Painting before erection - The outer surface of conduit including all bends, unions, tees, junction boxes, etc. forming part of the conduit system, shall be adequately protected against rust when such system is exposed to weather, by being painted with 2 coats of red oxide paint applied before they are fixed.

(2). Fixing conduit on surface

(a) Conduit pipes shall be fixed by saddles, secured to suitable approved plugs with screws in an approved manner at an interval of not more than one meter, but on either side of the couplers or bends or similar fittings, saddles shall be fixed at a distance of 30 cm from the centre of such fittings. 

(a) Where conduit pipes are to be laid along the trusses, steel joists etc. the same shall be secured by means of saddles or girder clips or clamps as required by the engineer.

(b) In long distance straight run of conduit, inspection type couplers at reasonable intervals shall be provided, or running threads with couplers and jam nuts shall be provided.

(3). Fixing outlet boxes - Only a portion of the switch box shall be sunk in the wall, the other portion being projected out for suitable entry of conduit pipes into the box.

16.4.3.3 Additional requirements for recessed conduit work

(1). Making chase

(a) The chase in the wall shall be neatly made, and of ample dimensions to permit the conduit to be fixed in the manner desired.

(b) In the case of buildings under construction, the conduits shall be buried in the wall before plastering, and shall be finished neatly after erection of conduit.

(c) In case of exposed brick/rubble masonry work, special care shall be taken to fix the conduit and accessories in position along with the building work.

(2). Fixing conduits in chase

(a) The conduit pipe shall be fixed by means of staples, J-hooks, or by means of saddles, not more than 60 cm apart, or by any other approved means of fixing.

(b) All threaded joints of conduit pipes shall be treated with some approved preservative compound to secure protection against rust.

(3). Fixing conduits in RCC work

(a) The conduit pipes shall be laid in position and fixed to the steel reinforcement bars by steel binding wires before the concreting is done.  The conduit pipes shall be fixed firmly to the steel reinforcement bars to avoid their dislocation during pouring of cement concrete and subsequent tamping of the same. 

(b) Fixing of standard bends or elbows shall be avoided as far as practicable, and all curves shall be maintained by bending the conduit pipe itself with a long radius which will permit easy drawing in of conductors.

(c) Location of inspection/junction boxes in RCC work should be identified by suitable means to avoid unnecessary chipping of the RCC slab subsequently to locate these boxes.

(4). Fixing inspection boxes

(a) Suitable inspection boxes to the minimum requirement shall be provided to permit inspection, and to facilitate replacement of wires, if necessary.

(b) These shall be mounted flush with the wall or ceiling concrete.  Minimum 65 mm depth junction boxes shall be used in roof slabs and the depth of the boxes in other places shall be as per IS: 2667-1977.

(c) Suitable ventilating holes shall be provided in the inspection box covers.

(5). Fixing switch boxes and accessories - Switch boxes shall be mounted flush with the wall.  All outlets such as switches, socket outlets, etc. shall be flush mounting type, unless otherwise specified in the Additional Specifications.

(6).  Fish wire - To facilitate subsequent drawing of wires in the conduit, GI fish wire of 1.6 mm/1.2 mm (16/18 SWG) shall be provided along with the laying of the recessed conduit.

(vii) Bunching of cables

(a) Cables carrying direct current may, if desired, be bunched whatever their polarity, but cables carrying alternating current, if installed in metal conduit shall always be bunched so that the outgoing and return cables are drawn into the same conduit.

(b) Where the distribution is for single-phase loads only, conductors for these phases shall be drawn in one conduit.

(c) In case of three phase loads, separate conduits shall be run from the distribution boards to the load points or outlets as the case may be.

16.4.3.4 Earthing requirements

(1). The entire system of metallic conduit work, including the outlet boxes and other metallic accessories, shall be mechanically and electrically continuous by proper screwed joints, or by double checknuts at terminations.  The conduit shall be continuous when passing through walls or floors.

(2). Protective (loop earthing) conductor(s) shall be laid along the runs of the conduit between the metallic switch boxes and the distribution boards/switch boards, terminated thereto.  These conductors shall be of such size and material as specified.  Depending upon their size and material, the protective earth conductors shall be either drawn inside the conduits along with the cables, or shall be laid external to the conduits.  When laid external to the conduits, this shall be properly clamped with the conduit at regular intervals.

(3). The protective conductors shall be terminated properly using earth studs, earth terminal block etc. as the case may be

(4). Gas or water shall not be used as protective conductor (earth medium).

Table I. Maximum number of PVC insulated 650/1100 V grade aluminium/copper conductor cable conforming to IS: 694-1990 [Clause 16.4.2.1(ii)]

Nominal cross sectional area of conductor in sq.mm

20 mm

25 mm

32 mm

38 mm

51 mm

64 mm

 

S

B

S

B

S

B

S

B

S

B

S

B

1

2

3

4

5

6

7

8

9

10

11

12

13

1.50

5

4

10

8

18

12

-

-

-

-

-

-

2.50

5

3

8

6

12

10

-

-

-

-

-

-

4

3

2

6

5

10

8

-

-

-

-

-

-

6

2

-

5

4

8

7

-

-

-

-

-

-

10

2

-

4

3

6

5

8

6

-

-

-

-

16

-

-

2

2

3

3

6

5

10

7

12

8

25

-

-

-

-

3

2

5

3

8

6

9

7

35

-

-

-

-

-

-

3

2

6

5

8

6

50

-

-

-

-

-

-

-

-

5

3

6

5

70

-

-

-

-

-

-

-

-

4

3

5

4

Note: 1) The above table shows the maximum capacity of conduits for a simultaneous drawing in of cables.

2) The columns headed ‘S’ apply to runs of conduits which have distance not exceeding 4.25 m between draw in boxes and which do not deflect from the straight by an angle of more than 15 degrees.  The columns headed ‘B’ apply to runs of conduit which deflect from the straight by an angle of more than 15 degrees.

3) Conduit sizes are the nominal external diameters.

Table 2. Girder clips or clamps    [Clause 16.4.2.2 (iv)]

Size of conduit

Width

Thickness

i)

20 mm

19 mm

0.9 mm (20 SWG)

ii)

25 mm

19 mm

0.9 mm (20 SWG)

iii)

32 mm & above

25 mm

1.2 mm (18 SWG)

16.5 SPECIFICATIONS FOR NON - METALLIC CONDUIT WIRING SYSTEM

16.5.0 Scope - This chapter covers the detailed requirements for wiring work in non-metallic conduits.  This chapter covers both surface and recessed types of wiring work.

16.5.1 Application

16.5.1.1 Recessed conduit work is generally suitable for all applications.  Surface conduit work may be adopted in places like workshops etc. and where recessed work may not be possible to be done.  The type of work shall be as specified in individual works.

16.5.1.2 Flexible non-metallic conduits shall be used only at terminations, wherever specified.

16.5.1.3 Special precautions.

(1) If the pipes are liable to mechanical damages, they should be adequately protected.

(2) Non-metallic conduit shall not be used for the following applications:-

(a) In concealed / inaccessible places of combustible construction where ambient temperature exceeds 60 degrees c.

(b) In place where ambient temperature is less than 5 degrees c.

(c) For suspension of fluorescent fittings and other fixtures.

(d) In areas exposed to sunlight.

16.5.2 Materials

16.5.2.1 Conduits

(1) All non-metallic conduit pipes and accessories shall be of suitable material complying with IS: 2509-1973 and IS: 3419-1976 for rigid conduits and IS: 6946-1973 for flexible conduits.  The interior of the conduits shall be free from obstructions.  The rigid conduit pipes shall be ISI marked.

(2) The conduits shall be circular in cross-section.  The conduits shall be designated by their nominal outside diameter.  The dimensional details of rigid non-metallic conduits are given in Table 3.

(3) No non-metallic conduit less than 20 mm in diameter shall be used. 

(4)  Wiring capacity - The maximum number of PVC insulated aluminium/copper conductor cables of 650 / 1100V grade conforming to IS: 694-1990 that can be drawn in one conduit of various sizes is given in Table-I under clause 16.4.2.1(2).  Conduit sizes shall be selected accordingly.

16.5.2.2 Conduit accessories

(1) The conduit wiring system shall be complete in all respect including accessories.

(2) Rigid conduit accessories shall be normally of grip type.

(3) Flexible conduit accessories shall be of threaded type.

(4).  Bends, couplers etc. shall be solid type in recessed type of works, and may be solid or inspection type as required, in surface type of works.

(5) Saddles for fixing conduits shall be heavy gauge non-metallic type with base.

(6). The minimum width and the thickness of the ordinary clips or girder clips shall be as per Table 4.

(7) For all sizes of conduit, the size of clamping rod shall be 4.5 mm (7 SWG) diameter.

Outlets

(1) The switch box shall be made of either rigid PVC moulding, or mild steel, or cast iron on all sides except at the front.  The regulator boxes shall however be made only of mild steel or cast iron.

(2) PVC boxes shall comply with the requirements laid down in IS: 5133 (Part-II)-1969.  These boxes shall be free from burrs, fins and internal roughness.  The thickness of the walls and base of PVC boxes shall not be less than 2 mm.  The clear depth of PVC boxes shall not be less than 60 mm.

(3) The specifications for metallic boxes shall be as per requirements of clause 16.4.2.3.

(4) 3 mm thick phenolic laminated sheet covers for all types of boxes shall be as per requirements of clause 16.2.11.3.

16.5.3 Installation

16.5.3. 1 Common aspects for both recessed and surface conduit works

(1) The erection of conduits of each circuit shall be completed before the cables are drawn in.

(2) Conduit joints

(a) All joints shall be sealed / cemented with approved cement.  Damaged conduits pipes/fittings shall not be used in the work.  Cut ends of conduit pipes shall have neither sharp edges nor any burrs left to avoid damage to the insulation of conductors while pulling them through such pipes.

(b) The Engineer, with a view to ensuring that the above provision has been carried out, may require that the separate lengths of conduit etc. after they have been prepared shall be submitted for inspection before being fixed.

(3) Bends in conduit

(a) All bends in the system may be formed either by bending the pipes by an approved method of heating, or by inserting suitable accessories such as bends, elbows or similar fittings, or by fixing non-metallic inspection boxes, whichever is most suitable.  Where necessary solid  type fittings shall be used.

(b) Radius of bends in conduit pipes shall not be less than 7.5 cm.  No length of conduit shall have more than the equivalent of four-quarter bends from outlet to outlet.

(c) Care shall be taken while bending the pipes to ensure that the conduit pipe is not injured, and that the internal diameter is not effectively reduced.

(4) Outlets - All switches, plugs, fan regulators etc. shall be fitted in flush pattern.  The fan regulators can be mounted on the switch box covers, if so stipulated in the tender specifications, or if so directed by the engineer.

(5). Painting - After installation, all accessible surfaces of metallic accessories shall be painted in compliance with clauses under chapter on “Painting”.

16.5.3.2 Additional requirements for surface conduit work

(1) Conduit pipes shall be fixed by heavy gauge non-metallic saddles with base, secured to suitable approved plugs with screws in an approved manner, at an interval of not more than 60 cm, but on either side of couplers or bends or similar fittings, saddles shall be fixed at a closer distance from the centre of such fittings.  Slotted PVC saddles may also be used where the PVC pipe can be pushed in through the slots.

(2) Where the conduit pipes are to be laid along the trusses, steel joists etc. the same shall be secured by means of saddles or girder clips as required by the engineer.  Where it is not possible to use these for fixing, suitable clamps with bolts and nuts shall be used.

(3) If the conduit pipes are liable to mechanical damage, they shall be adequate protected.

16.5.3.3 Additional requirements for recessed conduit work

(1) Making chase

Requirements under clause 16.4.3.3(1) shall be compiled with.

(2). Fixing conduits in chase

(a) The conduit pipe shall be fixed by means of staples, or by means of non-metallic saddles, placed at not more than 60 cm apart, or shall be fixed by any other approved means of fixing.

(b) At either side of the bends, saddles/staples shall be fixed at a distance of 15 cm from the centre of the bends.

(3) Erection in RCC work - Requirements under clause 16.4.3.3(3) shall be completed with.

(4) Fixing inspection boxes - Requirements under clause 16.4.3.3 (4) shall be compiled with.

(5) Fixing switch boxes and accessories - Requirements under clause 16.4.3.3 (5) shall be compiled with.

(6) Fish wire - Requirements under clause 16.4.3.3 (4) shall be compiled with.

(7) Bunching of cables - For ease of maintenance, cables carrying direct current or alternating current shall always be bunched so that the outgoing and return cables are drawn in the same conduits.

16.5.3.4 Earthing requirements

(1) A protective (earth) conductor shall be drawn inside the conduit in all distribution circuits to provide for earthing of non-current carrying metallic parts of the installation.  These shall be terminated on the earth terminal in the switch boxes, and / or earth terminal blocks at the DB’s.

(2) Protective conductors of large size, which may not be possible to be carried inside the conduits (as in the case of some sub-mains etc.), may be laid external to the conduits and clamped thereto suitably.

(3) Gas or water pipes shall not be used as protective conductors (earth medium).

Table 3.  Dimensional details of rigid non-metallic conduits. [Clause 16.5.2.1(2)]

Sl.No. 1 2 3 4 5
Nominal outside diameter
(in mm.)
20 25 32 40 50
Maximum outside diameter
(in mm.)
0.3
20
0.3
25
0.3
32
0.3
40
0.3
50
Minimum inside diameter
(in mm.)
17.2 21.6 28.2 35.8 45
Maximum permissible eccentricity (in mm.) 0.2 0.2 0.2 0.2 0.4
Maximum permissible ovality
(in mm.)
0.5 0.5 0.5 0.5 0.6

Table 4. Ordinary clips or girder clips [clause 16.5.2.2 (VI)]

Size of conduit

Width

Thickness

20 mm & 25 mm

32 mm & above

19mm

25 mm

20SWG   (0.9144 mm)

18 SWG   (1.219 mm)

16.6 SPECIFICATIONS FOR CASING WIRING SYSTEM

16.6.0 Scope - This chapter covers the requirements of casing wiring system using metallic or PVC casing and capping (otherwise also called “wire ways”).

16.6.1 Application

16.6.1.1 Casing and capping wiring is suitable for surface wiring work indoors where necessitated, either due to aesthetics or technical requirements, such as ease of extension of existing wiring, avoidance of recessed wiring in RCC columns etc.  PVC insulated cables and/or other approved insulated cables to IS: 694-1990 shall be used in this type of work.

16.6.1.2 (i) This system using PVC wire ways shall not be adopted in residential buildings, or such other locations where there is a risk of tampering.

(ii) Restrictions of applications on the use of non-metallic conduit as indicated in clause 16.5.1.3. are applicable for PVC casing wiring system as well. 

(iii) Where casing wiring system has to be necessarily adopted in situations under (i) and/or (ii) above, only metallic wire-ways shall be used.

16.6.2 Materials

16.6.2.1 The casing and capping shall be of the same material, viz. either PVC or anodised aluminium, in extruded sections.

16.6.2.2 The casing shall have a square or rectangular body.  The capping shall be slide-in type with double grooving in the case of PVC wire ways, and plain type for metallic wire-ways.  All surfaces shall have smooth finish inside and outside.  The top of the sidewalls of the casing body shall be suitable for the above types of fixing arrangement of capping thereto.

16.6.2.3 PVC casing and capping shall be of good quality PVC, free from defects like deformation, unevenness, blisters, cavities etc.

16.6.2.4 Dimensions

(i) The sizes of casing and capping for the various sizes of cables and the maximum number of 650/1100 V grade PVC insulated aluminium/copper conductor cables that can be carried in one casing are given sizewise in Table V.

(ii) The thickness of the casing and capping shall be 1.2 mm +/- 0.1 mm.

16.6.2.5 Outlet boxes - The outlet boxes such as switch boxes, regulator boxes and their phenolic laminated sheet covers shall be as per requirements under clause 16.4.2.3.

16.6.3 Installation

16.6.3.1 Attachment to wall and ceiling

(i) The casing shall be fixed by means of suitable flat head screws to approved type of asbestos or fibre fixing plugs, at intervals not exceeding 60 cm for all sizes.  On either side of the joints, the distance of the fixing arrangement shall not exceed 15 cm from the joint.  Screw head shall be counter sunk within the centre of the casing.  Alternatively, round-headed screws may be used.

(ii) All casing shall be fixed directly on wall or ceiling as above.

(iii) Casing shall be used only on dry walls and ceiling, avoiding outside walls as far as possible, and shall not be buried in walls, nor fixed in proximity to gas, steam or water pipes, or immediately below the latter.

(iv) Casing under steel joists shall be secured by MS clips of not less than 1.2 mm (18 SWG) thickness and width not less than 19 mm, or by approved clamps.

16.6.3.2 Passing through floors or walls - When conductors pass through floors, the same shall be carried in an approved PVC conduit, or heavy gauge steel conduit properly bushed at both ends. The conduit shall be carried 20 cm above floor level and 2.5 cm below ceiling level and neatly terminated into the casing. Steel conduit pipes wherever accessible shall be securely earthed.

16.6.3.3 Joints in casing and capping

(i) The wireways in straight runs should be in single piece as far as possible so as to avoids joints.

(ii) All joints shall be scarfed or cut diagonally in longitudinal section, and shall be smoothed down by filing to make the joints a very close fit as far as possible and without burrs.  They shall be screwed at joints with two or more screws as would be necessary. 

(iii) Joints in capping shall not overlap those in casing.

(iv) Joints arising out of bends or diversions shall be done using standard accessories like elbows, tees, 3 way/4 way junctions etc. of high grade PVC/aluminium alloy (as the case may be), or by suitably cutting the wire-ways and filing them to have a reasonably gap less butt joints.   In no case, the radius of curvature of the cables inside a bend shall be less than 6 times their overall diameter.

16.6.3.4 Casing to harmonize with décor

(i) When the wiring is to be done over an ornamental work with which it is required to harmonize, the design of any special accessories, which may be necessary, shall be submitted to the engineer for approval before use on the work.

(ii) Casing attached to ceiling shall be carried completely across the ceiling/wall whenever required by the engineer, instead of being stopped at an outlet location, and in all such cases, dummy casing must be provided.

16.6.3.5 Attachment of capping

(i) Wherever required by the engineer, capping shall not be fixed until the work has been inspected with the wires in position and approved.  The inspection will be done from time to time as the work progresses.

(ii) Capping shall be attached to casing in individual sections only after all the insulated wires are laid inside.

(iii) No screws or nails shall be used for fixing PVC capping to the casing.

(iv) Metallic capping shall be fixed by using cadmium plated flat head/round head screws in a staggered manner with an axial spacing not exceeding 30 cm.

16.6.3.6 Installation of cables

(i) For ease of maintenance, cables carrying direct current or alternating current shall always be bunched so that the outgoing and return cables are drawn in the same casing.

(ii) Necessary clamps shall be provided to hold the wires inside the casing at suitable intervals, so that at the time of opening of the capping, the wires may remain in position in the casing and do not fall out.

16.6.4 Earth continuity

(i) A protective (earth continuity) conductor shall be drawn inside the casing and capping for earthing of all metallic boxes of the installations as well as for connections to the earth pin of the socket outlets.

(ii) In the case of metallic casing and capping, there shall be a metallic link between adjacent casings with screw connections, and also connections from the end casing to the earth terminal of metallic boxes/outlets/switch boards as the case may be, for complete body earthing of the system.

Table - V Maximum number of PVC insulated 650/1100 volt grade aluminium/copper conductor cable conforming to IS: 694-1990. [Clause 16.6.2.4 (i)]

Nominal cross sectional area of conductor in sq. mm.

10/15 mm x 10 mm

20 mm x 10 mm

25 mm x 10 mm

30 mm x 10 mm

40 mm x 20 mm

50 mm x 20 mm

1.5

3

5

6

8

12

18

2.5

2

4

5

6

9

15

4

2

3

4

5

8

12

6

-

2

3

4

6

9

10

-

1

2

3

5

8

16

-

-

1

2

4

6

25

-

-

-

1

3

5

35

-

-

-

-

2

4

50

-

-

-

-

1

3

70

-

-

-

-

1

2

Note: - Dimensions shown above are outer dimensions of casing.

16.7 SPECIFICATIONS FOR BUS BAR CHAMBERS, RISING MAINS, BUS TRUNKING, AND OVERHEAD BUS BAR SYSTEM

16.7.0 Scope - This section covers the general requirements of busbar chambers, rising mains, bus trunking and overhead busbar system and their busbars, for medium voltage electrical distribution applications.

16.7.1 Bus bar chambers

16.7.1.1 Application -The busbar chambers covered in this chapter are for application in industrial type indoor switch panels.

16.7.1.2 Materials

16.7.1.2.1 Enclosure - The materials for the enclosure shall be in accordance with clause 16.7.1.3.1, depending on the type of fabrication adopted.

16.7.1.2.2 Busbars

(i) Busbars shall be made of wrought aluminium or aluminium, alloy, or electric grade copper, conforming to relevant Indian Standard, as specified.  The ratings of the busbars shall be 100A, 200A, 300A, 400A, 500A, 600A, or 800A as specified.

(ii) Busbars shall be of sufficient cross-section so that a current density of 130A/sq.cm (800A/sq.inch) is not exceeded at nominal current rating for aluminium bus bars, and 160A/sq.cm (1000A/sq.inch) for copper busbars. The minimum sizes of sections of busbars are given in Table VI.

(iii) The cross section of the neutral busbar shall be the same as that of the phase busbar for busbars of capacity up to 200A; for higher capacities, the neutral busbar must not be less than half the cross-section of that of the phase busbar.

(iv) The busbars shall be suitably insulated with PVC sleeves/tapes.

Table VI Aluminium / Copper bus bar sections (Clause 16.7.1.2.2)

Current ratings in amps. upto

Recommended rectangular cross-section

Aluminium

Copper

No. of strips / phase

Size in mm

No. of strips / phase

Size in mm

100

1

20 x 5

1

20 x 3

200

1

30 x 5

1

25 x 5

300

1

50 x 5

1

40 x 5

400

1

50 x 5

1

50 x 5

500

1

75 x 5

1

60 x 6

600

1

80 x 6

-

-

1000

1

100 x 10

-

-

1200

1

125 x 10

-

-

1600

2

100 x 10

-

-

2000

2

125 x 10

-

-

2500

3

125 x 10

-

-

Note: i) In larger busbars of sizes above 1000 amps, the sections can be accepted in other rectangular cross-sections and numbers also, provided the total cross-sectional area offered is not less than the total cross sectional area shown in the above table against the respective busbar rating.

ii) With aluminium busbars, only aluminium wire/solid bar connections shall be made for incoming/ outcoming mountings on the switchboards.

iii) With copper busbars, only copper wire/solid bar connections shall be made for incoming/ outcoming mountings on the switchboards.

  1.  

Busbar supports

(i) Busbar supports shall be made from a suitable insulating material such as non- hygroscopic phenolic laminated sheet, porcelain or other non-hygroscopic insulator conforming to relevant Indian Standards.

(ii) The support shall be sufficiently robust and spaced to effectively withstand Electro mechanical stresses produced in the event of short circuits.

(iii) Hardware used for mounting the busbar supports to the enclosure shall be cadmium-plated iron/GI.

Construction

16.7.1.3.1 Enclosure

(i) Busbar chamber shall be fabricated with MS angles for framework and covered all around with sheet steel of thickness not less than 1.5 mm in a box form.  Front covers of the busbar chambers shall be detachable and cover (s) on the remaining sides may or may not be detachable as may be specified.  The covers shall be fitted with dust excluding gasket, secured with sufficient number of cadmium plated iron screws to ensure that the covers are dust tight.  Suitable openings shall be provided for cable /conduit entries are required.  Bus bar chambers are busbars of more than 90 cm length shall have horizontal and vertical stiffeners welded to main frame. 

(ii) Alternatively, the busbar chamber shall be made of sheet steel of thickness not less than 3 mm with detachable covers and dust excluding gaskets.  The joints shall be continuous welded.  The detachable cover(s) shall be secured to the box with sufficient number of cadmium plated iron screws.  This type of busbar chamber shall be restricted for busbars up to 90 cm length. 

(iii) Bus bar chambers for busbars up to 90 cm length shall have detachable end covers so that the same can be extended.

(iv) Two numbers of GI earth studs of appropriate size with double washers shall be provided on the body of the enclosure the terminals shall be permanently marked ‘E’ or

(v) The enclosure shall be painted with one coat of primer paint after cleaning the surface, and after de-rusting and degreasing.  Two coats of finished paints shall be done in shall thereafter be applied by spray painting process.  This shall be done in works before bringing the material to the site. 

16.7.1.3.2 Supports - Busbars shall be rigidly fixed to the supports, if of porcelain or of SMC /DMC solid block type base. Busbars shall be firmly held within the slots in sheet type supports, which in turn shall be rigidly fixed to the chamber.

16.7.1.3.3 Clearances - The minimum clearances to be maintained for enclosed indoor air insulated busbars for medium voltage applications shall be as follows:

Between

Min. clearances

Phase to earth

26 mm

Phase to phase

32 mm

16.7.1.3.4 Arrangement of bus bars and main connections - Busbars and main connections which are substantially in one plane shall be arranged in the order given below:-

(i) A. C. System

  1. The order of phase connections shall be red, yellow and blue.

(b) When the run of the conductors is horizontal, the red shall be on the top, or on the left, or farthest away as viewed from the front.

(c) When the run of the conductors is vertical, the red shall be on the left, or farthest away as viewed from the front. 

(d) When the system as a neutral connection in the same plane as the phase connections, the neutral shall occupy the bottom position, if horizontal, and extreme right if vertical  or nearest position when viewed from the front.

(e) Unless the neutral connection can be readily distinguished from the phase connections, the order shall be red, yellow, blue and black. 

(ii) D. C. System

(a) When the run of the conductor is horizontal, the red shall be on the top, or on the left, or farthest away from the front.

(b) When the run of the conductors is vertical, the red shall be on the left, or farthest away as viewed from the front.

(c) When the system is three wire with the conductors in the same plane, the neutral shall occupy the middle position. 

16.1.7.3.5. Bus bar marking – Bus bars and main connections shall be marked by colour or letter as per Table VII.

Table VII.   i). Marking of bus bars and main connection (Clause 16.7.1.3.5)

Bus bar and main connection

Colour

Letter/ Symbol

i)

Three phase

Red, Yellow, Blue

R.Y.B.

 

Two phase

Red, Blue

R.B

 

Single phase

Red

R

ii)

Neutral connection

Black

N

iii)

Connection to earth

Green

E

iv)

Phase variable (such as connections to reversible motors)

Grey

Gy

ii) For D.C. bus bars and main connections

Bus bar and main connection

Colour

Letter/ Symbol

i)

Positive

Red

R or plus

ii)

Negative

Blue

B or minus

iii)

Neutral connection

Black

B

iv)

Connection to earth

Green

N

v)

Equalizer

Yellow

Y

vi)

Phase variable (such as connections to reversible motors)

Grey

Gy

16.7.1.4 Installation

16.7.1.4.1 Bus bar chamber - Bus bar chambers shall be installed on fixed type switchboards with GI bolts and nuts.

16.7.1.4.2 Connections

(i) Connections to bus bars shall be made either by clamping arrangement, or by bolts and nuts as required.  Tapped holes with studs may be permitted only for copper bus bars for tapping conductor size up to 16 sq.mm.

(ii) All connections shall be made such that there is a clear metal to metal area contact at the tapping so that the current density of the bus bars at the point of connections does not exceed permissible limits, avoiding local heating.

(iii) For tap-off connections from bus bars, PVC insulated wiring cables may be used for current capacity up to 100A, and for higher current capacities, solid conductors/strips suitably insulated with PVC sleeve/tape shall be used.

(iv) The bolts and nuts used for connections to bus bars shall be of aluminium alloy, tinned forged brass or galvanised iron.  Suitable precaution shall be taken against heating due to bi-metallic contact.  Spring washers and plate washers, shall be used with the studs/nuts to ensure proper contact pressure. 

16.7.1.4.3 Earthing - Earthing terminals on the bus bar chamber enclosure shall be connected to the earth bar of the switchboard on which it is installed by protective conductors.

16.7.1.4.4 Miscellaneous

(i) There shall be no hole or opening left on the bus bar chamber so as to prevent entry of insects inside.

(ii) MV Danger Notice Board shall be provided on the front cover, duly fixed by four screws.

(iii) Commissioning - Before connecting mains supply after installation, pre-commissioning checks comprising Megger test, checking the tightness of connections, body earth connection etc. shall be carried out and recorded.

16.7.2 Rising mains

16.7.2.1 Application

(i) The rising mains are essentially used in electrical distribution system in multistoried buildings.  These are only for indoor applications.

(ii) Tap-off arrangements shall be provided on the rising mains with tap-off boxes, and distribution boards, with or without isolators for individual control for further distribution.  The requirements shall be specified.

16.7.2.2 Materials

16.7.2.2.1 Enclosure

(i) The enclosure shall be made from sheet steel of 2 mm thickness for the side channels, and 1.6 mm thickness for the front an back covers.

16.7.2.2.2 Bus bars - The bus bars shall comply with clause 16.7.1.2.2 except that the ratings of the bus bars shall be 200A, 300A, 400A, 600A or 800A as specified.  Each bus bar shall be individually insulated by means of PVC sleeves except at the tap-off portions.

16.7.2.2.3 Bus bar supports - Bus bar support insulators shall be made of non-hygroscopic, non-combustible, track resistant and high strength FRP/SMC/DMC material, and shall be of suitable size and spacing to withstand the dynamic stresses due to short circuit currents.

(i) The accessories used with the rising mains for tapping and distribution shall be as per clause 16.7.2.4.2.

(ii) Tap-off boxes shall be suitable for mounting over the rising mains.  The rating shall be 32A, 63A, 100A or 200A, as specified.

Construction

16.7.2.3.1 Enclosure

(i) The rising mains shall be manufactured in convenient sections to facilitate easy transportation and installation.  The sections shall be connected to form a vertical run at site.  Each section shall be provided with suitable wall straps at convenient intervals for fixing to the wall. 

(ii) The enclosure shall be sturdy so as to withstand the internal and external forces resulting from the various operating conditions.

(iii) The front covers shall be detachable.  Neoprene gaskets shall be [provided between the covers and the side channels.

(iv) The entire rising mains shall be designed for dust, and vermin proof construction.  The enclosure shall have a degree of protection not less than IP 42 in accordance with IS: 2147.

(v) Built-in fire proof barriers shall be provided to restrict the spread of fire through the rising mains from one section to the adjacent section.

(vi) Necessary provisions for ventilation shall be made at suitable intervals.  These shall be complete with welded non-ferrous metallic mesh to prevent entry to vermin. 

(vii) Two numbers of GI earth strips of appropriate size shall be provided along side the rising main enclosure, and shall be bolted to each section of the rising mains.

(viii) Painting of the rising main enclosure along with their mountings shall be done as per clause 16.7.3.1(v) of these specifications.

16.7.2.3.2 Bus bars and supports

(i) The clearance for the bus bars shall be as per clause 16.7.1.3.3 of these specifications.

(ii) (a) Bus bar joints shall be thoroughly cleaned and a suitable oxidizing grease shall be applied before making the joint.

(b) High tensile bolts, plain and spring washers shall be provided to ensure good contact at the joints.

(b) The overlap of the bus bars at the joints shall be not less than the area of the cross section of the bus bars.

(iii) Expansion joint made of aluminium strips shall be provided wherever necessary, to take care of expansion and contraction of the bus bars under normal operating conditions.  This shall be invariably provided whenever the length of the rising mains exceeds 15 m.

(iv) (a) the bus bars shall be provided with thrust pads so that the expansion of the conductors is upwards only.

(b) The bus bar clamps and insulators shall be designed to withstand the forces due to short circuit current.  They shall also permit free vertical movement of the bus bars during expansion and contraction.

Installation

16.7.2.4.1 Installation of rising mains

(i) Rising mains shall be installed on walls, to which the foundation bolts shall be suitably grouted.  The contractor without extra payment shall provide the foundation bolts.

(ii) The floor openings in the building slabs shall be closed as per 16.1.14 (iii).

  1.  

(i) Tap-off boxes shall be located at specified intervals and shall be installed at a height of 1.5 m to 2 m above the floor level.  These shall be permanently connected to the bus bars of the rising mains.

(ii) Distribution fuse boards, where specified, shall also be provided, besides the tap-off boxes.  The distribution boards shall be complete with ISI marked HRC fuse links of the specified rating.  The rating shall be 32A, 63A, 100A or 200A as specified.

Note: Where specified, independent MCBDB’s should be provided for distribution instead of HRC DB’s as part of the rising mains system.(iii) Isolators, where specified, shall be mounted directly on the rising mains to facilitate isolation of power supply to any desired section.

(iv) An adapter box for connecting to the incoming switchgear shall be provided at the bottom end of the rising mains.

16.7.2.4.3 Earthing - The GI strips (protective conductors) shall be terminated on to the earth terminal/earth bus at the switchboard at the feeding end.  Metallic body of all mountings shall be bonded to these GI strips.  Earth continuity conductor for distribution further shall also be tapped from these.

16.7.2.4.4 The entire installation, including mountings, shall be provided in such a manner that there are no chances of entry of insects into the rising mains.

16.7.2.4.5 Danger notice board - These shall be provided on the rising mains at every floor level.

16.7.2.4.6 The rising mains shall be commissioned as laid down in clause 16.7.1.4.4(iii) of these specifications.

16.7.3 Bus trunking

16.7.3.1 Application - These are generally provided for interconnections between the transformers over 500 KVA / DG sets over 300 KVA, and their switch board panels, and also for interconnections between large switchboard panels where specified, thereby avoiding use of large sizes of cables for such interconnections.

16.7.3.2 Materials

16.7.3.2.1 Enclosure - Sheet steel of minimum 2mm thickness shall be used for fabricating the enclosure.

16.7.3.2.2 Bus bars and supports - Bus bars and their supports shall comply with clauses 16.7.1.2.2 and 16.7.2.2.3 of these specifications.  The current rating shall be as specified individual cases.

16.7.3.3 Construction

16.7.3.3.1 Enclosure 

(i) The enclosure shall be of bolted type, box type, welded type or any pother type as per the manufacturer’s standard practice, and shall be made out from sheet steel of minimum 2 mm thickness.  The front cover only shall be detachable.  The section of the bus duct shall be rectangular.  The enclosure shall be sturdy so as to withstand the internal and external forces resulting from the various operating conditions. 

(ii) The bus trunking enclosure shall be fabricated in convenient sections for easy transportation and installation.  The sections shall be connected to form horizontal and vertical runs as required at site.  The enclosure shall be provided with flanged ends with drilling arrangement to suit the flanges at the switch gear and transformer terminals.  All flanges shall be provided with gaskets, nuts, bolts, washers, etc.

(iii) The entire bus trunking enclosure shall be designed for dust and vermin proof construction.  The enclosure for outdoor installation shall be additionally in weatherproof construction.  The enclosure shall have a degree of protection not less than IP 42 for indoor application, and IP 54 for outdoor application in accordance with IS:2147.

(iv) Bus trunking, if required to be installed outdoors, shall be provided with a metallic protecting canopy of adequate size above the bus trunking, fabricated as part of the enclosure.

(v) Neoprene gaskets shall be provided to satisfy the operating conditions imposed by temperature, weather etc. and durability.

(vi) Provisions for ventilation shall be made as per clause 16.7.2.3.1(vi) of these specifications.

(vii) Two numbers of GI earth strips of appropriate size shall be provided alongside the bus trunking enclosure and shall be bolted with each section of the bus trunking.

(viii) Painting of the bus trunking enclosure shall be done as per clause 16.7.1.3.1(v) of these specifications.

16.7.3.3.2. Bus bars and supports

(i) The clearances for the bus bars shall be as per clause 16.7.1.3.3 of these specifications.

(ii) (a) The bus bars jointing shall comply with clause 16.7.2.3.2(ii) of these specifications.

(b) Flexible connections shall be provided by braided or multileafed conductors for terminations at transformer bushing and switch gear.

(iii) Expansion joints shall be provided as per clause 16.7.2.3.2 (iii) of these specifications

(iv) The bus bar supports shall be fixed such that they withstand the dynamic stresses under short circuit conditions.

Installation

(i) Each section of the enclosure shall be suspended from the ceiling slab with suitable MS suspenders and support angles/channels.  The runs shall be neat and the route shall be as directed by the engineer.

(ii) The bus trunking shall be supported such that its weight does not come on the terminations.

(iii) Danger notice boards shall be provided on the bus trunking enclosure at suitable intervals in every room through which it passes.

(iv) The earthing strips shall be properly terminated to the earth bars at both ends.

(v) Pre-commissioning checks, as peer 16.7.1.4.4(iii) shall be conducted.

16.7.4 Overhead bus bar system

16.7.4.1 Application

(i) The overhead bus bar system is generally used for distribution of power to a number of distributed power loads, such as motors, as in a workshop.  This system has an in-built flexibility for meeting additional loads without many changes in the distribution system.  These specifications cover indoor application only. 

16.7.4.2 Materials

16.7.4.2.1 Enclosure - Sheet metal used for fabrication of side channels shall be 2 mm thick and the top and bottom covers 1 mm thick.

16.7.4.2.2 Bus bars and supports

(i) The bus bars shall comply with clause 16.7.1.2.2 of these specifications.  The bus bars shall however be rated for 200A, 300A, or 400A as specified.  Each bus bar shall be individually insulated by means of PVC sleeves except at tap-off portions.

(ii) The bus bar supports shall comply with clause 16.7.2.2.3 of these specifications.

16.7.4.2.3 Plug-in boxes - The rating of plug-in boxes shall be 32 A, 63 A and/or 100A as specified and shall be complete with ISI marked HRC fuse links, neutral links and double earth connections.

16.7.4.3 Construction

16.7.4.3.1 Enclosure

(i) The enclosure shall be sturdy to withstand the internal and external forces resulting from the various operating conditions. The enclosure shall have a degree of protection not less than IP 42 in accordance with IS: 2147.

(ii) The top and bottom cover plates shall be detachable, and shall complete with gaskets to make the enclosure totally dust and vermin proof.

(iii) The enclosure shall be fabricated in convenient sections for easy transportation and installation.  The bus shall be jointed together with flanges and tie bolts.  Each section of the enclosure shall be suspended from the ceiling slab with suitable and rigid MS suspenders and brackets as required.  Detachable blank sheet steel covers shall be provided for enclosing the free ends of the bus bar run. 

(iv) Two numbers of GI earth strips of appropriate size shall be provided for the complete run of bus bar enclosure and shall be bolted to each section of the bus bar enclosure.  Suitable provision should be made to enable earth connection to the plug-in box, when plugged in.

(v) The painting of the enclosure and the mountings shall be done as per clause 16.7.1.3.1(v) of these specifications.

16.7.4.3.2 Bus bars and supports

(i) (a) The bus bar lengths shall be coupled mechanically, and good electrical contact shall be achieved by bolting together the overlapping ends of the bus bars, and securing the screws with locking plates.

(b) Whenever the bus duct crosses an expansion joint in the building, suitable provision shall be made to allow for expansion as per clause 16.7.2.3.2(iii) of these specifications.

(ii) The bus bar supports shall be designed in such a manner to ensure that the contacts of the plug-in boxes make good electrical connections with the bus bars. 

(iii) The clearances for the bus bars shall be as per clause 16.7.1.3.3 of these specifications.

16.7.4.3.3 Plug-in boxes

(i) Each section of the bus bar enclosure shall have plug-in points spaced at intervals of approximately 600 mm for the insertion of plug-in boxes.

(ii) The plug-in boxes shall be fabricated as compact sheet steel boxes with hinged doors and shall house the fuse holders.  The fuse holders shall be solidly connected to high conductivity copper clip-on contacts and reinforced by spring steel strips.  These clip-on contacts shall plug-in directly on to the bus bars at the plug-in points.

(iii) Two earth points shall be located at the ends of the plug-in boxes.  While inserting these boxes into the plug-in points, the earth points shall engage first in the special earth bushes provided on the underside of the bus bar enclosure before the main contacts are made.  While withdrawing these boxes, the earth contact is maintained even after the main contacts are isolated.

(iv) The plug-in boxes after insertion into the plug-in points shall be fastened by wing nuts.

(v) Each plug-in box shall be fitted with a brass compression gland suitable for the size of the cable specified.  It should be possible to provide this gland in any position, i.e. left hand side, right hand side or lower side of the plug-in box.

 (vi) The unused plug-in points shall be blanked with detachable sheet steel covers.

Installation

16.7.4.4.1 Installation of bus sections

(i) The bus sections shall be jointed together with flanges and tie bolts.  Each section of the enclosure shall be suspended from the ceiling slab with suitable MS suspenders and support angles/channels as required. 

(ii) Bus trunking shall be suspended at a uniform height of about 2.4m above floor level.  The layout shall be got approved from the engineer before erection.  The runs shall be straight, except at points of changes in direction.

(iii) A connector assembly shall be supplied loose with each section of the enclosure for coupling two sections, and it shall comprise a rubber locating ring, busbar insulating tube and a connector insulating tube.

16.7.4.4.2 Earthing - The GI strips of the bus duct shall be connected to the earth bus/earth terminal(s) of the switch board controlling the bus ducts, by appropriate protective conductors, not withstanding the connection by the armouring of the feeder cable.

16.7.4.4.3 Danger notice board- These shall be provided on the enclosure at suitable intervals and not exceeding 5 m.

16.7.4.4.4 This system shall be commissioned after checks as per 16.7.1.4.4(iii).

16.8 SPECIFICATIONS FOR EARTHING

Scope - This section covers the essential requirements of earthing system components and their installation.  This shall be read with Appendix G that lays down criteria for their design.  For details not covered in these specifications, IS code of practice on earthing (IS: 3043-1987) shall be referred to.

16.8.1 Application

(1) The electrical distribution system in the department is with earthen neutral (i.e. neutral earthed at the transformer / generator end).  In addition to the neutral earthing, provision is made for earthing the metallic body of equipment s and non-current carrying metallic components in the sub-station, as well as in the internal/external electrical installations.

(2) Earthing system is also required for lighting protection, computer installations and hospital operation theaters, etc. for functional reasons.

(3) Earthing requirements are laid down in Indian Electricity Rules, 1956, as amended from time to time, and the Regulations of the Electricity Supply Authority concerned.  These shall be compiled with. 

(4) Though this section and Annexure 16-A.7 form part of the Specifications for Internal EI works, these requirements shall be compiled with in works of earthing for other applications also. 

16.8.2 Materials

16.8.2.1 Earth electrodes

16.8.2.1.1 Types -  The type of earth electrode shall be any of the following, as specified.  (For selection criteria in designs, Annexure 16-A.7 may be referred to).

  1. Pipe earth electrode.
  2. Plate earth electrode.
  3. Strip or conductor earth electrode.

16.8.2.1.2 Electrode materials and dimensions

(1) The materials and minimum sizes of earth electrodes shall be as per Table VIII.

(2) GI pipe electrodes shall be cut tapered at the bottom, and provided with holes of 12 mm dia, drilled not less than 7.5 cm from each other up to 2 m of length from the bottom.

(3) The length of the buried strip or conductor earth electrode shall be not less than 15 m.  This length shall suitably be increased if necessary, on the basis of the information available about soil resistance, so that the required earth resistance is obtained.  Prior approval of the engineer shall be taken for any such increase in length.

Table VIII. Materials and sizes of earth electrodes.  [Clause 16.8.2.1.2(I)]

Type of Electrodes

Material

Size

Pipe

GI Medium class

40 mm dia

4.5 mm long

(without any joint)

Plate

(i) GI

60cm x 60cm x 6cm thick

 

(ii) Copper

60cm x 60cm x 3mm thick

Strip

(i) GI

100 sq.mm. section

 

(ii) Copper

40 sq.mm. section

Conductor

(i) GI

5 mm dia (6 SWG)

 

(ii) Copper

4 mm dia (8 SWG)

Note-Galvanisation of GI items shall conform to class IV of IS: 4736-1986.

16.8.2.2 Earthing conductor

(1) The earthing conductor (protective conductor from earth electrode up to the main earthing terminal/earth bus, as the case may be) shall be of the same material as the electrode, viz. GI or copper, and in the form of wire or strip as specified.

(2) The size of earthing conductor shall be specified, but this shall not be less than the following (For calculating the size of the earthing conductor in design, Appendix G may be referred to).

  1. 5 mm dia (6 SWG) for GI, or 4 mm dia (8 SWG) for copper wire,
  2. 25 mm x 4 mm in the case of GI strip, or,
  3. 20 mm x 3 mm in the case of copper strip.

(3) Earthing conductor larger than the following sectional areas need not be used, unless otherwise specified.

  1. 150  sq. mm. incase of GI, or,
  2. 100 sq. mm. In case of copper.

16.8.2.3 Earth bus

(1) Two copper strips, each of size 50 mm x 5 mm shall be provided as earth bus in a 11 KV sub-station and/or diesel generating station irrespective of the capacity of the transformer or the D.G.Set.  Each of these strips shall be connected to an independent earth electrode.  The two earth leads from the body of each transformer/panel/generating set, etc. shall be connected to these two strips of earth bus.  The two strips of the earth bus shall be bonded together.

(2) The neutral earth leads of the transformer and/or generator alternator shall not be connected to this earth bus.  They shall be connected directly to individual earth electrodes.

16.8.2.4 Hardware items - All hardware items used for connecting the earthing conductor with the electrode shall be of GI in the case of GI plate earth electrodes, and forged tinned brass in case of copper plate electrodes.

16.8.2.5 Protective (Earth continuity/Loop earthing) conductor

(1)  The material and size of protective conductors shall be as specified. (2) The minimum cross sectional area of a protective conductor (not contained within a cable or flexible cord) shall be:-

  1. 2 mm dia (14 SWG) in case of copper,
  2. 2.5 mm dia (12 SWG) in case of GI, or,
  3. 2.24 mm dia (13SWG) in case of aluminium.

(3) Unless otherwise specified, GI conductor should not be ordinarily used as protective conductor within any circuit, beyond a DB down stream.

16.8.3 Location for earth electrodes

(1). Normally an earth electrode shall not be located closer than 1.5 m from any building.  Care shall be taken to see that the excavation for earth electrodes may be located further away from the building, with the prior approval of the engineer.

(2) The location of the earth electrode will be such that the soil has a reasonable chance of remaining moist as far as possible.  Entrances, pavements and roadways, should be avoided for locating earth electrodes.

16.8.4 Installation

16.8.4.1 Electrodes

16.8.4.1.1 Various types of electrodes

(1) Pipe electrode shall be buried in the ground vertically with its top at not less than 20 cm below the ground level.  The installation shall be carried out as shown in Fig.4.

(b) In locations where the full length of pipe electrode is not possible to be installed due to meeting a water table, hard soil or rock, the electrode may be to reduced length, provided the required earth resistance result is achieved with or without additional electrodes, or any alternative method of earthing may be adopted, with the prior approval of the Engineer-in-charge.  Pipe electrodes may also be installed in horizontal formation in such exceptional cases.

(2) Plate electrode shall be buried in ground with its face vertical, and its top not less than 3 m below the ground level.

(3) When more than one electrode (plate/pipe) is to be installed, a separation of not less than 2 m shall be maintained between two adjacent electrodes.

(4) The strip or conductor electrode shall be buried in trench not less than 0.5 m deep.

(b) If conditions necessitate the use of more than one strip or conductor electrode, they shall be laid as widely distributed as possible, in a single straight trench where feasible, or preferably in a number of trenches radiating from one point.

(c) If the electrode cannot be laid in a straight length, it may be laid in a zig-zag manner with a deviation up to 45 degree from the axis of the strip.  It can also be laid in the form of an arc with curvature more than 1 m or a polygon.

16.8.4.1.2 Artificial treatment of soil - When artificial treatment of soil is to be resorted to, the same shall be specified in the schedule of work.  Charcoal/coke and salt as indicated in fig.4 and 5 shall surround the electrode. In such cases, excavation for earth electrode shall be increased as per the dimensions indicated in these figures.

 16.8.4.1.3 Watering arrangement

(1).  In the case of plate earth electrodes, a watering pipe 20 mm dia. medium class pipe shall be provided and attached to the electrodes.  A funnel with mesh shall be provided on the top of this pipe for watering the earth.

(2) In the case of pipe electrodes, a 40 mm x 20 mm reducer shall be used for fixing the funnel with mesh.

(3) The watering funnel attachment shall be housed in a masonry enclosure of size not less than 30 cm x 30 cm x 30 cm.

(4) A cast iron/MS frame with MS cover, 6 mm thick, and having locking arrangement shall be suitably embedded in the masonry enclosure.

16.8.4.2 Earthing conductor (Main earthing lead)

(1) In the case of plate earth electrode, the earthing conductor shall be securely terminated on to the plate with two bolts, nuts, checknuts and washers.

(2) In the case of pipe earth electrode, wire type earthing conductor shall be secured as indicated in fig.4 using a through bolt, nuts and washers and terminating socket.

(3) A double C-clamp arrangement shall be provided for terminating tape type earthing conductor with GI watering pipe coupled to the pipe earth electrode.  Galvanised “C” shaped strips, bolts, washers, nuts and checknuts of adequate size shall be used for the purpose.

(4)The earthing conductor from the electrode up to the building shall be protected from mechanical injury by a medium class, 15 mm dia.  GI pipe in the case of wire, and by 40mm dia, medium class GI pipes in the case of strip. The protection pipe in ground shall be buried at least 30 cm deep (to be increased to 60 cm in case of road crossing and pavements). The portion within the building shall be recessed in walls and floors to adequate depth in due co-ordination with the building work.

(5) The earthing conductor shall be securely connected at the other end to the earth stud/earth bar provided on the switchboard by:

  1. soldered or preferably crimped lug, bolt, nut and washer in the case of wire, and,
  2. bolt, nut and washer in case of strip conductor.

In the case of substations or alternators, the termination shall be made on the earthing terminal of the neutral point on the equipment and/or the earth bus, as the case may be.

16.8.4.3 Earth bus and main earthing terminal

(i) In case of substations and generating stations, two numbers copper/GI (as specified) earth bus shall be provided, duly connected to two numbers of independent electrodes, exclusively for equipment (body) earthing of substation or generating station equipment.

(ii) In all other installations, main earthing terminal shall be provided at the main switchboard.  This may be in the form of earth stud or single earth bar depending on the type of the switchboard.

(iii) Following conductors shall be terminated on to the main earthing terminal.

  1. Earth connection from electric supply company (where provided).
  2. Earthing conductor from electrode.
  3. Protective conductors.
  4. Equi-potential bonding conductors.

16.8.4.4 Protective (loop earthing/earth continuity) conductor

(i) Earth terminal of every switchboard in the distribution system shall be bonded to the earth bar/terminal of the upstream switchboard by protective conductor(s).

(ii) Two protective conductors shall be provided for a switchboard carrying a 3 phase switch gear thereon.

(iii) All the mountings of industrial type switchboards shall be bonded to the earth stud/earth bar using a protective conductor looping from one to another.  Loop earthing of individual units will not be however necessary in the case of cubicle types switchboards.

(iv) The earth connector in every distribution board (DB) shall be securely connected to the earth stud/earth bar of the corresponding switchboard by a protective conductor.

(v) All metallic switch boxes and regulator boxes in a circuit shall be connected to the earth connector in the DB by protective conductor (also called circuit protective or loop earthing conductor), looping from one box to another up to the DB.

(vi) The earth pin of socket outlets as well as metallic body of fan regulators shall be connected to the earth stud in switch boxes by protective conductor.  Where the switch boxes are of non-metallic type, these shall be looped at the socket earth terminals, or at an independent screwed connector inside the switch box.  Twisted earth connections shall not be accepted in any case.

(vii) Double earthing strips in rising mains, bus trunking etc. shall be securely connected to the earth bar/earth stud at the sending end switchboard.  In the case of overhead busbar systems, protective conductors shall be provided in addition to feeder cable armouring connection.

16.8.5 Earth resistance

(1) The earth resistance at each electrode shall be measured.  No earth electrode shall have a greater ohmic resistance than 5 ohms as measured by an approved earth testing apparatus.  In rocky soil the resistance may be upto 8 ohms. 

(2) Where the above stated earth resistance is not achieved, necessary improvement shall be made by additional provisions, such as additional electrode(s), different type of electrode, or artificial chemical treatment of soil etc., as may be directed by the Engineer-in-charge.

16.8.6 Marking

(1) Earth bars/terminals at all switchboards shall be marked permanently, either as “E” or as

(ii) Main earthing terminal shall be marked “SAFETY EARTH – DO NOT DISCONNECT”.

16.8.7 Use of Residual Current Devices (RCDs) - An extract on selection and application of RCDs (also known as RCCBs) from IS: 12640-1988 is given at Appendix H.  Provision of RCD shall be specified in individual cases keeping in view the type, use, importance, system of earthing and nature of electrical installations to be protected by the RCCBs, requirements of the local electric supply company, etc.  The sensitivity shall be 30 mA, 100 mA, or  500 mA, as specified.

16.10. SPECIFICATIONS FOR PAINTING

This section cover the requirements of painting work in internal electrical installations, carried out manually by brush.  This does not cover spray painting work of factory made items.

16.10.1 Painting work in general

16.10.1.1 Paints - Paints, oils, varnishes, etc. of approved make in original tin to the satisfaction of the engineer shall only be used.

16.10.1.2 Preparation of the surface - The surface shall be thoroughly cleaned and made free from dust or foreign matter before painting is started.  The engineer may inspect the proposed surface before the paint is applied.

16.10.1.3 Application

(i) Paint shall be applied with brush.  The paint shall be spread as smooth and even as possible.  Particular care shall be paid to rivets, nuts, bolts and over-lapping.  Before drawing out in smaller containers, it shall be continuously stirred with a smooth stick, while painting work is taken up. 

(ii) Primer coat of anticorrosive paint shall be given in the case of steel work, after preparing the surface.  In all cases of painting work, finishing shall be with 2 coats of paint in approved shade.

(iii) Each coat shall be allowed to dry out sufficiently before a subsequent coat is applied.

16.10.1.4 Precautions - All furniture, fixtures, glazing, floors, etc. shall be protected by suitable covering.  All stains, smears, splashing, dropping etc. shall be removed.  While painting of wiring etc. it shall be ensured that the painting of wall and ceiling etc. is not spoiled in any way. 

16.10.1.5 Repainting

(i) Painting on old surface in indoor situations will not include primer coat except where specially mentioned in the tender documents.  However, where rust has formed on iron and steel surfaces, the spots will be painted with one anti-rust primer coat, after preparing the surface.

(ii) In cases of repainting, the old paint shall be removed by first scrapping, or by applying a suitable solvent, and thereafter a fresh coat of the paint shall be applied.

16.10.2 Painting of wood batten - All wood batten shall be given, before erection on all sides, two coats of varnish, made up of not less than 1.36 kg of pure shellac per 4.55 litre of spirit conforming to IS: 347-1975.  The completed installation should be given two coats of paint so that the wiring may match with the surroundings, whenever specified in the tender documents.

16.10.3 Painting of conduits and accessories

(i) Requirement of painting of metallic conduits before installation on surface shall be met as per clause 16.4.3.2(i).

(ii) Requirement of painting of metallic boxes shall be as per clauses 16.4.2.3(ii) and 16.4.3.1(iv).

(iii) After installation in surface or recess, all accessible surface of metallic conduit pipes and fittings, switch boxes and regulator boxes etc. shall be painted with two coats of enamel paint of approved shade.

16.10.4 Repainting of ceiling fan by spray painting- The spray painting of ceiling fan shall be done as per following procedure.

(i) Clean the surface free from all foreign and harmful materials as dirt, moisture, greasy dirt, salts, rust etc.  by means of any suitable detergent as required and dry the surface.

(ii) Rub down lightly with waterproof emery paper, if required in case surface is rusty and wipe off the surface using a piece of clean and dry soft cloth.

(iii) Apply one coat of finishing enamel conforming to IS: 2932-1974 uniformly by spraying and allow it to dry.

16.11 SPECIFICATIONS FOR TESTING OF INSTALLATION

Scope - This section describes the details of tests to be conducted in the completed internal electrical installations,, before commissioning.

16.11.1 General

16.11.1.1 Tests - On completion of installation, the following tests shall be carried out:-

  1. Insulation resistance test.
  2. Polarity test of switch.
  3. Earth continuity test.
  4. Earth electrode resistance test.

16.11.1.2. Witnessing of tests - Testing shall be carried out for the completed installations, in the presence of and to the satisfaction of the engineer by the contractor.  Al test results shall be recorded and submitted to the department.

16.11.1.3 Test instruments - The contractor shall arrange all necessary test instruments for the tests if so required by the engineer.

16.11.2 Insulation resistance

16.11.2.1 The insulation resistance shall be measured by applying between earth and the whole system of conductors, or any section thereof with all fuses in place, and all switches closed, and except in earthed concentric wiring, all lamps in position, or both poles of the installation otherwise electrically connected together, a direct current pressure of not less than twice the working pressure, provided it need not exceed 500 volts for medium voltage circuits.  Where the supply is derived from a three wire D.C. or a polyphase A.C system, the neutral pole of which is connected to earth either directly or through added resistance, the working pressure shall be deemed to be that which is maintained between the phase conductor and the neutral. 

16.11.2.2 The insulation resistance shall also be measured between all the conductors connected to one pole, or phase conductor of the supply, and all the conductors connected to the neutral, or to the other pole, or phase conductors of the supply with all the lamps in position and switches in “off” position, and its value shall be not less than that specified in sub-clause 16.11.1.3

16.11.2.3 The insulation resistance in megaohms measured as above shall not be less than 12.5 megaohms for the wiring with PVC insulated cables, subject to a minimum of 1 megaohm.

16.11.2.4 Where a whole installation is being tested, a lower value than that given by the formula, subject to a minimum of 1 megaohm, is acceptable.

16.11.2.5 A preliminary and similar test may be made before the lamps etc. are installed and in this event the insulation resistance to earth should not be less than 25 megaohms for the wiring with PVC insulated cables, subject to a minimum of 2 megaohms.

16.11.2.6 The term “outlet” includes every point along with every switch, except that a switch combined with a socket outlet, appliance or lighting fitting is regarded as one outlet.

16.11.2.7 Control rheostat, heating and power appliances and electric signs may, if required, be disconnected from the circuit during the test, but in that event the insulation resistance between the case or frame work, and all live parts of each rheostat, appliance and sign, shall be not less than that specified in the relevant Indian Standard Specifications, or where there is no such specifications, shall be not less than one megaohm.

16.11.3 Polarity test of switch

16.11.3.1 In a two wire, installation, a test shall be made to verify that all the switches in every circuit have been fitted in the same conductor throughout, and such conductor, or to the non-earthed conductors of the supply.

16.11.3.2 In a three wire or a four wire installation, a test shall be made to verify that every non-linked single pole switch is fitted in a conductor which is labeled, or marked for connection to one of the phase conductors of the supply.

16.11.3.3 The installation shall be connected to the supply for testing. A test lamp shall test the terminals of all switches, one lead of that is connected tot he earth.  Glowing of test lamp to its full brilliance, when the switch is in “on” position irrespective of appliance in position or not, shall indicate that the switch is connected to the right polarity.

16.11.4 Testing of earth continuity path - The earth continuity conductor, including metal conduits and metallic envelopes of cables in all cases, shall be tested for electric continuity.  The electrical resistance of the same along with the earthing lead, but excluding any added resistance, or earth leakage circuit breaker, measured from the connection with the earth electrode to any point in the earth continuity conductor in the completed installation shall not exceed one ohm. 

16.11.5 Measurement of earth electrode resistance

16.11.5.1. Two auxiliary earth electrode, besides the test electrode, are placed at suitable distance from the test electrode (see figure).  A measured current is passed between the electrode ‘A’ to be tested and an auxiliary current electrode ‘C’, and the potential difference between the electrode ‘A’ and auxiliary potential ‘B’ is measured.  The resistance of the test electrode ‘A’ is then given by

        V

R = ------

        I                                  

Where,             

R = resistance of the test electrode in ohms,                      

V = Reading of the voltmeter in volts, 

I = Reading of the ammeter in amps.

16.11.5.2 Stray currents flowing in the soil may produce serious errors in the measurement of earth resistance.  To eliminate this, hand driven generator is used.

If the frequency of the supply of hand driven generator coincides with the frequency of stray current, there will be wandering of instrument pointer.  An increase or decrease of generator speed will cause this to disappear. 

16.11.5.3 At the time of test, the test electrode shall be separated from the earthing system.

16.11.5.4 The auxiliary electrodes shall be of 13 mm diameter mild steel rod driven upto 1 m into the ground.

16.11.5.5 All the three electrodes shall be so placed that they are independent of the resistance area of each other.  If the test electrode is in the form of a rod, pipe or plate, the auxiliary current electrode ‘C’ shall be placed at least 30 m away from it, and the auxiliary potential electrode ‘B’ shall be placed mid-way between them.

16.11.5.6 Unless three consecutive readings of test electrode resistance agree, the test shall be repeated by increasing the distance between electrodes A and C upto 50 m, and each time placing the electrode B midway between them.

16.11.5.7 On these principles, “Megger Earth Tester”, containing a direct reading ohmmeter, a hand driven generator and auxiliary electrodes are manufactured for direct reading of earth resistance of electrodes.

16.11.7 Test certificate - On completion of an electrical installation (or an extension to an installation), a certificate shall be furnished by the contractor, countersigned by the certified supervisor under whose direct supervision the installation was carried out.  This certificate shall be in the prescribed form in addition to the test certificate required by the local Electrical Supply Authorities.

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