All curves shall be maintained by bending the conduit pipe itself with a long radius or by solid type long bends. Fixing of standard bends elbows shall be avoided. Fish steel wire of 16 SWG size shall be provided along with laying of conduit to facilitate drawing of wires in the conduit.
Suitable inspection boxes shall be mounted, flush with the wall ceiling,, at suitable intervals to facilitate drawing and removal of wires. Inspection boxes shall be of cast iron or sheet steel. Suitable ventilating holes shall be provided in the covers of the inspection boxes.
The outlet boxes shall be same as for surface conduit system and shall be mounted flush with the wall ceiling. Selection of-size conductors The size of the conductors of circuits shall be so selected that the drop in voltage from consumers terminals to any and every point on the installation does not exceed three V under the normal conditions ‘The rating of the cable shall be the current which the circuit is designed to carry. The current rating of the cable shall not be less than that of the fuse which protects it. All conductors, switches and accessories shall. Be of such size as to be capable of carrying, without their respective ratings being exceeded, the maximum current which will normally flow through them. Capacity of Sub-Circuits Lights and fans shall be wired on separate sub-circuits. Not more than sub-circuit shall he restricted. to 800 watts. The power sub-circuit shall be designed according to the load requirement of the sub-circuit In no case, more than to outlets shall be provided in a circuit. Passing through walls and floors When the conductors pass through walls, they shall be taken through one piece heavy gauge, rigid steel conduit or porcelain pipe or corrugated PVC pipe extending through the whole thickness of the wall. The ends shall be bushed properly. The pipe shall be of adequate izc so chat’ the wires pass through in a straight line without any twist of cress in wires.
When the pipe extends outside the building, the portion exposed to weather shall be well mounted, turned downwards and property bushed on the open ends. Where owing to irregular coursing or other reasons the plugging of he walls or ceilings with wood plugs presents difficulties, the wood batten metal conduit shall be attached to the wall or ceiling in a manner approved by the Engineer Incharge. Fittings and accessories Ceiling roses and similar attachments - A ceiling rose shall not embody fuse terminals as integral part of it. A ceiling rose or similar attachments shall be used in low voltage installations only. Only one pendent shall be attached to a ceiling rose. Where multiple pendents are to be used, specially designed ceiling roses shall be used. Socket outlet and Plugs Even socket, outlet shall be contv6lled by a switched which shall be on the live side of the line and shall preferably be located immediately adjacent there to or combined therewith. A socket outlet shall not embody fuse terminal as an integral part of it but the fuse may be embodied in plug,
In an earthed system of supply, three pin socket outlet, with the third pin connected to earth, shall be used. The connection from such outlet to any current consuming device shall be done by means of 3 core fixable cords, one end of the earthing core of which shall be connected to the earthing pin and the other to earthing point of the current consuming device. Every plug containing a fuse shall be non-reversible and shall be so arranged and connected that the fuse controls and outer phase conductor or the non-earthed conductor of the circuit.
Ordinary socket outlet shall be fixed at places away from danger of mechanical injury and at a height of not less than 1.25 meters floor level. In case it is to be fixed at a lower height, ‘which shall not be less than 23 cm from flour level, prior approval in writing of Engineer Incharge shall be necessary.
Socket outlet from call shall be fixed as directed by the Engineer-Incharge at height of not less than 1 25 meters above floor level. To carry flexible cord from bell push to socket, concealed conduit from the outlet with a terminal box at 23 cm above floor level may be fixed in the wall. Laying of conduit in slab If required, conduit pipes shall be laid in slab or beam along with reinforcement before concreting. The conduit pipes shall be laid over the bottom reinforcement; the slab of beam unless required otherwise, such that the open face of the outlet box, is flush with the surface of the slab or beam. The conduit pipe shall be fastened securely to the nearest reinforcement with’16 gauge steel wire. The outlet box shall be at-least 63 mm to 75 deep. Cheknuts should be filled with clay h so that concrete in conduit pipe during the concerting. The outlet box shall be filled with clay or Hessian cloth so that the, concrete does not fill in it. All bends shall be made by bending the conduitpipe.
To facilitate drawing of wire in the conduit, 16 SWG fish steel wire shall be provided in the conduit during its erection. Suitable inspection boxes shall be provided flush with the ceiling at suitable intervals to facilitate drawing and removal of wires. Inspection boxes shall be of cast iron or sheet steel, with M.S. cover. Suitable ventilating holes shall be provided in the covers of the inspection boxes. The outlet boxes shall be same as for conduit system and shall be mounted flush with the ceiling. Main switches and Switch boards All main switch gears shall be metal clad and shall be installed in dry situation, as near as practicable to the point of supply. The main switch will have a fuse on each live conductor of supply mains. No fuse shall be provided in the earthed neutral. The neutral wire shall be continuous except at the linked switch gear.
Main switch boards shall be installed in well ventilated rooms or cup-boards or recess having looking arrangements. These boards shall not be installed in damp situations, in. the vicinity of storage batteries, places. exposed to chemical fumes or where inflammable or explosive dust, vapour or gas is likely to be present.
Fixing of switch boards in places likely to be exposed to weather, to drip or to abnormal moist atmosphere, should be avoided. Where it is unavoidable, the outer casing on the switch boards shall be weather-proof and shall be provided with gland or bushings or adopted to receive screwed conduit according to the manner in which cables are run.
The bottom of switch boards shall be more than 1.25 meters above the floor level unless the front of switch boards is completely enclosed by a door or the switch boards is located in a position to which only authorized persons have access.
Equipments which are on the front of a switch boards shall be so arranged that inadvertent personal contract with live part is avoided during the maintenance of switch gear changing of fuse or like operations. The switches shall be so arranged that fuses are pot “alive” when the switch is in the “OFF’ position. A danger notice plate shall be provided on switch boards connected to medium voltage supply and above. Main and branch distribution boards The main and branch distribution fuse boards shall be of meta1 clad type. These shall be of weather proof type for exposed to weather or damp situations and flame proof type for situations exposed to explosive dust vapour or gas.
The boards for mounting metal clad switch gear viz, switch fuse units or distribution boards shall be 9f hinged type with ample space inside the board to accommodate the incoming and out going cables. Main distribution boards shall be controlled either by a linked switch fuse or circuit breaker. Each outgoing circuit shall be provided with a fuse on the phase or live conductor.
Branch distribution boards shall be controlled by a linked switch fuse or circuit breaker. Each outgoing circuits of the branch distribution boards shall be provided with a fuse on the phase or live conductor. The earthed neutral conductor shall be connected to a common link and he capable of being disconnected individually for testing purpose. At least one spare circuit of the same capacity shall be provided on each distribution board. The distribution fuse boards shall be installed as near the centre of load as possible, in dry situation and not exposed to weather. The distribution fuse boards shall be installed as near the centre of load as possible, in dry situations and not exposed to weather.
The distribution fuse boards shall be fixed on suitable stanchions or wall and shall be accessible for replacement of fuses. When two or more distribution fuse boards are connected to different phases of medium voltage supply, these shall either be fixed meters apart or interlocked or arranged so that only one can be opened at a time and the metal case is marked “DANGER” “415 Volts” or installed in a room or enclosure accessible to authorized persons, only. Triple pole distribution fuse boards shall not be used for final circuit distribution for single phase load. Writing of Distribution fuse boards : The load coming on the distribution boards shall be divided, as far as possible, evenly between the number of ways of the boards. One spare circuit should be left for future extension.
All connections between piece of apparatus or between apparatus and terminals on a board shall be neatly arranged in a definite sequence, following the arrangements of the apparatus mounted thereon, avoiding unnecessary crossings. Cables should be connected to terminals only by soldered lugs, crimped lugs, or clamped securely without cutting away the cable strands.
All the conductors shall be rigidly fixed n such a manner that clearance of atIeast 25 mm is maintained between conductors of opposite polarity or phases and between the conductors and any other materials other than insulting material. The incoming and outgoing cables shall be neatly bunched and fixed properly permitting the boards to swing back fully.
If required, pilot lamp connected through an independent switch and fuse shall be provided. The current rating of a fuse shall not exceed the current rating of the fuse carrier or the current rating of the smallest cable in the circuit protected by the fuse. Boards for Mounting switch gear One of the following types of boards shall be used for mounting metal clad switch gear. Hinged type metal boards These types of boards shall be used for low voltage installations for mounting metal clad switch-gear consisting of not more than one switch fuse and one single phase and neutral distribution fuse board. These boards shall consist of a box made of sheet steel not less than 3 mm thick. Alternatively, a-frame of angle iron of minimum size 35 mm x 35 mm x 6 mm or channel of minimum size 25mm x 35mm x 6 mm for these boards shall be made and mild steel plate of 3 mm thickness mounted on the front and 1.6 mm thickness on the back. The joints shall be substantially welded. The boards shall be provided with locking polished teakwood shall be provided at the back. There shall be a clearance of 30 mm minimum between the front and back area covers. No apparatus shall project beyond the edge of the board. No fuse shall be mounted within 25 mm of the board edge. The boards shall be painted with synthetic enamel paint over anti-rust priming coat. The boards shall be securely fixed to the wall by means of rag bolt or wood plugs. Hinged type wooden boards These type of boards shall be used in case of wooden casing or wood batten system of wiring for mounting metal clad switch gear, for use on low voltage installation, consisting of not more than one switch fuse and one single phase and neutral distribution fume board. These boards shall .teakwood board mounted on 25 mm thick well seasoned teakwood batten by means of wood screws. The two halves shall be jointed together by means of at least two number 75 mm long ste1 hinges on one edge and wood screws on the other so as to make a box. The pox shall be provided with a earthing stud. Both the inside and outside of the box shall be painted with two coats of approved varnish irrespective of their being painted to match the surroundings. Where there is danger of attack by white ants, the portion in contact with wall shall be painted with anti-termite paint instead of varnish. No apparatus shall project beyond the edge of the board. No fuse shall be mounted within 25 mm of the edge of the board. The board shall be securely fixed to the wall by means of rag bolts or wood plugs.
Fixed type metal boards: This type of boards shall be used for mounting a large number of switch gear and large capacity metal clad switchgear. These shall consist of angle iron or channel iron frame of suitable size fixed on the wall on the floor and supported on the wall at the top, if necessary. A clear distance of at least one meter shall be provided in front of the switch board. If there are attachments at the back of the board the space behind the switch board shall be either less than 20 cm or more than 75 cm in width measured from the farthest outstanding part of any attachment or conductor. If the space behind the switch board exceeds 77 cm in width, there shall be a passage way from either end of the switch board clear to a height of 1.8 meters. The connection between the switch gear mountings and the outgoing cables upto the wall shall be enclosed in a protective pipe. Fixed type wooden Board This type of board shall be used for small installations connected to low voltage. These shall be made of well seasoned teakwood and may be used as main boards or sub-boards. The joints shell be dovetailed. Both, the inside and outside of boards shall be painted with two coats of approved varnish. The boards shall be securely fixed to the wall by means of rage bolts or wood plugs. For large size medium voltage installation, a drawing showing detailed dimensions, design and disposition of frame work and mountings which shall be arranged neatly systematically to arrive at the overall dimensions shall be submitted for approval of the engineer-Incharge.
These boards may be fixed in recess at least 600, mm x 480 mm x or 40 mm x 480 mm provide in the wall. An R.C.C. lintel of suitable size design arid strength shall be provide above the opening to support the structure above it. The recess shall be finished properly with plaster. The front of the recess shall be provided with a hinged panel of 19 mm thick seasoned teakwood or 19 mm thick solid black board fixed on 65 mm x 20 mm teak wood chaukhat (frame) and shall .be provided with locking arrangement. The chaukhat shall be fixed to the wall hold-fasts of suitable size. The panel and chaukhat shall be well varnished before installation irrespective of their being painted to match the surroundings. Lighting fittings Lights, fans and socket outlets shall, be so located as 10 provide maximum comfort to the occupant and to ci4iblc him to utilize the electricity in the most economical manner. Every lighting fitting shall be controlled by a switch which shall be in live conductor of the circuit. Where control of the fitting at more than one point is necessary. It shall be done by as many two way and intermediate switches as there are control points.
The pendent fittings shall be suspended with twin flexible cords. The maximum permissible weight of pendent fittings suspended from twin flexible cable shah not exceed the following limits. Fittings heavier than 3.5 kg shall Be suspended by chain or rigid steel pipe.
| Lighting fittings | ||
|---|---|---|
| 0.05 | 16/0.2 | 1.7 |
| 0.75 | 24/0.2 | 2.6 |
| 1.00 | 32/0.2 | 3.5 |
The fittings shall be standard models complete with necessary number of tubes and not economical models. These shall be complete with all components supplied as original components with standard models and shall be assembled and wired by the manufacturer at the factory. The fluorescent tube shall be of the same make as the fitting. In cases where tubes are not manufacturer of the fitting, fluorescent tube of any approved make as directed by the Engineer Incharge shall be used. High Pressure mercury / sodium vapour lamps These fittings shall be complete with necessary vapour lamp, lamp holder, fittings with reflector, condenser, choke and starter etc., of appropriate size and quality complete in all respects with electric connections. Lamp Holders All lamp holders shall be bayonet cap type and shall be provided with shade carrier. Outdoor fittings Fittings for external use and for use on roads shall be of a design which shall prevent the entry. of moisture and insects into the fittings. Height of fittings Unless desired otherwise, all wall mounting and pendent fittings inside the building shall be kept at a height of 2.5 meters above the floor level. All fittings outside the building and on roads shall be fixed at the height as directed by the engineer Incharge. Wall mounting brackets shall be fixed on matching well seasoned polished teak wood blocks or boards with brass screws.
Road Pendent fittings shall be suspended with heavy gauge rigid steel conduit pipe duly painted of appropriate size or electroplated steel chains of required length as directed by the Engineer Incharge.
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