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BNBC For Electrical Engineers
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1.3.13 Electrical Services Shafts, Bus Ducts, L.T. Riser Cables, and L.T. Busbar Trunking Vertical service shaft for electrical risers
For buildings over six-storey or 20 m high there shall, in general, be a minimum of one vertical electrical service shaft of (200 mm x 400 mm) size for every 1500 m2 floor area.
The electrical service shaft shall exclusively be used for the following purposes:
(a) Electric supply feeder cables or riser mains
(b) Busbar Trunking
(c) telephone cables
(d) Data Cables
(e) fire alarm cables
(f) CCTV cables
(g) Other signal cables
(h) Area fuse/circuit breakers
(i) Floor Distribution boards/sub-distribution boards for individual floors.
The construction of floors of the duct area shall be constructed in such a way so that the remaining empty open space after putting the cables/busbar trunking/ pipes/ conduits in position is filled up with RCC slab(s) or any other non-inflammable material so that fire or molten PVC cannot fall from one floor to the next lower floor(s). For this purpose, arrangements need to be made during floor casting.

Free and easy access to the electrical shaft room on each floor must be available for operation, maintenance, and emergency shutdowns. Vertical cables other than electrical cables shall be placed at a sufficient distance from the nearest electrical cable. A vertical separating brick wall between the electrical and nonelectrical wall is preferable. Vertical Service Shafts for Electrical Risers as mentioned above must not be placed adjacent to the Sanitary Shafts. They should be placed at significant separation in order to ensure that the Vertical Service Shaft for Electrical Risers remains absolutely dry. LT Riser main cables
(a) For low-rise building riser main cables will serve to bring L.T. connection to the floor distribution boards (FDBs) of each floor from the main distribution board. For a 5 storied building or less having a floor space of less than 600 m2 on each floor the riser cables may be PVC insulated cables through PVC or GI pipes.

(b) For bringing the riser main cables a common vertical wall and holes or slots in the floors must be given by the building construction people.

(c) However, for larger floor areas or for higher buildings PVC insulated PVC-sheathed underground cables must be used with protection and spacing.

(d) For more than 9 storied buildings Busbar preferably sandwiched copper busbar trunking should be used for safety reasons.

(e) PVC insulated PVC Sheathed underground cables must be used as Riser Main Cables. These cables shall be placed in or pulled through a PVC pipe of higher diameter so that the cable can be easily pulled through it. The PVC pipes must be fixed vertically in a straight line on the wall of the shaft using appropriate saddles. However, in some cases, PVC-insulated PVC-sheathed underground cables may be directly fixed on the wall using appropriate saddles with 37mm spacing between two adjacent cables. Sheet metal Joint Boxes (with ebonite cover plates) must be placed at each floor tapping point.
(f) The cable work shall be done neatly so that no suspended cables are seen around the place and no suspended flexible pipes are seen.
(g) Each riser cable must have appropriate fuse or circuit breaker protection at the source busbar junction and also at the tap-off point. LT Busbar Trunking
For high-rise buildings, LT (0.4KV TP&N) busbar trunking system is used instead of riser main cables to minimize space in the vertical electrical shaft, to minimize the risk of spreading of fire from one floor to another due to an electrical short circuit in one of the cables or sparks, to have a neat distribution system. Most parts of the busbar trunking shall be installed vertically. The horizontal portion of the busbar trunking shall usually connect the vertical portion with the Substation LT panel.
(a) Busbar trunking is especially useful to minimize space and to minimize risks of spreading fire (during accidents) which may happen with bundles of insulated cables. The conductors supported by insulators inside the busbar trunking shall be copper of solid rectangular cross-section. The copper bars are insulated. A busbar trunking system shall be laid with a minimum number of bends for the distribution system. Typical rating of feeder busbar trunking for 3-phase- 3-wire or 3-phase- 4-wire system shall range from 200 amperes to 3000 amperes although lower amperes are not impossible.
(b) Horizontal busbar trunking of suitable size may be provided along the roads for a group of buildings to be fed by a single substation but with heavy weather (moisture and water) protection and covered with appropriate weather-resistant waterproof material. Extreme care needs to be taken in these cases for protection against moisture, water, and outside weather.
(c) Busbar trunking shall be placed in a dry place and must not be installed in a place that is even slightly exposed to weather/moisture/ spray or sprinkle of water. LT Busducts
In certain applications, especially in factory lighting and factory power distribution of large area factories Busducts are used. In most cases, these Busducts are suspended from the ceiling. Bus ducts offer a safe, reliable, neat distribution system in these cases. The choice will depend on the floor area, type of machinery, type of jobs, and other factors. Appropriate circuit protection using an adequate number of circuit breakers of appropriate rating is needed. In most cases, these bus ducts are horizontally mounted/suspended. The busbars shall be copper. The rating shall depend on the current on each segment and the current carried by each segment.

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