What BNBC states regarding the Busbar Trunking System (LT Busduct)?

LT Busbar Trunking (REF. BNBC 2006, VOL 3, SEC 1.3.18.3):

For high rise buildings, LT (0.4KV TP&N) busbar trunking sytem 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 electrical short circuit in one of the cables or sparks, to have a neat distribution system. Most part of the Busbar Trunking are installed vertically. The horizontal portion of the Busbar Trunking usually connects the vertical portion with the Substation LT panel. 

a) Busbar Trunking are specially useful to minimize voltage drop on account of high amperage intermittent loads. 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 minimum number of bends for 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 protection and covered with appropriate weather resistant water proof material. Extreme care need to be taken in these cases for protection against moisture, water and outside weather.

c) Busbar Trunking must not be placed in places which is even slightly exposed to weather/ moisture/ spray or sprinkle of water.

d) 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 ceiling. Busducts offer 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.

e) Appropriate circuit protection using adequate number of circuit breakers of appropriate rating are needed. In most cases these busducts 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.