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Distribution systems

In large buildings the type of distribution depends on the building type, dimension, the length of supply cables, and the loads.

Power distribution inside large buildings
Power distribution inside large buildings

The distribution system can be divided in to:

  1. The vertical supply system (rising mains)
  2. The horizontal supply (distribution at each floor level)

In most cases a high voltage supply and transformer substation is required. Normally HV switchgear and substation transformers are installed at ground floor (or basement ). However, often there are appliances with large power demand installed on the top floors (converters and motors for lifts, air-conditioning equipment and electric kitchens).

As it is desirable to bringing the high voltage supply as close as possible to the load centers, transformers are installed at the top floor, or if required, additional ones are installed on one of the intermediate floors. In such cases transformers with non-inflammable insulation and cooling are used.

The arrangement of the rising mains depends on the size and shape of the building and suitable size of shafts for installing cables and bus ducts must be provided in coordination with the building architect.

The vertical supply system are implemented in several ways, some of which are: single rising main, grouped supply, individual floor supply, ring main supply, double feed supply and others.

Single Rising Main

Single Rising Main
Single Rising Main

Applications: Where high supply security is not important.


  1. The different loads of individual floors are balanced out
  2. Only a small main L.V board is required
  3. Simple in construction and operation

Disadvantages: Low supply security (a fault in the rising mains effect all floors).

Title:Power distribution inside large buildings – Department of Electrical Engineering – Dr. Hussain Al-Mashat
Size:5.6 MB
Download:Right here | Video Courses | Membership | Download Updates
Power distribution inside large buildings
Power distribution inside large buildings

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