Large Houses, Block of Flats, Offices Distribution Boards

Large Houses, Block of Flats, Offices Distribution Boards Points : large houses, block of flats, offices distribution boards Generally a three phase supply is taken into large houses or blocks of flats. The basic layout will be the same as with a single phase layout, except that with a block of flats there will be a light phase layout, except that with a block of flats there will be a light and power meter for each apartment. Since the three phase supply is 440 volt, special precautions must be taken to prevent shock at medium voltage.

If one lighting distribution fuse board is fed from the Red phase of a 4-wire 440/250 volt a.c. supply, and another is fed from the Blue phase, then if they were near together it might be possible to receive a 440 volt shock if the terminals of both were touched simultaneously. In the same way it is also possible to receive a medium voltage shock at any three phase distribution board or switchgear.

Three alternative precautions to prevent medium volt shock ares (a) The control equipment mush be enclosed in earthed metal or incombustible insulating material, and marked with the voltage present,

or (b) Each item of equipment must be enclosed in earthed metal or incombustible insulating material, and marked with the voltage present.

or (b) All the control equipment must be installed in a locked room accessible only to an authorized person, and the door marked with the voltage present.

The most common precaution is to install all the three phase equipment a locked room. In large houses, a small locked room at the entrance to the servant’s quarters would be a convenient place. In blocks of flats or commercial buildings, the equipment is generally installed in the basement.

Usually all the fuses used in this type of installation are rewireable as they are cheap and easy to replace, but overseas, miniature circuit breakers are used and these are recommended wherever possible (see Section 5 for comparison of protective device’s).

It is most important that in this type of installation, more than one Phase is not taken to any one apartment. Although this seems simple enough in the design and building stages, danger can occur later on when, for example; an extension is built on to one flat and new supplies run in. These supplies may very well be of a different phase, and so if portable appliances are used in that flat, there is a possibility of fatal shock at medium voltage.

Unless the installation is very large, it is preferable to keep all the distribution fuse boards is the control room near the main switches.