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Wednesday, 19 December 2018

Wiring Designs and Estimation

There are many ways by which the design and estimation of the cost of wiring of building are carried out. In this write up, I am going to limit myself to a very simple, quick and yet correct method of handling the wiring of a moderate sized bungalow with layout.

   The first step is to obtain the architectural design of the building, showing the walls (indicating whether solid , perforated or corrugated, e.t.c.) , door and window positions , staircases, wardrobes, e.t.c. the positions of lighting fittings, accessories, stationary appliances, e.t.c. are indicated with familiar graphical symbols which are interpretable by the use of the legend or key adjacent to the design drawing.

   There are many factors besides the convenience of the owner of the building (client) for selecting and positioning the accessories. Safety is considered most important; for example, switches are installed outside bathrooms to keep them out of reach of persons in contact with wet floor because electric shock in such s very low resistance area is fatal.

   Watertight fittings are selected for wet areas and those exposed to rain. Switches in rooms are not to be situated behind doors to avoid occupants having to go through darkness before actuating them. The number of lamps per fuse are arranged not necessarily up to the ratings of the cable feeding them, but spread over more than one fuse way (final sub circuit) to avoid plunging the whole area into darkness when the fuse blows. The position of the fuse box or the consumer unit in this design is not at the garage nest the watt hour meter, but in approximately the centre of the building to facilitate shorter radial runs of final sub circuit cables of normal sizes. It is advisable to install the energy meter and a circuit breaker in the garage or outside it, but in a protective enclosure for easy access by the supply authority meter readers and wiring inspectors.

   Various types of tabulation called schedules e.g. material schedule, labour schedule, branch circuit schedule, are made from the design drawing data to arrive at the grand total of the building
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