Introduction to Domestic Electrical Design

The first example of an electrical design is that of a domestic installation, this may seem a strange choice however the modern domestic dwelling has a complex electrical installation, which includes not only the internal lighting and power systems but can also include any or all of the following:- the telephone system, the computer network infrastructure, the aerial distribution system, fire alarm system, intruder alarm system, door entry systems, CCTV, centralised vacuumn cleaning system, exterior lighting, security lighting, eletrically operated gates, electrically operated garage doors, stair lifts, lifts, heating and hot water control system and electric curtains or blinds, it may also incude photovoltaic cells and/or wind turbines which generate electricity for use within the dwelling and for export to the grid.

Because the PESs have a standard maximum demand figure for dwellings there is no fixed reserve capacity therefore there is no need to take into account the creeping load growth mentioned in the load assessment section of this article. PESs normally supply a single phase service to a dwelling with a fuse in the service head of either 80A or 100A which allows a maximum demand of 18.4kVA or 23kVA respectively, if the load is expected to be greater then a three phase supply can be supplied which would increase the allowable maximum demand to 55.2kVA and 69kVA respectively. PESs will of course supply what is requested and will charge for that. Just an observation a 100A house service cut out fuse does not 'blow' at 101A it will not 'blow' until the current reaches 146A and flows at that level for 100,000 seconds, however that figure is the average current at which the fuse will 'blow'. To cater for manufacturing tolerances if 80% of that figure is taken then the maximum allowable demand could rise to 116A or 26.68kVA for a 100A fuse, not good practice to use the higher figures but it may get you out of a problem.

This article is a discussion of the consideration that must be given the various electrical systems within a dwelling, detailed design is covered in the relevant section of the electrical system design section of this website - not yet published.