DOMESTIC ELECTRICAL CIRCUITS National Diploma Mechanical and Electrical Services Construction

Aims and Objectives Aims – To understand the process of delivering an electrical supply around a domestic property. Objectives To understand the basic layout and equipment used within a domestic supply. To investigate the power or ring main circuit. To investigate the lighting circuit used in domestic property.

Electrical cables To supply electricity around the home a series of cables need to be installed, with socket outlets fitted to allow the home user to access the power. All cables must conform to British Standards BS On the 31 st March 2004, the colour code of the cables changed. Prior to this date the colours were red (live) and black ( Neutral) with green for Earth. The colours are now Brown (Live) Blue (Neutral) and green and yellow for Earth. Twin Core and Earth Three Core and Earth Armoured Cable

Electrical Circuits. In a domestic property, the electrical wiring is split into a series of circuits. The two main circuits in a house being a) power sockets known as the ring main. b) The Lighting circuit Each circuit starts at the consumer unit, which splits the main supply into the separate circuits required for each domestic property. A consumer unit, you may also know this as a ‘fuse box’, is placed between the electricity meter and the separate supply circuits situated around the house. The consumer unit is fitted with a series of MCB’s, miniature circuit breakers, which protects each circuit from excessive current.

The Consumer Unit 1. Main incoming Fuse 2. The Suppliers meter 3. The Suppliers Switch 4. Consumer Unit

The Consumer Unit A lot of older properties may still have a fuse box fitted. Each circuit is protected by a fuse, rated from 3 to 40 amp. Once a fuse has been blown, the fuse wire needs to be replaced.

The Consumer Unit Modern properties are now fitted with a consumer unit. These are fitted with MCB’s as opposed to fuses. These just need to be reset, once they have tripped. Each circuit is labelled below each MCB.

Domestic Ring Main

Electrical power is fed through a domestic property via a series of 230 to 240 Volt socket outlets. This circuit of socket outlets is known as a ‘ring main’. The ring is formed by cable leaving the consumer unit, and connecting to each of the socket outlets before returning to the consumer unit. The cable used for this ring main would normally be a 2.5mm² twin core and earth PVC cable. This ring main will then be protected by either a 32 amp fuse or trip device, situated in the consumer unit. Older types of property will be protected by a fused box system. Modern types of property will be protected by a consumer unit that incorporates an RCD (Residual Circuit Device) which will trip, if a fault is detected in the circuit.

Routing Cables Cables in a domestic property are normally hidden within the walls. The cables should be fed vertically to each switch and socket as opposed to diagonally. The type of material used for the floor will determine if cables are fed from Above or below.

Domestic Ring Main Each electrical appliance can then be connected to the ring by pushing a square pinned plug into the socket outlet. This plug is then fitted with a safety device in the shape of a fuse, which is simply fitted into a clip device. Fuses from 3 amp to 13 amp can then be fitted, as required. For electrical appliances that are rated to 750 watts, such as table lamps, Radio’s etc. a 3 amp fuse should be fitted. For larger appliances that are rated to 3000 watts, a 13 amp fuse will be used.

High Power Circuits. As well as normal electrical appliances, we also use electrical equipment that are considered high wattage, or high power users, such as cookers and showers. These appliances cannot be connected to a ring main circuit, and should have there own dedicated circuit, connected to a separate fuse / trip device within the consumer unit. These type of appliances would use a 6sq mm cable, and a 32 amp rated fuse or trip.

Outdoor circuits. At some point homeowners will want to use an electrical appliance out of doors. This may be to mow the lawn, trim the hedge, use a power tool to drill a hole, etc. It is possible to purchase waterproofed sockets suitable for outdoor use. Again these sockets need to be on their own dedicated circuit. For an outdoor circuit the type of cable used would be required to withstand wet weather conditions.

Outdoor circuits When using any appliance outdoors, such as a power tools, there is always a serious risk from electric shocks. Extra protection can be supplied by fitting an RCD to the outdoor socket. These systems are designed to trip at 40 milli seconds, should a fault develop or you cut through a cable. And you should never use electrical equipment in bad weather.

Domestic lighting circuit. In a power circuit, we have a ring main. With lighting we tend to have a live feed from the consumer unit, which is fed to a series of junction boxes. The junction boxes are situated above the plaster ceilings and under floorboards.

Lighting Circuits From the Junction boxes, cables are then attached to the light switches and to the light fittings for each room.