Dec 272012
 

How to Maintain Household WiringThe electricity supply to a house comes through an underground service cable or, in some rural areas, through overhead wires. It goes into the electricity meter via a service fuse, and then on to the consumer unit. The incoming cable, the service fuse and the meter, all of which should have tamper-proof seals, belong to the supplier, and should be maintained by them.

The meter measures the amount of electricity drawn from the supply. If you use off-peak electricity, for storage radiators for example, you may have an Economy 7 meter which records separately the electricity used during the day and for a seven-hour period at night. Older installations may have two meters, or a white meter.

The householder’s responsibility begins at the consumer unit. This is the up-to-date term for the fuse box, and is the point from which electricity is distributed to the various wiring circuits in the home. Each circuit will be protected by a fuse or miniature circuit breaker (MCB), and some of or all the circuits may also be connected to a residual current device (RCD) which provides additional protection against the worst effects of an electric shock. The consumer unit has a master switch which disconnects all the circuits in the house.

Circuits
The wiring circuits to power points, lights, immersion heaters and so on radiate out from the consumer unit. Thirteen-amp outlet power points are generally supplied by ring mains, where the cable containing the live, neutral and earth wires is connected as a loop starling and finishing at the consumer unit and connected to each of the power points in turn on the way. This means that the current to any outlet can be shared between the two arms of the loop.

Individual outlets, in a garage for example, and supplies to high-power appliances like immersion heaters and cookers, will be wired in radial circuits, where a single cable containing live, neutral and earth wires connects the consumer unit to the outlet. Old installations, with round-pin sockets, may have all the sockets wired as individual radial circuits.

Lights may be wired in loop-in circuits, where the supply cable runs from the consumer unit to each ceiling rose in turn, with a cable running out to the corresponding switch, and finishing at the furthest rose. Alternatively, they may be wired in a junction box circuit, where the supply goes to a series of junction boxes, which are in turn connected to the lights and their switches.

Fixed wiring
Most fixed wiring in the home – the wiring in the circuits described above ЎЄ consists of three solid copper conductors, one each for live, neutral and earth. In high-power cables the live and neutral conductors consist of several copper strands. The live conductor has red insulation, the neutral black, and there’s an overall grey or white insulating sheath. In modern wiring the insulation and sheathing is PVC plastic.

Thirteen-amp power points
Power points are usually supplied by ring mains. The cables representing two arms of the ring are simply connected together in the appropriate terminals of the socket: red to live or L, black to neutral or N and the earth wires to the terminal marked earth.

The exposed earth wires should be covered by green/yellow sleeving. If the socket is on a radial circuit, it will have only one earth cable.

You may find sockets where three cables are connected, with the third cable ЎЄ known as a spur – leading to an additional socket or other outlet.

Other electrical outlets
Although 13-A power points are the most common form of outlet, there are a number of others:

Razor sockets are special outlets which are safe for use in bathrooms, where the Wiring Regulations outlaw ordinary 13-A sockets. They should conform to BS3052.

Switched outlets are commonly used for immersion healers, central heating boilers and electric storage radiators. They have a switch, often with a neon light to show when they’re on, and an outlet for the flex.

Cooker controls have a large switch to isolate electric cookers, and may also include a 13-A socket.

Switches, sockets and other outlets are either flush- or surface-mounted. Flush-mounted fittings have metal boxes recessed into the wall. Surface-mounted fittings use a plastic pattress which is fixed to the surface of the wall.

Earth bonding
All the metal pipework in a house needs to be earthed to prevent it from becoming live if a fault develops. This is called bonding, and increasingly strict standards for bonding have been a feature of recent editions of the Wiring Regulations. Additional (supplementary) bonding is now required for metal surfaces in kitchens and bathrooms, for example. Unless your home has been rewired in the last ten years or so, it’s quite likely that it doesn’t meet current standards for earth bonding. This doesn’t necessarily mean that it’s unsafe, though.

 

 Posted by at 9:13 pm

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