Electricity is supplied to the home through the service cable from the national grid via a local substation. The householder's responsibility for electricity begins at the cables leading from the meter to the consumer unit. Here's how it works.

How does electricity work?

Electricity is a stream of negatively charged particles, called electrons, flowing from negative to positive through a conductor. The flow of electricity is called current, and is measured in amps (A). The driving force, or pressure, of the current is measured in volts (V).

In order for any appliance to function or any bulb to light, electric current must flow in a circuit through the device. Circuits connect all devices in the home to the consumer unit using cable comprising live (red) and neutral (black) copper conductors, covered in plastic insulation.

The consumer unit is connected to the power station, via sub-stations, by a circuit, which carries much higher voltages than the 230V used in the home. All circuits in the home include a third conductor, known as the earth, to provide a safe escape route for electric current in the event of a fault. The earth is also connected to exposed metalwork, such as sinks and taps.

 

Where does electricity come from?

Power is supplied from the power station through the national grid at an extremely high voltage but very low current. This is because energy loss through heat is lower at low currents and high voltages. The electricity is supplied as alternating current (AC) rather than direct current (DC).

This means that the flow of electrons moves backwards and forwards with less energy loss than DC. It is also safer. The speed at which the current alternates is measured in Hertz (Hz). Domestic supplies alternate at 50 times a second, or 50Hz.

 

Safety first!

Household wiring should comply with the requirements of the IEE (Institution of Electrical Engineers) Wiring Regulations, which are published as British Standard BS 7671.

If you plan to carry out any work on your wiring, buy a guide to the Regulations so you can be sure your work meets these requirements. Always leave electrical work to a qualified electrician, unless you are confident you can carry it out safely and correctly.

 

Consumer unit

Consumer unit

All new houses have consumer units instead of the older-style fuse box. However, despite the differences, the basic features remain the same: there is a mains on/off switch and circuit breakers/trip switches or fuses to protect the circuits in the house against overload.

Fuses

The oldest fuse boxes have slot-in rewirable fuse carriers or cartridges. Within each of these is a small length of fuse wire that melts and breaks if it is overloaded. Always keep a supply of replacement wires or cartridges in a range of amp ratings: 5A for lighting, 15A for the immersion heater circuit, and 30A for socket outlet and cooker circuits. Cooker fuses rated at 45A are available only as cartridge fuses.

 

Before doing any electrical work

Turn power off Remove fuse for the circuit you are working on, or turn off the MCB. Make sure everyone else in your home knows you are working on an electric circuit.
Once every three months

Test RCD in consumer unit (and/or any separate versions you might have) Make sure all major appliances are turned off and that everyone else in the house knows the power is to be cut temporarily. Push RCD test button (see left). Switch should flip to the off position. If nothing happens, contact electrician immediately. If switch trips correctly, reset switch to the on position to reconnect power.

 

Fault diagnosis

Mild shock from metal-cased device

Earth fault within item Contact a qualified repairer. This fault should have tripped an RCD, so test yours, or have one fitted if none is present.
 

MCB tripped

Turn off appliances, reset switch and identify faulty device by a process of elimination. Unplug all appliances, then reconnect them one by one to trace cause of problem.

 
Whole house RCD tripped

Reset RCD. If fault occurs again, call qualified electrician.
 

No power

Local power failure Check neighbouring buildings to verify, and report power failure to your electricity company.

Service fuse blown

Call electricity company immediately to replace.
 

Circuit overload

Caused by plugging in too many high-wattage appliances at once. Make sure that you don't overload a circuit – maximum wattage is 7kW.

MCB in consumer unit trips regularly

Faulty device on circuit If an MCB trips when a specific appliance is used, immediately stop using appliance, unplug it and have it checked. If an MCB trips periodically, plug in one appliance at a time to see which one causes the problem. Once you have identified the faulty appliance, have it repaired.

 

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