The electricity supply reaches your home via an underground or overhead cable. After entering the home, the supply cable is connected to a sealed terminal box called the service head or cut-out. You should never tamper with this. The service head contains the service fuse, which is there to stop appliances from demanding more electricity than the supply cable can safely deliver without overheating. Most modern homes have a service fuse rated at 100 amps, but a 60 or 80 amp fuse is common in older properties. A lower service fuse rating means you can have fewer high-wattage appliances on at once.
Check for Overload
To work out how many high-wattage appliances your fuse rating can carry at one time, add up the wattages of appliances that you tend to use at the same time (maybe cooker, dishwasher, washing machine, tumble dryer, as well as lights). Divide the total by 230 (the voltage) to get the maximum current flow in amps, and check that this does not exceed the service fuse rating.
The Meter
Two cables run from the service head to the electricity meter, which belongs to your electricity supplier and records how much electricity you consume. Modern meters are digital and usage is recorded on a row of figures. Older meters have circular dials.
If your home uses cheap night-rate electricity to supply electric storage heaters, you will have a dual-rate meter and a timer instead of a single meter wired in from the service head. The timer switches the supply from one meter to the other at pre-set times to record usage at the two different rates.
Some meters nowadays are in a locked unit on an outside wall. You and your supplier should each have a key to get access to the meter. Ask your supplier if you need a replacement key.
The Consumer Unit
Two cables called meter tails run from the meter to the centre that distributes power around the home, sometimes referred to as the fuse box but more commonly known nowadays as the consumer unit. This contains the system's main on–off switch. Wiring systems older than about 25 years will have circuit fuses that melt if the circuit is overloaded or short-circuited. More modern systems have a row of switches called miniature circuit breakers (MCBs) that switch off automatically if a fault is detected. Each fuse carrier or MCB distributes electricity to an individual circuit in the house and controls the rate of current delivered to each circuit: a maximum of 5–6 amps for each lighting circuit, 30 amps for circuits to power points for portable appliances, and 40 or 45 amps for the big fixed appliances such as cookers, water heaters, and electric showers.
The Circuits
All circuits start at a fuse carrier or MCB in the consumer unit.
Ring Main Circuit
In modern wiring systems the circuits that connect power points run in a loop connecting each power point in turn, finally returning to the directions round the loop. Each power point on the ring main can have a branch line spur cable connected into its terminals to supply a single or double power point at the other end of the cable. This makes it easy to add extra power points, if you need them, with the minimum of rewiring.
Radial Circuit
In older wiring systems the power point circuit is radial, where the cable delivers electricity to each power point in turn and ends at the last one. Lighting, even in modern systems, runs in radial circuits. Most homes have at least two lighting circuits, since the wattage of all the light bulbs together would overload a single circuit.
Dedicated Circuit
Large, fixed appliances such as cookers and electric showers always have a dedicated circuit, because the amount of power they use is so great that they would overload a shared circuit.
Electricity Supply to Flats
Individual flats within a purpose-built or converted building should each have their own fuse board or consumer unit and independent circuits. In some conversions, however, each flat or bedsit may rely on the building's original systems, which will control supplies from just one point, with usage recorded centrally and billed to one address.
