An essential part of any building design is determining the right size and type of cable to install for each electrical circuit. The wrong electrical cable size can be wasteful, and in some cases dangerous.
Cables with different thicknesses are used to cope with different amounts of electrical resistance. So, electric cookers, showers, and heaters need thicker cables as they use a large amount of current. And the greater the distance the current has to flow the greater the resistance and the less current available as a result.
Cables placed under insulation and in insulated walls will carry a different rating. And electric cable sizes vary depending on the job they need to do. See how to measure cable size here…
Understanding Basic Terms
An electrical cable is a set of wires that supply electricity to homes and businesses. Cables supply your meter box, sockets, ceilings and wall lights. Most household cables have a blue wire which is neutral, a brown wire for live current, and a bare wire to earth the residual current. This cable is known as a two core and earth, or twin and earth.
An alternative cable used for domestic lighting is called a three core and earth. The extra wire here is used an additional conductor to carry more power between two or more switches operating the lights in an insulating sheath.
Appliance flex in simple terms is a flexible cable. They’re used for appliances that need to be moved around a lot – where a fixed cable would be unsuitable as it may get damaged or crack.
Resistance is electrical fiction where the wires in the cable or flex absorb some of the current energy meaning less arrives at the target destination than was originally sent.
An amp is the base unit of electric current that calculates the electromagnetic force between electric conductors carrying the electric current.
Cable Selection
You need to make sure that your cable has the sufficient current rating for the expected circuit load including a safety margin. The run length of the cable won’t cause a voltage drop of more than 3%, and the properties of the cable are suitable for the installation.
Cables for lighting circuits for domestic purposes are usually a 1.5mm cable. And cables for sockets on a ring or radial main are normally a 2.5mm cable. This measurement is the cross-sectional area of the individual wires within the cable – the actual area of the exposed face of the wire.
The size of the cable should be printed on the sheath. The cross-sectional area of the earth wire in a 1.5mm cable is 1mm. In a 2.5mm cable, the measurement is 1.5mm.
