Please note colours in these images are only representative and may not be the exact colours as found in your cables etc.
Please remember when attempting any electrical installations at home that you are obliged to get the completed job tested by a fully qualified electrician and obtain a minor works certificate. Failure to do this may render your house insurance invalid and you may have difficulty selling your home.
We get asked a lot which cable should be used to supply a lighting circuit or which flex to connect a washing machine to so we have produced a project with tables to allow you to see the difference between all of them. Scroll to the bottom for all tools and equipment.
It is vital to remember that values for cables and flexes can change in domestic situations. A cable in an insulated loft space will get hotter, much more quickly, than a cable looped through garage rafters. Please seek professional help if you are in any doubt whatever. As with most formulas in the building trade there are regulations defining specific boundaries for the use of all materials. Factors such as resistance and voltage drop may need to be assessed and taken into consideration when working out cable runs. Electricity is dangerous and each year an average of 10 people die and 756 are seriously injured in accidents involving unsafe fixed electrical installations and appliances in the home (Figures courtesy of BBC)
The term cable, amongst other things, means "an encased group of insulated wires" . A cable is a fairly inflexible (although of course they can be bent) set of wires used to supply the electricity to certain points in your home. Your meter box is supplied through a cable, sockets are supplied by cables and your lights are fed through cables. A cable can carry many wires depending on the job it needs to do. Most domestic cables carry a black wire which is usually for the neutral current, a red wire for a live current and a bare wire to take residual current to earth. This cable is called 2 core and earth. From 1st April this year all colour codes are to change. For details of these changes please see the link to the Institute of Electrical Engineers. In essence, for domestic use, the cable wire colours will change to those of the flex colours. For additional information see www.iee.org/oncomms/pn/betnet/index.cfm
The bare wire, when the cable is used, should be marked by a green and yellow earth sleeve.
Another cable used a lot in domestic lighting is called 3 core and Earth. The extra core (wire) is in a yellow insulating sheath and is used as an extra conductor to carry power between 2 or more switches operating lights.
Special lighting switch cable can be bought. This is called "Twin red core" and is used as switch cable for your lights. Often this is replaced, by electricians, who use an ordinary 2 core and earth cable as a switch cable and place a little red tape around the black wire in the cable. See our project on lights and switches.
A Flex (abbreviation of flexible) is a flexible cable used to carry electricity from a power point to an appliance. Most appliances are portable and in a lot of cases need to move quite a lot (irons, toasters etc) so the cable supplying them, should it twist or bend, needs to become straight again with the minimum of effort.
Different cables and flexes are used for different jobs because they are thicker and can carry more current and have more, or less resistance. Resistance can be seen as electrical friction and the wires in the cable or flex will absorb some of the energy in the current, allowing a little less to reach the target than was sent.
High energy users such as electric showers and immersion heaters are supplied by thicker wires than are radios as the current that the appliance needs is considerably greater.
Cables supplying circuits etc should be used as in the following table.
Please note again that installation of cables depends on the position they are to be in, the temperature of the area or void, the length of the run, the grouping of the points they serve and the type of device (Fuse, RCD etc) by which they are protected. The first table below is for cables which are installed by method 4 "enclosed in an insulated wall" The second table is for cables installed by method 1, "clipped direct". As you can see there is quite a difference in rating so be absolutely sure you are doing the right thing. Also remember that while it is not an offence to make electrical installations yourself, it is an offence to use them without them having been checked by a qualified electrician. Even a simple socket addition now has to have a minor works certificate. Your house insurance may not be valid if you do not comply with the regulations.
Table 1 = Method 4 Encased in insulated wall
|Cable size||Rating in Amps|
Table 2 = Method 1 Clipped Direct
|Cable size||Rating in Amps|
Once again please check and double check that you are sure about what you are doing. It is an offence to install unchecked wiring and your house insurance may not be valid if you do.