Cables sizes
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Summary: Cable sizes and how to check you are using the right cables for the right job
Cables are used for different applications because they are differing thicknesses and can cope with differing currents safely with differing amounts of electrical resistance. A simple way to explain resistance is to see it as electrical friction.The cable will slow down some of the energy in the current. This means a little less current will reach the target than was actually sent.
Electric cookers, electric showers and Immersion heaters use a great deal of current and therefore require thicker cables. If a cable is too thin for the job it is being asked to do it will get too hot and catch fire. Generally it can be said that any cable carrying current to an appliance that is intended to produce heat will have a bigger current rating and bigger cable.
Also to be taken into consideration is the distance of the appliance from the electrical source. The greater the distance, the greater the resistance and the less current that will be available at the other end.
Cables must be placed in a situation where they will not be overheated. If cables are run in a loft they must not be placed under insulation and if they are run in insulated walls they will carry a different rating. Please check the tables below and if you are unsure please seek the advice of a professional. Please also note that a lot of electrical work is now covered by the building regulations and requires an installer with the appropriate qualification. Please see our project on Part P.
The type of device which is protecting the point the cable serves is also taken into consideration. These devices are fuses, mcbs, rcds etc and are covered in another of our electrical projects,
The tables below show two different cable and amp ratings. The first table is for cables installed by what is known as Method 4. This is cables enclosed in an insulated wall. The second table is for cables fixed using method 1. This is called clipped direct.
Table 1: Cables enclosed in an insulated wall: Method 1
Cable size |
Rating in Amps |
1mm |
11 |
1.5mm |
14 |
2.5mm |
18.5 |
4.00mm |
25 |
6.00mm |
32 |
10.00mm |
43 |
Table 2: Cables which are clipped direct: Method 2
Cable size |
Rating in Amps |
1mm |
15 |
1.5mm |
19.5 |
2.5mm |
27 |
4mm |
36 |
6mm |
46 |
10mm |
63 |
All project content written and produced by Mike Edwards
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