How are cable sizes selected?

Cable size selection is based on three main factors:

The current carrying rating is determined by the conductor size and the thermal heating of the cable. The cable spacing, application and insulation materials are relevant to the dissipation of this heat.

Voltage regulation is not usually a problem with well-designed electrical power systems but the voltage drop incurred with excessively long cable runs needs to be accounted for.

Guidance on cable size selection for various temperature ratings and wiring methods, along with guidance on voltage drop calculations, are contained in the National Wiring regulations (for the UK, that's BS7671 18th Edition).

Short circuit ratings are based on the maximum current withstand capability of the cable in a short circuit condition. The cable should be capable of withstanding this current without thermal damage until the fault condition can be switched to safety through a device like a circuit breaker of fuse.

For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. Alternatively, assistance in determining the correct cable size for your application can be sought from our experts in The Cable Lab by contacting the technical hotline.

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