Cable sizes, kilowatts and amp ratings

When you are working with any sort of electrical job in the home, it is vital that you know all about the correct sizes of cables to use for the right job, especially when connecting to the mains.

Any cable must be the right size to cope with the power demands of the device that it is connected to, and this guide can tell you about the different amp ratings and kilowatt levels for different cables to help you choose the right one.

Any household appliance will have a required amp rating, so knowing what cable to use will be one of your first steps. As with any job, however, you should never mess with electricity unless you are 100 per cent sure. If you don’t know what size of cable to use, always ask a professional for help.

Level of difficulty

Level 1: Beginner

What you need


Different cable sizes

Choosing the right cable size for any wiring you are going to be carrying out is absolutely vital. If you use a cable that is of an insufficient size, you could end up with a dangerous situation where it becomes overheated and causes a risk of fire. Always double check amp demands on devices and ensure that you are using the correct size of cable before you wire it.

The smallest cable has a conductor size of 1.0 sq. mm. This cable will have a current rating of 10 amps, and will be able to deal with a capacity up to 2.4 kilowatts. A 1.25 sq. mm cable has a current capacity of 13 amps, and can handle up to 3.12 kilowatts.

The next size up is the 1.5 sq. mm cable, which has a current rating of 15 amps and a capacity of anywhere up to 3.6 kilowatts. The most common type of cable for connecting things like a spur socket or a new cable to a junction box will be the 2.5 sq. mm size. This has a current capacity of 20 amps and the ability to deal with up to 4.8 kilowatts.

The largest cable size you will find will be 4.0 sq. mm, which has a current capacity of 25 amps and the ability to handle anything up to 6 kilowatts of power.

When choosing a cable for wiring a device or appliance, always ensure that you check and double check the required capacity, as using a cable that is too small can have dangerous consequences in the home.

Safety tips

Never chance it with cable sizes. You always need to make sure a cable has the required capacity to deal with electrical flow. Failure to do this can result in a dangerous situation with overheating and a real risk of fires.

As always with electrical jobs, never carry out a task without being 100 per cent sure of what you are doing. If you’re not, call in a professional to complete the job for you.

Please note that all our DIY guides and ‘Expert answers’ advice have been written strictly for reference only. Rated People do not accept any liability for any damage caused to an individual, property or anything else as a result of following our DIY guides and using our ‘Expert answers’ advice.

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