How to perform Cable Calculations according to the 17th Edition

If you are just looking for a typical summary of UK Cable Configurations:

Try these...

Domestic Lighting Circuits (Radial Layout) = 1.5mm Twin & Earth Cable (6 Amp MCB Fusing)

Domestic Standard Power Circuit (Radial) = 2.5mm Twin & Earth Cable (20 Amp MCB Fusing)

Domestic Ring Circuit (Traditional UK type) = 2.5mm x 2 Twin & Earth (32 Amp MCB Fusing)

Domestic High Power Radial Circuit (Eg Heating) = 4.0mm Twin & Earth Cable (32 Amp MCB Fusing)

However, if you want to be an electrician and you have a copy of the IET 17th Edition Wiring Regulations close to hand, try these instead...

How to perform UK Cable Calculations using the IEE 17th Edition BS7671 Wiring Regulations

1 - What is the "Design Current"?

You need to work out what the design current of the circuit is. As the "designer" and installer of the new circuit you are responsible for deciding how much power this cable is goingto have running through it.

That's not so hard to answer...

Basically, just look at the labels of any electrical equipment you plan to plug into it and add them up. Think about whether you will be using everything at the same time. Are you, for example, going to be boiling the kettle while running the hoover and watching the telly?

Unlikely, so just make a ball park figure for the maximum consumption of the circuit. For my example, I've decided on 13 amps.

2 - What "fusing" are you going to use?

Modern homes generally use MCB's to protect their circuits (Miniature or Residual Current Circuit Breakers)

*These examples assume that the Fusing will provide overload & fault

current.