Extending ring main with 1.5mm cable

[ban-all-sheds]

I know I'm clutching at straws!!!!!

You are.

Firstly I don't see how you could fuse down part of a ring in the way that you describe - if I've read it right you have this:

Secondly, you can't run the whole ring on a 20A breaker - the only ring final permitted by the regulations is one with a 30/32A device and cable with a minimum size of 2.5mm² and a minimum capacity of 20A.

 

[Taylortwocities]

Aye. and a 1.5mm ring from a 20A cb is not a recognised circuit arrangement.

I would hate to do the current calcs and sign that baby off!

 

[ban-all-sheds]

The calculations are in the pre AMD-1 16th, aren't they?

⅔ IIRC, so for a B20 you'd need 13.33A.

 

[Spark123]

I wouldn't bother with attempting to do the calculations, the use of 1.5mm is a fudge and it should be replaced with the proper size cable for the circuit.