20A Radial using 2.5mm

[conny]

I'm not at home at the minute, (getting soaked in a forest and brain has gone numb), but friend called just before to say he wants to add 2 more double sockets to his shed.
He has a single radial circuit with one double socket on it protected by a 20A MCB in one of those garage style CU's Can he add 2 more doubles using 2.5mm or does he need to go up to 4.0mm?
Alternatively can he add the 2 extra sockets and then form a ring back to the 20A MCB?
I'm stuck with my head under a hot tub at the moment and can't think straight about others problems.
Thanks.

 

[EFLImpudence]

Can he add 2 more doubles using 2.5mm or does he need to go up to 4.0mm?

Yes. 4mm² not necessary as circuit limited to 20A.

Alternatively can he add the 2 extra sockets and then form a ring back to the 20A MCB?

No point having a ring for 20A circuit.

 

[conny]

That should make him happy.
Thanks EFLI

 

[AndyPRK]

Can’t see any need for 4mm on a 20A radial

 

[JohnW2]

Can’t see any need for 4mm on a 20A radial

Only if it is deeply buried in thermal insulation etc. (e.g. Methods A, 101 & 103), in which case the CCC of 2.5mm² would be less than 20A (or if there were other major 'de-rating factors at work).

Kind Regards, John

 

[conny]

Spoke to my friend last night. He has changed it to a ring anyway and left the 20A MCB in place.
I asked him was in in the 'fuseboard' back in the house and he said the shed was fed via 10mm swa from a socket in the lounge which is on a 32A MCB ring.
Is this acceptable?
(The CU in the garage has a 30Ma RCD as the main switch and another 6A MCB for his lights. 3 small fluorescents and a slimline led fitting).

 

[JohnW2]

Spoke to my friend last night. He has changed it to a ring anyway and left the 20A MCB in place.

As had been suggested, and with respect, that is just plain stupid and achieves nothing (other than wasting some cable).

Kind Regards, John

 

[conny]

As had been suggested, and with respect, that is just plain stupid and achieves nothing (other than wasting some cable).

Kind Regards, John

I did say that he didn't need to form a ring but he decided to do it anyway.
What I find odd about it all is his Dad, (now retired), used to be a sparky who only ever did domestic work. I've never met his Dad so don't know how good he was or even if he has still got all his mables to be honest so maybe he just wanted to be safe/make sure.

Thanks John.

 

[JohnW2]

I did say that he didn't need to form a ring but he decided to do it anyway. What I find odd about it all is his Dad, (now retired), used to be a sparky who only ever did domestic work. I've never met his Dad so don't know how good he was or even if he has still got all his mables to be honest so maybe he just wanted to be safe/make sure. Thanks John.

Fair enough. There's no problem with doing what he's done, it's just that it was totally unnecessary. These days, the benefits (if any) of having ring circuits (with 32A MCBs) is pretty marginal at the best of times, but with a 20A MCB there really is no point at all.

Kind Regards, John