Spurring from ring main

[joelypops]

Talking to one of the lads on site today and he asked why i was adding a 13a un switched spur to the radial i had pulled in to the extension. Explained why it was there etc then he said why don't you run the radial in 4mm, doing away with the need for the spur? I have never come accrossthis and never really thought about it. Had a flick through the big green book and couldnt really come up with a solution so thought i would ask here. Can you run a radial spur to several dsso in 4mm or does it need to be 2.5 with a 13a fcu?

Joel.

 

[telectrix]

theoretically, it looks OK< but if your take off point is not close to the mid point of the ring, then you risk overloading 1 leg of that ring.

 

[joelypops]

Ok, so what about this: if i were to split the ring at that point, messure r1 + r2 on each leg to gve a rough idea of each leg. Say they are almost identical readings then it wouldnt go against any regs etc? Only thinking about it now as i got a job next week tonput power into someones garden for electric awning and lights aswel as a few outside sockets. I'm thinking running 4mm is going to be easier than extending both legs of the ring.. getting 4mm into the back of the existing dsso might be a little tricky i suppose..

 

[telectrix]

i'd strongly advise against doing it that way. for one, any faults outside ( damp etc.m) would trip the RFC RCD and whatever other circuits on that RCD. i'd fit a separate RCD/MCB mini CU alongside the house CU and go outside with SWA.

 

[joelypops]

Good point well made.. i am going to look at thr job fridqy so will mention that to them

 

[HappyHippyDad]

Hi Joel,

I thought about this a while ago and asked it on a thread I think. It made sense that I could take a radial off a ring in 4mm! In theory (like Tel says).. yes, but BS7671 makes it very clear that an unfused spur (from a ring) should only feed one socket (single or twin).

 

[joelypops]

Fair enough, think I'll just stick to extending the ring or adding a fcu before the spur. Ta!

 

[piccollo]

Joe, tele has given you best suggestion, but a bit confused with your original question, in as much as originally it was a radial into the extension & then was sockets & an awning & lights. Is this new work adjacent to the property or fixed to property. Are the sockets out side? thus weatherproof type. How were you going to control the lights [ just plug in to sockets or fuse down with switches]. A fuller outline / details would help. There are many on here that would help, especially if you are struggling. piccolo

 

[joelypops]

Hi piccollo, original question came from radial into extension, then i think i confused things a bit when i said about another job which wants power outside for a couple sockets and power to electric awning. Been to look at it since then and there are alrewdy two 5a switched feeds running outside for the lighting. It was omly the power i was wondering about, wether it was worth taking 4mm from the ring, thus keeping a 32A supply outside etc. But its really not worth it. 2 double sockets and an awning which only requires a 3A supply.

Ta!