radial from ring main

[jaresquire]

"unfused spurs should only have 1 single socket running from them .ref 17 edition "


Not as simples as that, there are other circuit configs apart from ring finals eg radials where you can spur off multiple sockets. The standard ring in Appendix 15 is a guide that saves some head scratching as long as you stick to all the restrictions.

 

[nick611]

no thats unfused spurs in 2.5 not 4mm,this adition is not coverd in regs.so how can you know its not allowed?

 

[nick611]

IT IS NOT ALLOWED IN ACCORDANCE WITH BS7671!!!

END OF!!

It worries me when people come out with excuses as to why it wouldn't be a problem. Irrespective of how safe people think it is, what current might flow, what the load is etc etc. It is not an allowable method.

What else would people do in their own judgement of what is safe?

its not considerd in 7671 so how can you say its not allowed?quote me a reg that forbids it

 

[JulianC]

I think the only thing you'll find on this is in the on-site guide, 8.2.4 - "In an A1 ring final circuit.....a non-fused spur should feed only one single or one twin socket outlet"

However, given that the point of the fuse in a fused spur is to protect the cable in the spur, and, subject to installation conditions, 4mm can handle more than 32A and will therefore be protected by the 32A breaker protecting the ring, I am struggling to find a problem with what you are suggesting nick611. As you say, it is not considered in BS7671.

Mind you, I have been at the port.....

 

[Risteard]

I am struggling to find a problem with what you are suggesting nick611. As you say, it is not considered in BS7671.

It is not permitted because it would adversely affect the balancing of the ring.

 

[JulianC]

Aah, the mystical dark art of ring balancing. Not convinced. Where does it say it's not permitted? (playing devil's advocate)

 

[kmcgold]

u can spur off has many sockets has you like if you have fused it down to 13amps and the zs value of the circuit are ok
if no fuse then only one socket etc even if you used 6mm still only one socket etc

 

[kmcgold]

(risteard said It is not permitted because it would adversely affect the balancing of the ring.)

correct.

 

[jaresquire]

Not convinced of this ring balancing either, as we are talking of the same load at the same point of the ring, just different wiring method downstream.
Why am I defending something I've never done though?

 

[JulianC]

Just 'cos we've never done it, nor considered doing it, doesn't mean it's not right! Rather than blindly reading and (mis)interpreting the regs. it's good to think about these things sometimes.

It's clear that this is not covered specifically in the regs. One the plus side, there are no current carrying capacity problems using 4mm. On the down side there's wonky ring syndrome. Now correct me if I am wrong, but I could fit 4 fused spurs off 4 adjacent sockets quite happily and 'correctly' and unbalance me ring.

 

[nick611]

(risteard said It is not permitted because it would adversely affect the balancing of the ring.)

correct.

if the radial came off the center of the ring then it would not.so your answer dosent stand up. does it

 

[j.mawer]

Unless someone extended the ring in the future when it would no longer be in the center.

 

[Guest123]

Truly astonished by this thread.

 

[Octopus]

time to unsubscribe!

 

[kmcgold]

(nick611 said if the radial came off the center of the ring then it would not.so your answer dosent stand up. does it)

??

this is a forum for electricians ?

 

[nick611]

Well 34 posts and still no real reason why this is not allowed.A few random stabs at the regs none of which held water,and a few quite confused by the whole thing.Next week we shall discuss a 4mm ringmain on a 40a mcb. oh hold on hav,nt seen that in the regs book.

 

[kmcgold]

p362 of regs show a ring circuit which has been design for use with 2.5mm cable.
increase to 4mm to allow for voltage drop , etc but do your cals.(all 4mm cable).
you should not spur a radial of an existing ringmain in 4mm

 

[Adam W]

Truly astonished by this thread.

I agree - 4 pages of discussion over whether or not you can just invent your own kind of 'composite' final circuit just because appx 15 of BS7671 doesn't expressly forbid you from doing so.

I mean, seriously, is this a wind up?

 

[Paul.M]

I disagree with the above(kmcgold). At the design stage of this extended circuit we have to consider a few things. What is the flc of the 4 spur sockets? What load is on the existing ring? If a spur is taken from the ring how will it affect it?

By what info that has been posted I can't see a reg to prevent him from doing it, is it best practice is another question. I personally would fit a fcu rated for the 2.5mm cable supplying the radial regardless of what size cable the radial is in. This way if the spur is coming from the first socket of the ring and most of the current is being fed by the shortest section of 2.5mm the spur would not overload that part of the ring. The usage of 4mm for the radial seems excessive if its just for bedroom appliances and you could downsize this.

Do your potential flc calc for the radial, fit a fcu, make sure you don't overload the ring, explain your new extention on the minor works cert and maybe a diagram showing this circuit so no confusion for the next spark. Job done, but not the way I'd do it.

 

[Paul.M]

Double post.