4mm spured of a ringmain.

[KNIPEX]

im having an argument in work with someone over the following.

there is a ringcircuit wired in 2.5mm t+e on 32a mcb they wish to take a spur of it which is all fine, they spur of in 4mm2 t+e to the new socket

they then want to take another spur from this new socket to feed another and so on, so effectivly your taking a spur of a spur which is a big no.

however as this is wired in 4mm they say it will pass and is fine, i disagree though as you are still talking a spur of a spur even if its wired in 2.5, 4mm 6mm etc.

look forward to hearing your views.

 

[monkeyelectric]

im having an argument in work with someone over the following.

there is a ringcircuit wired in 2.5mm t+e on 32a mcb they wish to take a spur of it which is all fine, they spur of in 4mm2 t+e to the new socket

they then want to take another spur from this new socket to feed another and so on, so effectivly your taking a spur of a spur which is a big no.

however as this is wired in 4mm they say it will pass and is fine, i disagree though as you are still talking a spur of a spur even if its wired in 2.5, 4mm 6mm etc.

look forward to hearing your views.

Yep only one spur per socket or as many as you like off a fused spur

 

[Mark.W]

With him using a 4mm cable sounds like he intends on fusing down to 20A...? Which is then OK!

 

[KNIPEX]

no mate its still a normal ringmain, just the extra sockets, have been spured off using 4mm. as he thought this was ok.

he knows that 2.5 isnt allowed to be spured of a spur thats why he used 4mm

 

[roukel01]

I'm assuming that its a 32amp 2.5 ring, and that their argument is that you can have a 4.0 32amp radial, and so, spuring from a 2.5mm ring with 4.0 should be ok as the 4.0 will carry the load.

Check the back of the latest 17th edition regs, there is a specific appendix showing what you can and can't do to a ring circuit, and as posted above, you can't have more than one spur unless its fused down to 13 amps, this is not because the cable can't handle the load, its because a ring final circuit is designed to have the total load balanced throughout the entire circuit, and not concentrated in one area, by fusing it down to 13amps, you are making sure that the ring circuit doesn't become overloaded in one particular spot.

I hope this makes sense.

 

[Guest123]

Hi.

It wouldn't matter if you spurred off in 16mm T+E as you would be overloading the leg of the ring that the current returns down, think of it as a 32A 2.5mm radial to the socket that your're spurring off plus the additonal spurred sockets.

Our survey said.........err err!!!!!

 

[WayneL]

Hi,

This is a really good question - Just to throw a spanner in the works:-

If you spurred straight out of the Ring Final 32A MCB, then you wouldn't be overloading any part of the ring and your 4mm is protected by the 32A breaker.

Not saying it's right - just causing trouble lol

Wayne

 

[roukel01]

Hi,

This is a really good question - Just to throw a spanner in the works:-

If you spurred straight out of the Ring Final 32A MCB, then you wouldn't be overloading any part of the ring and your 4mm is protected by the 32A breaker.

Not saying it's right - just causing trouble lol

Wayne

That is a very good point, however, you would then be creating two seperate circuits and if you had access to the CU, you'd put another MCB in

 

[Risteard]

you would then be creating two seperate circuits

It would still be one circuit. Look up the definition of a circuit in BS7671.

 

[Guest123]

Surely if you'd gone to the trouble of running back to the CU, then you'd wack it on it's own circuit???.

Back at you Wayne.

 

[WayneL]

Unless...there were no spare ways left so you needed to spur off the ring

I must say it's got me going, this one.

I've been in my big red book for the past half hour and can't find anything definite against it

Anyone else know of a definite regulation or part of the regs that would apply??

 

[Des 56]

Surely if you'd gone to the trouble of running back to the CU, then you'd wack it on it's own circuit???.

Back at you Wayne.

Damn no spare way

A ring main piggy backed onto an existing ring would be one of the reasons why a cross connecting continuity test is carried out,so I cant see this unconventional arrangement getting much support

Zs may also play a part as the new radial wanders off into the distance + the shared current through the legs that as been mentioned

I vote no

Just been beaten by waynes answer

 

[Mr Mark Sparks]

why would you not break the ring at the socket in question
join one leg through
wire the new points
and back to the same socket

i know this is only a hyperthetical question

 

[KNIPEX]

hey who hijacked my post :lol: only joking, this is all good for a debate.

seems i was right then, i need nice hard evidence to go at him though as he is quite high up so any help would be great

 

[nrbspark]

Hi

Just show him appendix 15 and ask him to find if his 4mm spur from spur is apparent.