Breaking a lighting ring circuit in the middle

[mmi2001]

We have a lighting circuit on a dimmer and with 5A round pin sockets for standard lamps and table lamps (ie: no ceiling roses)

After about 7 years of reliable use it started to take our trip out (and the dimmer!) Mostly intermittent but almost instantaneous now.

Fault-finding showed that if one section of the wiring were removed (just the live in fact) it all behaves perfectly.
A Fluke meter is not good enough to see a passive fault on the line - a PAT tester might (but I haven't got one)

Electrically it all works in that condition and all the lamps are low current (LEDs etc...) but the ring is not a ring anymore (although it is on the neutral still)

Is it OK under the regs to leave it like that?

(The cable that looks to be in question is inaccessible without pulling up the floor and there is nowhere else to run a parallel replacement - not a viable option)

 

[Taylortwocities]

It is ok. Better to remove the neutral too and completely isolate the faulty section.
Even better to find out what is causing the problem.

Big note: lighting circuits are not "rings", they are radials - so disconnecting as you have done only affects the sockets & lights downstream of the disconnection.

 

[Mike Johnson]

It sounds like the other side of that connection has been taken back to the CU or it would not still be working on all the 5A sockets, someone installed a lighting ring of 5A sockets, they now have two radials on the same MCB?

 

[telectrix]

It is ok. Better to remove the neutral too and completely isolate the faulty section.
Even better to find out what is causing the problem.

Big note: lighting circuits are not "rings", they are radials - so disconnecting as you have done only affects the sockets & lights downstream of the disconnection.

it could be a ring if it's feeding 5A sockets.

 

[Taylortwocities]

Hmm, needs investigation - methinks.

 

[mmi2001]

It is ok. Better to remove the neutral too and completely isolate the faulty section.
Even better to find out what is causing the problem.

Big note: lighting circuits are not "rings", they are radials - so disconnecting as you have done only affects the sockets & lights downstream of the disconnection.

It sounds like the other side of that connection has been taken back to the CU or it would not still be working on all the 5A sockets, someone installed a lighting ring of 5A sockets, they now have two radials on the same MCB?

Yes I think that's correct. It is wired exactly like a 13A ring would be - ie: from both ends - only using 7 or 8 5A sockets instead. And switched from a single dimmer on the wall. (Remote control was offered I remember but we didn't want that)
I have never installed anything like this myself and only came across this kind of system about 10 years back perhaps. This one was part of a big apartment remodel and with building control etc.. was of course all signed off correctly at the time.

 

[Mike Johnson]

You need to isolate the defunct leg of that ring? perhaps into a couple of Wago connectors, turn off the MCB before work, you may still trip any RCD that may be protecting this particular circuit, IMO leave the earth intact and just isolate the L & N in both sockets.

 

[mmi2001]

You need to isolate the defunct leg of that ring? perhaps into a couple of Wago connectors, turn off the MCB before work, you may still trip any RCD that may be protecting this particular circuit, IMO leave the earth intact and just isolate the L & N in both sockets.

That's pretty much what I've done. And so far it's all looking good.

Just wanted the expert opinions on whether leaving it in that condition was against the spirit of the British Standard - ed18 or wherever it is now!

The duff leg goes across an external threshold, so there maybe something underneath that we can't see, like mice chewing the cable and/or water ingress (if it's been chewed!)
Without major excavation it can't be replaced.

 

[telectrix]

just diss. the N section as well. what rating is the MCB feeding the circuit?

 

[Taylortwocities]

Unusual set up. Surely the sockets “ring” starts and finishes at the switch, not at the consumer unit?
There’s no point to a ring if assuming the MCB for the circuit is 6A.

 

[mmi2001]

Unusual set up. Surely the sockets “ring” starts and finishes at the switch, not at the consumer unit?
There’s no point to a ring if assuming the MCB for the circuit is 6A.

...truth is I don't know. I didn't install it. I suspect as you say it starts at the consumer unit and that the dimmer / switch on the wall is in the live path upstream.
All I can say is that every 5A socket has two twin/Earths going from / coming to it and it can be broken anywhere with the live feed appearing at both ends - but obviously a section can be isolated (as I've done) and there will be 240V on the incoming leg in either direction - exactly as you would get with a 13a ring.

Interestingly though we happen to be doing another renovation project elsewhere with completely different builders/installers and sparks and they are providing the same type of system in two master beds and a living room. And the second fixes have all just been done - so (and I didn't think of this before) I'm going to ask the electrician doing the job how he has connected everything up.

 

[mmi2001]

just diss. the N section as well. what rating is the MCB feeding the circuit?

6 amp

 

[loz2754]

It can't be a ring if the 5a sockets are all controlled by a dimmer on the same circuit.
(Scratches head....)

 

[Dave OCD]

There could be two cables into and two more out of the dimmer, very unorthodox though.

 

[Taylortwocities]

It can't be a ring if the 5a sockets are all controlled by a dimmer on the same circuit.
(Scratches head....)

Exactly, it must be a ring from the dimmer output, not from the CU.