How to find a broken ring!

[philthefish]

Hi all,

I'm new to the forum and am after some assistance please.

At the moment my ring main is being fed by one leg only. This became apparent when I was disconnecting the immersion heater for a combi boiler job. There were two wires feeding out from the Immersion fuse and only one wire from the ring main fuse!

I identified which of the two wires was actually feeding the immersion and disconnected the other one. It is a 2.5mm so I presumed it was the other leg of the ring main. However, there was no continuity between the two live wires. I now guess that the ring is broken somewhere?

ALL of my sockets work, so my next assumption is that the ring is disconnected at the last socket back to the consumer unit?

Can anyone give any fault finding tips please? I have a multimeter and megger available for testing.

Thanks
Phil

 

[EdwardCurrent]

Hello PTF.
Are you sure that you do not have a 'radial' circuits ? What size is the mcb on your power circuit ?

Ed

 

[stem]

First of all the immersion shouldn't be connected to the ring anyway. It should have a dedicated circuit from the CU. However as you are removing it, that may not be an issue now.

Your immersion may be a a spur from the ring, & the second cable may go off to another spur which is not correct. People sometimes do this to feed a socket or light in the loft, or power a shower pump.

Checking the continunity of the ring is fairly easy if you are competant and can do it safely. Don't try it if you're not sure. If it is a ring, at the CU there will be two live wires in the MCB (or fuse) terminal, after turning off the CU remove the two live wires separate them and check them for continunity. Repeat the same excercise for the two neutrals.

Report back on here what you find and someone will advise the next step

 

[JohnD]

you can easily start by finding out which sockets are fed from which fuse. Just take out one fuse at a time and see what stops working.

You say you presume it is a ring, but maybe it isn't.

 

[philthefish]

Ok,

bit more background. When I first opened the fuse box the first 30A fuse was marked up as 'sockets' with 2 wires out of top. The 15A immersion fuse had 1 wire out. It all makes sense so far!

However, when pulling the fuses one at a time to isolate the sockets it became apparent that the sockets were being fed from the 15A!!! Yes, I know

I identified one of the wires from the 30A fuse as feeding the immersion. This is now disconnected.

The wire from the 15A fuse which was feeding the sockets was moved to the 30A.

The remaining wire which was in the 30A originally is the one I'm trying to trace. I suspect some idiot has worked in the box in the past and messed up somehow. There's nothing else in the house that would have a 2.5mm cable other than the other leg of the ring main.

I don't believe it's a radial as it's a 4 bed house and the remaining wire is a mystery. Ideally, there would be a diagram detailing where all the wiring runs and the fault finding would be nice and easy!

I've checked for continuity between the two lives (one that definitely feeds the sockets and the mystery one) and there isn't any.

 

[EdwardCurrent]

Hello PTF.

Maybe its time for you to safely isolate these circuits, and use your multimeter to test each link, from the C/U.
That way you will know exactly what is what and can work out what needs doing.

Good Luck

Ed

 

[sparkybird]

Did you do continity test between N and CPC's of the two legs? What were your results?

Assuming you have a broken ring, here's how I would do it.

Take both 'legs' out of the board - let's call one A and the other B

Connect together L/CPC of A at the fuseboard. test L/CPC continuity at each socket. Readings will rise as you move away from the fuseboard until you get 'open circuit'

Disconnect A L/CPC and connect B L/CPC. Again test at each socket and note at which point you get the open circuit. Between this point and the open circuit on A will be your break. It could be either in one of the two sockets (most likely) or a break in the cable between them

You should not get any one socket giving you a reading on both A and B.
Hope this makes sense

SB

 

[JohnD]

sparkybird, I may be missing something, but why do you say L/CPC rather than L/N? because there are often parallel earth paths especially from supplementary bonding and unintentionally at watery appliances and boilers?

 

[philthefish]

Thanks Sparky,

Not sure what CPC is though? Are you talking about connecting the L&N of each cable (obviously while disconnected!)?

 

[sparkybird]

Hi John
I would use L/CPC (don't forget both are out of the board) as less likely to get odd readings (although hear what you say, but presumably the readings will be very high..). If you use L/N and appliances are plugged in, then you may well get continuity due to the loads.

Also if you find that you've not got a ring,but two radials, then r1+r2 tests are completed!

But I stand to be corrected!

OP - CPC is the electrical term for the earth. (circuit protective conductor), sorry to use 'jargon'. Let us know how you get on with your testing...

SB