Fault Finding On A Ring Main Circuit

[LECIT]

Hi, can anybody give me some advice please. While testing a ring main, I have found that I have an incomplete circuit on the phase conductor, neutral is fine and cpc is fine although the reading on the cpc is quite high.

I have tested each 'half' of the phase conductor by connecting one end of the ring at a time at the consumer unit, and have established which socket outlets work on each 'half', but don't really know what to do next as I don't know which way the circuit is running.

Also, I've removed a few of the socket outlets to try to see if a cable has come loose or anything but the cables are so tight and short that it's virtually impossible to disconnect / reconnect them.

Any halp greatly appreciated.

Many thanks.

 

[oharaf]

Hi LECIT, what reading s do you have? Are they continuity readings?

 

[oharaf]

Hi LECIT, have got to go out now so here is a test/ fault find process to follow.

1. Unplug anything on the ring final you are testing.

2. At the CU (power off) remove both ends of the phase from the MCB,
both neutrals from the neutral bar and both earths from the earth bar.

3. With your meter on a LOW ohms scale, test end to end of the phase

This should be a low reading!

Repeat this for neutral This should be a low reading!

Repeat this for cpc

This should be a low reading! but probably slightly higher than phase &
neutral (which should both be about the same)


Post your readings and we will help further

 

[davelx]

err - I suspect he has already done that and has found that the phase conductor does not have end-end continuity.

He has also identified that the fault lies between two sockets, by powering one side of the ring at a time.

So the problem is between the socket that is live (when one side only is connected) and the next one on the ring. But which is the next? By livening each side seperately, you should know which sockets lie at each end of the faulty section.

First thing now is to check connections at those sockets (with the circuit isolated, of course). Don't just check for tightness, check that the screws are actually tightened onto the copper and not onto the insulation! Give each core a tug - one may have broken but still appear to be in place.

Next thing is to inspect the cable run between them to see if you can identify where the damage might be and fix it if appropriate or replace the cable.

Either way you are going to have to remove and replace sockets. It you replace a cable run, give yourself enough slack to connect up and a bit more just in case.

 

[LECIT]

Hi all, thanks for your replies on this. As davelx states, I have done all of the initial tests and during the continuity tests, I have found the problem with the phase conductor. So I'm pretty certain there is either a loose / broken connection at one of the sockets or a break in the cable somewhere (under the floor, in the wall etc). I know which sockets work / don't work on each half of the ring, but without pulling floor boards up etc I don't know which way the ring is running and therefore don't know which is the last working socket on each half, although logically I could probably have a stab at guessing.

The other problem on this particular job is that there are a few very strange sockets in place that I have never seen before - they are double sockets with sort of rocker switches rather than normal type flick on/off switches and there are no screws holding the sockets in place although they appear to be tight to the wall - I'm wondering if they are those things that you can buy to plug into an existing single socket to turn a single into a double?

Cheers

 

[oharaf]

Sorry LECIT, didn't read properly, post pics of those rocker sockets for us.

Do you have a 'socket & see' device (martindale test plug) you could use this to identify which sockets are not working.

If not you will have to try linking phase & cpc from socket to socket until you find the buggered wire

 

[sparkyspike]

Connect an audible continuity tester between each phase conductor at the CU. (Sorry, line conductor.) Then take a long flying lead. Connect this between two sockets, between where you expect there to be a break. Use a socket testing adaptor or modified plug to avoid taking off all the sockets. The tester will beep between two sockets indicating the fault. Once you've done this, use telepathy to find out exactly where the break is. Probably behind a nail. Or pulled out of one of the two sockets.

 

[AMEdinburgh]

(From a DIYer not a spark). I had exactly what you describe in a "new" ring that had been put in by a kitchen company in a new kitchen installation in a former bedroom in a bungalow I bought. I was testing each conductor before replacing the consumer unit (12 years ago and checked and tested and signed off by B Control as part of an extension elsewhere on the house before being shot down in flames)

In the end, the reason was that they had added to part of the original bedroom ring and decided one of the original sockets was in an inappropriate place and they simply removed the socket and used a bit of 30A connector to join the wires, wrapped it with insulating tape and papered over it with thick scrubable paper so it wasn't noticed. However once I was under the floor, I could see the wires rising up through the floor but nothing above until I started tapping on the wall and discovered it. Live wire was snapped at the screw in the connector. Pulled them back under the floor and put in a junction box - hence my post elsewhere about accessible junctions. At the time was deemed to be an appropriate solution.

 

[plugwash]

At the end of the day if someone really makes the effort to hide thier bodges thier isn't much building control can do about it.

 

[ColJack]

to locate the last socket on a broken ring.

connect the phase and earth together at the board for the half you are trying to find..
then read the resistance at each socket between earth and phase, on the half you are trying to find..

the socket with the highest reading is the one at the end...

we've had to do this on one site in the show flat..
all the electrics were done and tested, then they get an idiot to put up the towel rail..
he managed to put a screw through the cable feeding the fused spur on the oposite side of the wall ( stud partition )..
we ended up splitting the ring into 2 20A radials to get the show flat up and running, on the understanding that it was to be fixed before the place was finally sold..
we couldn't replace the cable there and then since it entailed ripping the ceiling down ( concrete floors above ) and the flat had to be open that weekend..