earth fault indicated by martindale tester on ring main

[squowse]

hi. about half the sockets on my downstairs ring main are showing an earth fault using a martindale plug in tester. i think that this means there is no earth at this socket?

this is a potentially dangerous fault i think.

am i right in thinking that there must be two breaks in the earth continuity for a fault to show. with all the sockets in between having the fault. i have some of the wires exposed and it's a bit of a chaotic arrangement, ie hard to see which socket leads to which.

is there any trick of the trade for tracing the fault. i was thinking to attach a 9v battery to the earth and either live or neutral at one of the first sockets and then testing using a multimeter all the way round.

 

[Spark123]

Yes it is dangerous if you do not have a CPC at each of your sockets.
One way to fault find is to disconnect the wires for the ring at the consumer unit. Isolate the CU and make sure it everything is dead. Be carefull as the meter tails will be live with the main switch on. Start by checking end to end resistance of the L, the N and the E. You should have a low resistance between each of the ends.

Take one of the ring cables at the CU and connect the red to the E. Leave all the wires separated at out the other end.
Go around each of the sockets and check the L-E resistance, noting down the resistances.
Disconnect the L-E link and separate them out. On the cable at the CU, connect the L-E two together. Do the L-E at each socket again.
You should see the resistances go up the further away from the CU you get to the point where there is a break and it goes open circuit.

 

[squowse]

thanks for the advice but i am a bit nervous to open the consumer unit as it is not possible to isolate the whole thing without removing the big sealed fuse i think?
i will open all the sockets and i must find the faults eventually. there must be 2 breaks?
if i can't find it i will get my electrican round.

 

[Spark123]

You are right in there will probably be two breaks, however there is also the chance of the L - N being broken too.
If you are not happy with working inside the CU then it will be better to get a sparky to do it.

 

[hairyben]

i will open all the sockets and i must find the faults eventually. there must be 2 breaks?

At a guess, more likely that the sockets in question are on a continuous spur.

Impossible to tell though without investigation.

 

[Taylortwocities]

Hairy, my thoughts exactly. Just because a socket has two cables does not mean that it is part of a ring final circuit!

Possibly someone has added a string of sockets to a ring and the earth has come loose in the process.

Or (as I found the other day) some person has broken the ring while doing some works and didnt reconnect it as a ring.

Firstly you need to do a continuity test on the ring from the consumer unit.
Call in a qualified spark if you are not confident on how to do this.

 

[squowse]

well i located the 2 breaks by working my way round with the tester and drawing a plan. i fixed one -

a terminal strip with three cables into one side and one into the other. ring and 2 spurs. i have replaced it with another terminal strip and put two cables into each side for temporary fix as the junction box i had wouldn't grip 4 cables. will sort it with a couple of decent junction boxes tomorrow.

the other is trapped behind units that are coming out in a week so will get that then. at least all the sockets are earthed now. i realise that my ring may not be a ring due to possible interruptions on the live and neutral as well. but i don;t have more than a kW on the whole ring so ok for temporary. will get the sparky to check everything when he's here in a week or so.

thanks for advice.