No continuity on live ends of ring

[Mike10695]

Hi Im new to fault finding and would appreciate any help I can get, I have been called to a job where there is a open circuit on live end of the ring final, I have checked every socket for loose connections or breaks and they all check out good, the house is a 1960s property, I have no access to floors as they have recently had new flooring throughout the upstairs, im starting to think there are many jbs with in the floor as I can not locate the fault, is there any suggestions you can make to rectify this, cheers

 

[sparkwright]

All sockets you check, make sure they actually are tight and secure, then retest.

Check at the consumer unit that you have the correct wires, and it's not a wire for a different circuit.

If you really can't find it, you need to find out which section of wiring has the break. This can be determined by dividing up the circuit, by disconnecting sockets temporarily.

Check again if there are some sockets you haven't seen. You never know.

If no luck, and you find where the break is, you may have to run a new cable to maintain the ring.

The other alternative, if there's no other option, is to remove the damaged part of the circuit - the live, neutral and earth, and have the circuit as a radial circuit, ie not a ring. This will require a 20 or 25amp fuse, MCB, RCBO.

Or, make it into TWO radial circuits.

 

[sparkwright]

Are there any surface mounted double sockets?

It's not uncommon, in a house of this age, to remove a flush single socket, and fit a surface double socket over it, making a joint within the single back box.

As far as dividing the circuit goes for fault finding, disconnect a socket somewhere near the middle of the ring, then test each 'leg'.

On the faulty leg, disconnect somewhere in the middle of that, test, and so on.

 

[Mike10695]

All sockets have been double checked and restested, ive also done the half method however im worried that there is a jb which has the loose connection or break which I know I csnt access?

 

[AndyPRK]

You can down rate the circuit in that case to a 20A Mcb.

You should be able to have an idea where the fault is. If you separate the lives and either power one end only or use a wonder lead some sockets will work. Others won’t. Where they stop the break will be close.

 

[Mike10695]

I have access to the first leg as the kitchen ceiling is down, I can trace the second to a point and at that point I believe there is a junction box, its very odd each socket upstairs has the ring looping in and out however each socket down stairs has been spurres off directly from the socket above, after investigation and testing, this is why I believe the loose connection is at a jb, I think my only option would be to downgrade the circuit to radials? What is throwing me off is even though the live ends are open, if I put both legs on a 20amp, the neutrals would still be dependant on one another?

 

[sparkwright]

Surely you need to completely disconnect the broken section completely - L, N, E.

You can't really leave the broken section in place even if it is on a 20amp device, as there may be some live open ends somewhere.

Of course, if there is a hidden joint, this may result in a socket or more not working...

 

[Mike10695]

Very true, the issue I have is its a standard house, 3 sockets in the master, 2 in the remaining bedrooms, one on the landing and hall, then one in each room as spurs downstairs, the confusing part is the fact they all work?

 

[sparkwright]

Very true, the issue I have is its a standard house, 3 sockets in the master, 2 in the remaining bedrooms, one on the landing and hall, then one in each room as spurs downstairs, the confusing part is the fact they all work?

They would all work if there's only one break, as they are fed from two directions.

IF there is a junction box, there COULD be one ring and spur wire connected, and the remaining ring wire broken off.

 

[baldykev]

How was this fault discovered ?

 

[AndyPRK]

I guess this could be a normal arrangement. Ring around the upstairs floor and then spur down to each socket on the ground floor.
Save cable and ring length. A pain with JBs though.

You have 2 choices.

1) connect both ring ends to the same 20A MCB. Which was what i was suggesting.
2) correctly split the ring. and use 2 MCB's. But if you could split the ring, you could probably fix the fault!

You could even use a 25A MCB if once is available for your board (as 2.5mm should be rated for 27A)

 

[Mike10695]

Is the 20amp sufficient for the both live ends to be connected? I believe there are 18 sockets on the circuit

 

[AndyPRK]

Probably. Depend what’s plugged in,’ in the kitchen

 

[sparkwright]

Really and truly you need to determine where the damaged section IS before you do anything else.

When you know that, you can decide what the BEST remedy is.

Even working out roughly where the fault is may help you discover a hidden, accessible socket or joint.

A nail through a floorboard into a cable notched into a joist was enough to cleanly break through an earth wire on a 2.5mm2 T+E on a job I did some years ago. Everything else was intact. So I suppose it could happen with the live wire.

So, you can see it is important to repair this socket properly, rather than ONLY change the MCB.

 

[scousespark]

Very true, the issue I have is its a standard house, 3 sockets in the master, 2 in the remaining bedrooms, one on the landing and hall, then one in each room as spurs downstairs, the confusing part is the fact they all work?

if the sockets are all working, what happened to get the owner to call you in?
I’m confused by your quote that splitting the ring gives continuity down both legs. If the full circuit has a break, you should see a break somewhere in the split legs. Try drawing the circuit diagram.