Socket with earth fault

[MuddyFork]

I've recently bought a house, and when I checked an under-the-worktop washing machine socket in the kitchen, the socket tester said there was an earth fault. When checked with a multi-meter, I can't measure a voltage between earth and either live or neutral at the socket, so presumably the earth is simply disconnected. The live and neutral are OK at the socket, because appliances work when plugged in.

The socket is fed by a double pole switch on the other side of the kitchen, so I guess the concealed cable in between is damaged. The earth at the switch is OK. I've tried a cable detector

, but there seems to be a lot of other metal in the wall (perhaps foil-backed plasterboard), so I haven't been able to trace the cable yet.

My next step is to start cutting holes in the plasterboard and removing wall tiles in an attempt to find the cable fault.

Is there anything less destructive I could try?

[Harry Bloomfield]

Might it not be easier/simpler to find an earth at another socket on the same circuit and loop it across, rather than attempting to find the break?

A broken earth in the cable is the least likely. Most likely are breaks near the ends. Try tugging the earth wire at its ends.

[Jim K]

daft question but it's not clear:- you have had the socket off and checked the earth wire is connected haven't you? if not do so and (safely) test the continuity of the earth wire from the switch to the socket? then you;ll *know* you have a cable fault or not...??

Jim K

[Dave Plowman (News)]

Disconnect the cable and check the ECC with your meter first? Never assume a fault *must* be in the most awkward place.

If your test meter leads won't reach connect the ECC to say the neutral at one end and measure between them at the other. After disconnecting, obviously.

[Dave Liquorice]

Continuity of the earth between the cable end in the switch and same cable end in the socket back boxes? If the earth is broken and it not obvious when you waggle the cable ends I'd be a bit concerned that there is a nail or something slap down the center of the cable.

While you are at it check that the DP switch you think is controlling both legs of the cable really is controlling both legs not just one of them, particularly if there are a number of cables in the same back box (grid switch?)

[Lobster]

You don't say, but at the risk of stating the bleedin' obvious, presumably you've unscrewed the socket faceplate to check whether the earth wire has simply become disconnected from its terminal?

If not (with the power turned off at the mains), I would next try disconnecting all the terminals within both the socket and switch, and check for continuity between the two, of all three wires (do you have a cheapo voltmeter, or a battery/bulb combo?) That would at least definitively diagnose the problem, if it's what you suspect.

What is the cable route betweem socket and switch like?

David

[MuddyFork]

Thanks for the replies. I should have said that I've already removed the socket and the switch from their back-boxes to check for loose connections. The idea of doing a continuity test on the 3 wires with the power switched off is a good one - I will try that. Shortest route between the socket and the switch involves passing behind a sink and several kitchen cabinets, and a layer of wall tiles. Presumably that is the route the electrician took when the house was built 15 years ago.

[Jim K]

to me at least, it seems a bit odd why anyone would want a socket controlled by a distant switch *across* a room? could be the tip of a "homemade" bodge job here....go carefully!

Jim K

[cynic]

You have of course checked continuity from earth terminal to "earth pin" at the socket? a simple faulty socket is not beyond the realms of possibility.

[Peter Parry]

Have you tried measuring continuity between the earth cable (not the screw connector) at the switch and the socket? Cable faults are relatively unusual unless the cable runs in notched beams and someone has nailed a floorboard down and put the nail through the cable.

[Bill]

In message , Harry Bloomfield writes

Would that be a good idea? If the earth is broken then what other damage has happened to the cable?

[Andy Dingley]

I've had those in kitchens where the dishwasher, fridge and washing machine are semi-permanently wired, and the control switches have been bundled to one place.

[Jim K]

interesting... would that be allowed under todays regs? isn;t there some mention of "local" control of appliances presumably so it's intuitive how you turn the smoking washer/etc off in a hurry for e.g.

Jim K

[js.b1]

Within 2m of the appliance, which in a small kitchen may be on the opposite wall.

Some people like a single isolator for all the sockets in a kitchen on safety grounds, and others with very small fingers use grid switches.

[John Rumm]

Sounds possible...

First thing you need to do is a visual inspection - have a peek behind the switch and the socket and look for loose wires.

Why not check to see if the cable is actually at fault before you start wrecking the kitchen?

Assuming the visual check looks ok, disconnect the cable (having turned off the power obviously) at both the switch and the socket. Short all three conductors together at one end, and then measure resistance between them at the other. Only if you then have an open circuit do you know there is a genuine cable problem (assuming you are *sure* the cable only goes from the switch to the socket and nowhere else).

[MuddyFork]

Thanks for all the replies. I have now disconnected the cable at both ends, and measured the resistance of each of the 3 conductors. The live and neutral are fine, but the earth is open circuit. I've tried tugging on the earth wires at both ends, and both seem undamaged, so it seems to me that the earth conductor is broken somewhere in the middle, even though that seems unlikely.

[Dave Plowman (News)]

I'd look along the likely run for any fixing etc that may have pierced it.

[js.b1]

Heh-heh, could this be a kitchen fitter with a hidden jn-box somewhere with overheated terminals or plaster splodged into a taped up chocolate block connector?

[ARWadsworth]

Unfortunatley it is quite common. People drill through cables breaking the CPC.

Have you got any other under worktop sockets that you could take a spur from and save you the effort of replacing the damaged cable?

[Lobster]

Seems the most plausible cause... either that, or as someone else has alluded to, there could be a poorly wired join of two lengths of cable.

Either way, I wouldn't be trusting that the L & N wires are 100% OK - there could be a short circuit waiting to happen. I think you need to trace the positiom of the fault, ot isolate the length of damaged cable and run a new length in its place.

David