Neutral fault?

[watchdog50]

Hi there. I'm hoping that someone out there will be able to advise me.

Last night I plugged the vacuum cleaner into a double wall socket. A lamp was plugged into the other half. As soon as I switched the vacuum cleaner on, the lamp went out (the vacuum cleaner wouldn't work either). Probably a fuse I thought. However all the other sockets and lights were fine. I used my socket tester which showed that there was a neutral fault. My power detector seemed to back this up and registered a current when I ran it up the wall. Given that all the other sockets and lights were fine, I assumed that the problem must be with the socket itself. However, upon checking the socket, all connections were correct and having used all my other gadgets, I'm satisfied that the socket's fine.

This particular socket did give me some trouble a couple of years ago. Sometimes it would work and sometimes it wouldn't. However, the problem seemed to sort itself out and since then, until now at least, I've not had a problem.

Now I'm not an electrician by trade (obviously) but would like to consider myself a relatively capable DIY enthusiast. Even so, this has me stumped. It was clearly the sudden demand which caused the circuit to 'blow'. However, shouldn't it have been the fuse that went? As I say, I'm not an expert but I wouldn't have thought that a neutral connection somewhere in the circuit (which appears to be the problem) would have 'blown' in the manner that it apparently did.

Any ideas?

 

[PrenticeBoyofDerry]

and this socket is on the same circuit as all the others, you have continutiy of the condutors, the fuse at the boards not blown and the terminals are all tight in the outlet.
Try a new face plate.

 

[watchdog50]

and this socket is on the same circuit as all the others, you have continutiy of the condutors, the fuse at the boards not blown and the terminals are all tight in the outlet.
Try a new face plate.

Yeah, even though I'd checked it and it appeared to be OK, the face plate was the only variable. As such, I did pop out to Focus this morning and bought a new one. Alas, the problem persists.

The only thing I can think of is that there's a problem with the connection at the junction box or a break in the cable between the junction box and the socket (the socket's on a spur). However, the suddenness with which it went and the fact that it occured when another appliance was introduced to the socket leaves me thinking that there must be something more to it than simply a loose connection and it would be extremely unlikely for core & earth cable to break as suddenly.

 

[holmslaw]

..

 

[watchdog50]

OK. This is all very strange. I've now lifted the floorboards upstairs and found the junction box into which this socket (along with one other) goes. Again the connections are absolutely fine, as is the other socket. Therefore, logic suggests that the fault must lie in the length of cable between the junction box and the socket but as I said earlier, this is twin & earth cable and shouldn't break.

 

[Chri5]

Shouldn't and hasn't ..............

You need to do some basic end to end continuity tests.

Have you a multi meter? If so extend one lead with wire to allow the meter to read over the length of each cable (roving lead method).

Alternatively you can join cables together at one end and test for continuity of pairs of cable from one point.

How old is the cable and fittings ?

 

[ericmark]

A guess but I would say likely a spur?
And if so likely the problem is in the socket it is supplied from.

Of course it could be broken ring. And it could also be some hidden connection where someone has extended a cable.

But try for simple first.

 

[bernardgreen]

And it could be a nail through the cable which cut the neutral but then the metal of the nail bridged the gap between the cut ends. So it still "worked" as conductor.

But now the joint cable-nail-cable has deteriorated into a thin connection that was adequate size to carry the small current for the lamp but when the motor in the cleaner started it's inrush current was too much for then thin connection in the cable-nail-cable and this thin connection "blew" like a fuse wire.

 

[Taylortwocities]

If you have one (hidden) junction box you probably have others.
You should not have any unless they are accessible.

You need to take a structured approach to tracing the wire back from the socket until you find where the problem is.

Do not use socket testers or power detectors (or neon screwdriivers) to find this problem. They tell lies and will lead you down endless cul-de-sacs.

You need a proper voltage test instrument or a multimeter as you need to prove live and neutral continuity.

If you aren't sure then get a competent person in.

 

[watchdog50]

Oh, I thought I'd posted the result. Obviously I'm as good with computers as I am with electrics i.e Not very.

Anyway, I decided to go back to basics and disconnected all the wires from the junction box whereupon I found a rather suspect scorch mark under the neutral connections (hence the neutral fault I suppose). Still not sure why it would have happened but I replaced the junction box and now everything's working fine again.

Thanks for all your responses.

 

[Taylortwocities]

Glad you're sorted.
Sounds like there was a bad connection in that junct box. They can loosen up over time - that's why they are supposed to be accessible.

Strangely it seems to be the neutral is more likely to fail.

 

[bernardgreen]

Strangely it seems to be the neutral is more likely to fail.

It was said on the forum recently that installers seem to pay more attention to the more dangerous / important / complicatedly switched and otherwise more interesting Live wires and pay lip service to connecting the boring old neutrals. The live terminals get that extra twist of tightness.