# Neutral Earth Fault ??

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#### Gazzza

Just started some testing with the multimeter, at one of the switches/ceiling roses that displays the apparent voltage using the neon tester when the switch is on.

So, at the ceiling rose, with bulb in or out, and the switch on or off, the meter readings are :
N-E is always 0 V
P-E is 237 V
P-N is 237 V

Then, also at the rose, switched live to earth reads 237V when the switch is on, 0 when the switch is off.
Switched live to N reads 237 V when the switch is on and reads 0 when it’s off.

I say 237, if I repeat the tests 5-10 mins later it might be 238, it might be 237. I’ve picked up readings as high as 239 and low as 236.
However at any one moment of doing the tests, flicking the switch does not show any differences in the readings between P-E and P-N. And N-E is always 0 V.
(as P-E and P-N always gives me the same reading this suggests to me its fluctuations in the main supply ? Is that normal ? )

At the switch for that light, everything is as you might expect:
With the switch off:
P-E is 237 V
P-switched live is 237 V
Switched live–E is 0

With the switch flicked on the switched live becomes live, and therefore Switched Live to Earth reads 237 V.

In other words flicking the switch on has no effect on the meter reading. Live to Earth gives 237 V. Turn on. Live to Earth still gives 237V, as does the switched live to earth when on.

That to my (simple) mind seems correct. Does that look ok ? (or am I oversimplyfing)

In terms of resistance I wasn’t entirely sure what I was supposed to be measuring. With the MCB off for that circuit and the bulb out at that rose, N-E at the ceiling rose reads 1.4 ohms. P-N and P-E does give me any reading.
(the meter stays on 1 which is its default display in resistance mode).

G

#### JohnD

You were originally worried by the glowing neon on your earth terminals suggesting that earth was live.

Your test meter is showing that your neon tester was wrong. Any leakage is below the sensitivity of your meter. All your other results are as I would have expected and, as a householder doing the non-notifiable work permitted, you seem to have done what can reasonably be expected (n.b. I am not up-to-date with the current set of tests so there may be other points someone will spot)

Into the bin with the neon!

G

#### Gazzza

That's great, thanks very much for all your help.

Neon tester ceremoniously binned.

Cheers

Gazzza said:
Neon tester ceremoniously binned.
Cheers

Shame... I think they are a rather nice curiosity... next time you have chance, in a loft sat on a chipboard floor, use your neon screwdriver on something and try and pinpoint the path to ground that allows the screwdriver to work, for added effect stand or crouch, so the only contact with the floor is rubber soled shoes

#### plugwash

and bloody usefull when trying to fault find christmas lights too.

#### PompeySparks

plugwash said:
and b****y usefull when trying to fault find christmas lights too.

A glowing 'Voltstick' is great for this!

#### cozycats

P-switched live 237v? That would happen with a lamp in, have you tried without a lamp? If you still get a voltage you must have a p-e fault

#### Spark123

cozycats said:
P-switched live 237v? That would happen with a lamp in, have you tried without a lamp? If you still get a voltage you must have a p-e fault

I don't quite understand where you are coming from. You'd expect 237v across L-SwL with an open switch and a lamp installed. With the lamp removed (in theory) the SwL will float, so you should not register any voltage, however in reality there is a whole manner of things such as capacitive coupling to consider and it is anyones guess to what voltage a high impedance digital multimeter (DMM) will register.

G

#### Gazzza

Yes those readings at the switch end was bulb in.

With bulb out Live to Switched live is indeed 0.

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