New copper light fitting to old wiring (no earth)

[thomp1983]

As Keith said but instead of a long piece of wire you can just use an extension lead if you've got a decent sized one, obviously check earth between the extension and the socket your using first before any other testing

 

[bernardgreen]

Put multimeter in resistance mode (or forward diode test with the beep) and check the reading.

Before testing for continuity do a voltage check (250 Volt AC range ). Any reading above 10 Volts would suggest the Earth is not connected.

This way you reduce the risk of putting 230 Volts onto the Ohms range of the meter and damaging the meter.

 

[thomp1983]

Double post of my message above

 

[Harry Bloomfield]

So to recap you are grounding one lead on the plug socket mounting screw or top pin, you are then using the other lead to check the ground on the ligh fittings and switches.

I'd check all ceiling rose earths and all switch front screws (proves the back box is earthed).

You'll need a long length of wire. 2 people is easier as one can hold on the socket face screw and one on the ladder.

Turn light circuit off first mind!.

Just to qualify that test - It will only confirm if you have some sort of earth at the light, it will not confirm how good it is or whether it is up to an acceptable standard. An Earth Loop Tester is needed to do it properly.

 

[ericmark]

I am afraid we are all guilty of on occasions failing to test, we know we should, and I remember with some water damage the electrician sent by insurance company did test, although he did not record the results.

But where everything seems to be done correctly, I am sure many assume that earth wire is connected to earth, until some one gets a tingle, and I remember trying to trace a loss of earth connections in a house on the Falklands and in the end came to the conclusion there was some junction in the loft and no access to the loft.

So it is down to risk assessment. Or are you willing to take a chance that the earth is connected?

Basic to methods, one is with a low ohm meter, the idea is at least 200 mA is run through the earth wire, and in real terms a 12 volt battery and a head light bulb will show if the earth is good enough to trip an RCD, the earth could be 100Ω and the RCD would still trip, but with a B6 MCB the B means 5 times for the magnetic bit, so 5 x 6 = 30 amp, ohms law 230/30 = 7.6Ω add 5% for safety so 7.28Ω and the question is how would you measure that?

It can be done, but not easy.

 

[plugwash]

Personally I think not testing the earth at all because you can't do an ideal test is a severe case of letting the perfect be the enemy of the good.

 

[markyd1]

How do I test it is connected back to CU?

Get somebody who knows what they are doing

 

[Keithmac]

Of you've got continuity between the lighting and socket earths how slim is the possibly they aren't connected at the Consumer Unit, absolutely miniscule I'd say.

 

[Harry Bloomfield]

Of you've got continuity between the lighting and socket earths how slim is the possibly they aren't connected at the Consumer Unit, absolutely miniscule I'd say.

There is a reason why an Earth Loop Tester was invented, to ensure the connections are sound.

 

[Colin Brenton]

You could combine the method above with a voltage reading at the socket between live and earth...

 

[securespark]

There is a reason why an Earth Loop Tester was invented, to ensure the connections are sound.

But in the absence of that tester, the tests described here will at least confirm a connection which is more than a lot of DIYers do.