Lighting circuit - Earth Problem?

[dan83590]

I may need your help.

We have purchased a new metal light fitting. What I have done so far is this.

I have removed the cover from the existing plastic pendant. There are 3 wires, live, neutral and earth. I have a neon screwdriver. With the switch off or on the neon lights up when on the earth.

I also have a cheap multimeter. With the switch on between live and neutral I get 230v ish AC. Between live - earth I get 120v ish.

I have looked behind some of our other switches and not all of them are earthed. We have some metal switches that are earthed, some are not. I've not put the meter on those but the earthed switches light up the neon.

The new light fitting is not double insulated.

It's an old place and I have no idea who installed the electrics here. It has been re-wired at some point but before we arrived.

I'm not completely green and could fix it with some direction but I am no electrician.

Do we have a major problem here??

 

[electronicsuk]

Sounds as though the earth connection back to the MET is not continuous. This could be a basic problem restricted to the lighting circuit, or it could indicate the lack of an earth connection to the entire installation.

Ideally you should have the entire installation checked over by an electrician, as the latter scenario is immediately dangerous, and a fault with any part of the electrical installation could cause the entire installation to become live. It's not completely unheard of for a DNO fault on a TN-S supply to cause such earth faults.

That said, if you feel confident enough to do so, you could perform the same tests with your multimeter that you have already carried out on the lighting circuit, repeat them on a different circuit, and report back with your results.

 

[dan83590]

All other circuits are fine as far as I know, I have tested those before, the workmanship is poor but electrically okay.

What should I do or test on the lighting to post up?

 

[Hibbo]

Isolate the lighting circuit and check for dead, then check for any voltage at the light fitting between earth and live, and earth and neutral.

If this is OK (no volts) then get a long piece of wire and connect it to your main earth terminal at your consumer unit, then use this 'extension lead' to continuity check the earth terminals at the light fittings and switches back to the MET. It's a good idea to knock off your main isolator before doing this (get the torches out!)

Good luck and stay safe

 

[dan83590]

Thanks I will.

So assuming there is no continuity what should I do then?

 

[dan83590]

Okay...

I have established that there is no earth to the consumer unit on the lighting circuit.

Next problem.

We live in a top floor flat and the CU is three floors down in the basement. Can I take an earth from the sockets? I realise that this is probably not best practice, what else can I do?

 

[ericmark]

The Electrical Safety Council has issued instructions here in PDF format which details what should be done where it is found the lighting is not earthed.

The BS7671:2008 rule book is not so easy going as Electrical Safety Council and one thing it says is where an earth wire is not part of the cable it needs to be at least 4mm. Also it says the earth and the supply cables should follow the same route.

As a result the idea of adding earth cables is not really practicable and only way to correct is often to renew the cables.

On a personal note if it were my house I would first install a RCD on the lighting circuit then bit by bit start the re-wire.

However this would not completely comply with regulations until complete and where one is straying from the regulations then you must do a risk assessment and if I was to do this with my house or my parents house I would consider it to be an acceptable risk. However with my daughters house with two grand children running around likely I would consider the risk was too high.

At the end of the day you have to consider if you want to take chances or if you want it all corrected ASAP. Any Electrician would likely consider it was not worth the risk as in today's climate people are all too quick to take tradesmen to court. In the old days I have seen all sorts of lash ups to correct this sort of problem and to be fair likely they worked. but most domestic electricians have today to be members of an organisation who has the right to inspect their work and to get expelled would mean they could no longer work on many of the jobs found in the domestic market so they will no longer cut corners. Which to be honest has to be good!

 

[ericmark]

Okay...

I have established that there is no earth to the consumer unit on the lighting circuit.

Next problem.

We live in a top floor flat and the CU is three floors down in the basement. Can I take an earth from the sockets? I realise that this is probably not best practice, what else can I do?

What a silly idea one would have expected the CU to be local. As an electrician our hands are tied. But looking at common sense if there is:-

Equipotential bonding. Electrical connection maintaining various exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential. (See also Protective equipotential bonding.)

Then it will remove many of the dangers. However read the PDF document at links and then consider how to proceed.

 

[dan83590]

So really what you are saying is that the lighting circuit could do with a full or partial rewire to meet the latest regs?

 

[ericmark]

Yes but read the link.

 

[dan83590]

Reading through it now matey. Thanks for the link.

 

[sparkwright]

are you certain the lighting cable from the fuse box doesn't have an earth?
sometimes the earth wire gets cut out.
is the cable in a tube or cavity to allow a new one to be pulled through?

 

[Hibbo]

When you say that there's no earth connection to the CU, do you mean that there's no CPC (earth wire) in the cable coming from the CU, or that it's just not connected?
What type of cable is it?
Do you have a 4mm^2 (or bigger) earth cable coming in to your flat for main bonding to water/gas pipes?

Don't worry marra, whilst your installation is extremely unsafe, be glad that you've found this problem, and there will be a way to put it right.

 

[dan83590]

The lighting circuit does have an earth wire inside the cable but it's not connected and in most places it's been cut so short it could not be connected.

I haven't traced exactly where the cables go yet but it would be my guess that they run up 3 floors through an old lath and plaster stud wall, that is only a guess mind you.

I can't say I've spotted any earth on any of the pipes, but I'll have a closer look.

There is an earth block downstairs which is separate to the CU's downstairs (we have 7 flats in total in this house), it looks like each flat has been earthed into this block.

 

[Hibbo]

So the lighting cable from your flat down to the CU has an earth in it, but this conductor has not been connected at the CU and cut so short that it can't be? What kind of idiot would do that? How old is the buidling / wiring?

If there's a main earth terminal in the basement, then at least you should have an main equipotential bonding conductor coming in to your flat somewhere.