Earth funnies and phantom voltages on lighting circuit

[ericmark]

Does it matter, be it red, yellow, blue or brown, black, grey, in domestic it will need some over sleeving. I found 2 x red or 2 x brown a pain, so want cores identified, be it either system. I note the wires to my thermostat are red, yellow, blue but boiler end brown, black, grey, never have found the junction, and one open circuit, so I use them with 12 volts heat link to thermostat so however joined there will be no problem.

 

[securespark]

All the red/ red or brown/ brown I have worked on has been marked in one of two ways:

1. One core has colour all the way through the insulation, the other only the outer, the inner portion is white.

2. One core has a ridge running down one side of it.

 

[EFLImpudence]

Going back to the question that started all this:

I've been told this 'no earth on the lighting circuit' malarkey was permitted because of trying to save on copper in post-war austerity times.

It is probably more that it (the earth on a lighting circuit) was not necessary.

It is only recently that a regulation was introduced stating that a Circuit Protective Conductor (earth wire) shall be fitted even though not required.

 

[FrodoOne]

I've been helping a friend out with some electrical work and issues. She was complaining about getting a slight 'buzz' from the hall lightswitch (brass finish type).

One must wonder what is meant by "getting a slight 'buzz'"

I tried it and got diddley squat. I drew the line a licking it. However when I put a meter on it to earth I got about 50-60v AC and connecting it to earth I got a current of almost exactly 1 milliamp.

The "meter" may (almost certainly) have been a High-Impedance "Digital meter".

*Theoretically* the circuit is earthed (well its got an earth wire anyway) but I'm pretty sure when I did a continuity test to a known good earth I got 'open circuit'. I fitted a new outside light anyway (LED type), metal casing also 'earthed'. This gave the same surface voltage, etc and also glowed slightly even when switched off. Hmmm.
I've 'fixed' the problem temporarily simply by running a wire from the a switch plate on the circuit to a plug earth. This has completely fixed the problem for now, removing all voltages and stopping the outside light glowing.

From this it appears that "Equipotential Bonding" has now been achieved, which is good.


I might observe, at this point, that "Earthing" may be a misnomer.
One main point of "Equipment Earthing" is to Bond all external conductive objects to a "Common" Earthed/Neutral connection.
It is the Bonding together of all such "conductive objects" - to the Neutral (return) Conductor
and
to any other extraneous "Earthed" objects (such as Water Pipes)
which is important.

It does seem (to me) that TT Earthing fails in this regard - if that is the "Earthing System" employed in this case.
(See https://en.wikipedia.org/wiki/Earthing_system )

 

[EFLImpudence]

From this it appears that "Equipotential Bonding" has now been achieved, which is good.


I might observe, at this point, that "Earthing" may be a misnomer.

Are you sure?

One main point of "Equipment Earthing" is to Bond all external conductive objects to a "Common" Earthed/Neutral connection.

Not really. It is to ensure operation of the protective device to disconnect the supply

It is the Bonding together of all such "conductive objects" - to the Neutral (return) Conductor
and
to any other extraneous "Earthed" objects (such as Water Pipes)
which is important.

Only parts which are already earthed (might) require bonding.

 

[Harry Bloomfield]

One must wonder what is meant by "getting a slight 'buzz'"

You can get a 'slight buzz', from many things, even double insulated, and/or even USB power adaptors. Generally, you can safely ignore it, but if you get a slight buzz from an item, such as a metal switch plate - that ought to be taken as a potentially serious risk, as it suggests the item is either live, or lacking an earth. Serious, in as much as that earth at the switch, could well remain connected to the rest of the lighting circuit, and should a fault develop on any part of that circuit, which makes that earth live - the switch plate will become live too.

 

[securespark]

Going back to the question that started all this:


It is probably more that it (the earth on a lighting circuit) was not necessary.

It is only recently that a regulation was introduced stating that a Circuit Protective Conductor (earth wire) shall be fitted even though not required.

View attachment 393700

From the 14th Edition, 1966:

D.6. At every lighting point an earthing terminal shall be provided and connected to the earth-continuity conductor of the final sub-circuit.

Your quote above appears in my 2008 red copy of the 17th Ed.

 

[JohnW2]

You can get a 'slight buzz', from many things, even double insulated, and/or even USB power adaptors. Generally, you can safely ignore it, but if you get a slight buzz from an item, such as a metal switch plate - that ought to be taken as a potentially serious risk, as it suggests the item is either live, or lacking an earth.

True, but if one has somehow got charged with static electricity, one might get a 'buzz' (and/or even a 'spark'!) because the item you've touched IS earthed.

 

[JohnW2]

From the 14th Edition, 1966: ... D.6. At every lighting point an earthing terminal shall be provided and connected to the earth-continuity conductor of the final sub-circuit.

That's interesting, since it seems to go even further than today's regs, doesn't it? Today, there is a requirement to run a CPC to every point/accessory, but no requirement of which I'm aware to 'connect' it to anything - and nor do many present day 'lighting points' have an 'earthing terminal', do they?

 

[Harry Bloomfield]

True, but if one has somehow got charged with static electricity, one might get a 'buzz' (and/or even a 'spark'!) because the item you've touched IS earthed.

Never a buzz, just a short discharge, but I get your point.

 

[JohnW2]

Never a buzz, just a short discharge, but I get your point.

Fair enough, but I don't think one can ever be sure what people mean when they talk of 'buzz', 'tingle' or even 'shock' - I suppose the common feature being that it is something which 'makes them jump'. If one thinks of it in such terms, it can certainly happen as a result of static discharges and, as I wrote, that is something which can happen if one touches something which is earthed, but not if one touches something which is not earthed.

 

[securespark]

That's interesting, since it seems to go even further than today's regs, doesn't it? Today, there is a requirement to run a CPC to every point/accessory, but no requirement of which I'm aware to 'connect' it to anything - and nor do many present day 'lighting points' have an 'earthing terminal', do they?

Well, all ceiling roses, boxes, pattresses, junction boxes etc have earth terminals. Most other light fittings have earth terminals, even if they are Class II.

Anything that doesn't should have space to tuck in a connector for the spare cpc, or else the fitting will have a lead attached which will go to a junction box and the cpcs will terminate in there.

 

[securespark]

There's also the requirement for continuity of the cpc throughout the circuit.

 

[EFLImpudence]

Most other light fittings have earth terminals, even if they are Class II.

Are you sure about the Class II ones.

Anything that doesn't should have space to tuck in a connector for the spare cpc, or else the fitting will have a lead attached which will go to a junction box and the cpcs will terminate in there.

Surely having a CPC in a Class II item is not desirable.

 

[pete01]

Surely having a CPC in a Class II item is not desirable.

Well it gives you an easy way to continue the earths like in a pendant