A simple question

[Furthy34]

I have removed a ceiling rose and there are 3 red, 3 black and 3 earth wires and I want to fit a new light fitting.

Normally I would connect the wires as shown on many wiring diagrams on the net and end up with a blue and brown wires going to the new light fitting.

However, in this case the new light fitting has a terminal for an earth presumably because the casing is metal. My question is: -

1) Do I put the 3 earth wires from the ceiling into the terminal on the new light fitting?
2) Or could I simply put the 3 earth wires from the ceiling into a choc block and then run a new earth wire from this choc block into the earth terminal on the new light fitting?
3) Or would either of the above be ok?

 

[John D v2.0]

Either of the above. The important thing is that every termination point has an earth run to it and connected to the other earth wires, and any light fitting that has an earth terminal is connected to the earth.

If you have a multi meter, you can verify by measuring the resistance between the light fitting casing and a metal pipe (gas or water if metal) and the resistance would usually be less than a couple of ohms.

 

[bernardgreen]

One of the Blacks will be the Switched Live and this must not be connected to the other Blacks which are Neutral.

The Switched Live brings Live to the lamp from the switch and will have been connected to the Live of the lamp in the ceiling rose.

Did you know for certain which Black is the Switched Live ?

 

[Furthy34]

Either of the above. The important thing is that every termination point has an earth run to it and connected to the other earth wires, and any light fitting that has an earth terminal is connected to the earth.

If you have a multi meter, you can verify by measuring the resistance between the light fitting casing and a metal pipe (gas or water if metal) and the resistance would usually be less than a couple of ohms.

Many thanks John D, very clear answer.
Why do some light fittings only require live and neutral with the earth wires just coming in and out via a terminal where the old ceiling rose was?

 

[Furthy34]

One of the Blacks will be the Switched Live and this must not be connected to the other Blacks which are Neutral.

The Switched Live brings Live to the lamp from the switch and will have been connected to the Live of the lamp in the ceiling rose.

Did you know for certain which Black is the Switched Live ?

Yes Bernard, I know which is switch live but thanks for your concern. There is a lot of instructions on the internet about recognising and marking this etc. when changing a ceiling rose for a modern light fitting. But strangely I could not find any clear information in a situation where the new modern light fitting seems to require an earth. I am still not sure if it does or not but it has an earth fitting and is metal so I assume that it does.

 

[bernardgreen]

I know which is switch live but thanks for your concern.

Sadly many don't.

 

[John D v2.0]

Many thanks John D, very clear answer.
Why do some light fittings only require live and neutral with the earth wires just coming in and out via a terminal where the old ceiling rose was?

There's a lot of information about lighting circuits online, so read up on it. If your system is looped at the switch you'll have all the connections there and the light fitting is just a dead end for the cable. If it's looped at the light fitting then it will be the other way round.

 

[Furthy34]

There's a lot of information about lighting circuits online, so read up on it. If your system is looped at the switch you'll have all the connections there and the light fitting is just a dead end for the cable. If it's looped at the light fitting then it will be the other way round.

Mine is looped at the light fitting.

 

[John D v2.0]

Mine is looped at the light fitting.

An right misunderstood, it's because the extra terminals cost extra money and are not used in mom UK countries.

 

[SimonH2]

But strangely I could not find any clear information in a situation where the new modern light fitting seems to require an earth. I am still not sure if it does or not but it has an earth fitting and is metal so I assume that it does.

If in doubt, then a metal fitting must be earthed - especially as this fitting does have an earth terminal. There are quite a few fittings where the manufacturer claims that it is "double insulated" (marked with the "square inside another square" symbol) and doesn't provide an earth terminal - but some of those claims look "a bit dubious"

 

[JohnW2]

If in doubt, then a metal fitting must be earthed - especially as this fitting does have an earth terminal. There are quite a few fittings where the manufacturer claims that it is "double insulated" (marked with the "square inside another square" symbol) and doesn't provide an earth terminal - but some of those claims look "a bit dubious"

I totally agree - but, as you aere undoubtedly aware, there are some people, here and elsewhere, (and certainly some MIs) who, for whatever reason, say that a Class II item "must not be earthed".

People with that view will generally cite the (true) fact that to 'unnecessarily' earth anything (be it related to an electrical installation or not) increases hazards - which is true. However, if one has doubts that an allegedly Class II item which has exposed-c-ps actually would be 'safe' with those parts not earthed, then I personally feel sure that to earth them is the lesser of the two risks.

Kind Regards, John

 

[EFLImpudence]

I totally agree - but, as you aere undoubtedly aware, there are some people, here and elsewhere, (and certainly some MIs) who, for whatever reason, say that a Class II item "must not be earthed".

People with that view will generally cite the (true) fact that to 'unnecessarily' earth anything (be it related to an electrical installation or not) increases hazards - which is true. However, if one has doubts that an allegedly Class II item which has exposed-c-ps actually would be 'safe' with those parts not earthed,

By definition, a Class II item does not have exposed-c-ps.

then I personally feel sure that to earth them is the lesser of the two risks.

What you mean is, presumably, items which state they are Class II but which you do not accept.
I.e. items which should require two faults for the metal part to become live but you can see that this is not true, so they would presumably be wrongly described as Class II.

Perhaps there are some such poor products but that does not alter the principle that Class II items must/should not be earthed.

 

[JohnW2]

By definition, a Class II item does not have exposed-c-ps.

One can argue about the definition of "exposed-c-p" (which does not say anything about becoming live under single fault conditions) - but I suppose that, knowing that there were people like you around ( ), I should probably not have written "... an allegedly Class II item which has exposed-c-ps" but, rather, something like "... an allegedly Class II item which has exposed metallic parts which one feels could become live in the case of a fault".

What you mean is, presumably, items which state they are Class II but which you do not accept.

Indeed - since that appeared to be what Simon was talking about when he wrote ...

... There are quite a few fittings where the manufacturer claims that it is "double insulated" ... but some of those claims look "a bit dubious"

Perhaps there are some such poor products but that does not alter the principle that Class II items must/should not be earthed.

If they are truly (not just allegedly) Class II then I agree that it is not necessary to earth them. One can debate (as we often have done) whether that means that one 'should/must' not earth them - although, even if they do have exposed metal parts which one has earthed, they are then no more 'hazardous' then they would have been had they not had 'double or reinforced insulation' underneath the metal (which is why I feel that, so long as we allow Class I items, "must not" is probably a bit OTT).

However, as I thought was clear, that was not what I was talking about. In response to what Suimon has said about 'allegedly {"dubious"} Class II items, I wrote (after presenting 'your argument' for not earthing) "if one has doubts that an allegedly Class II item ... would be 'safe' with those parts not earthed, then I personally feel sure that to earth them is the lesser of the two risks". I still personally stick to that view - since, if one has such doubts, in my opinion the risk of not earthing them exceeds the 'risk' that would arise by earthing them.

Kind Regards, John

 

[EFLImpudence]

It is for you to judge the lesser of two evils, but, then I would suggest that your arguments are the equivalent of Bernard's to earth (wrongly bond) metal parts that do not require it.

The products in question may also be as poorly made in other respects so perhaps a better choice would be to not use at all but send to Trading Standards.

 

[EFLImpudence]

Also -

even if they do have exposed metal parts which one has earthed, they are then no more 'hazardous' then they would have been had they not had 'double or reinforced insulation'

That may be true but it is a false argument because you have made them 'more hazardous' than they are intended to be.

One could remove all RCDs as things would then be no more hazardous than they used to be.