Thoughts on earth bonding on lights please

[ericmark]

The lamp was fitted to a house wired in 1954, so original no earth, it has a metal eye bracket which screws into the ceiling which has an earth connection, but the light is suspended by a chain which is coated with a bronze looking finish, and two core cable from the metal eye bracket onwards.

I have seen many lamps with this type of connection, and question arises is there really any earth connection through a coated chain or is the earth just some where to terminate cables?

As not new any double square on the box is long gone, there is a double square on the bulb holder, but as to if that refers to whole lamp or just the bulb holder is anyone's guess.

The lamp is heavy and there is a silly post for first part of the fitting which I intend removing, I intend to replace the ceiling rose with a ceiling rose with hook which slides in so it can be all pre-wired on the ground and slid into position all wired up.

Not got the Maestro Ceiling Master rose yet, but it says metal parts so I assume the hook will be earthed, however the whole idea of taking and earth through a chain seems wrong to me. Lifting the lamp either as original or new set up will disconnect the earth even if it does have an earth through chain which seems unlikely due to coatings on the chain and hook.

I personally think the cable is double insulated and holder is double insulated so there is no need for an earth connection. However would like to hear what others think. The only real way to get an earth to the lamp is to swap the cable for three core and fit a brass lamp holder which seems to be going OTT.

It takes a E27 lamp. I will guess from some where like Ikea it looks like the typical Ikea bulb holder.

There will be an earth connection at the rose, as house now re-wired, but I feel the earth connection is only a place to connect the wires to in order to maintain earth connection to next lamp.

 

[Lectrician]

The chain could never be used as a CPC.

If the lamp holder is double insulated, twin flex is fine.

 

[EFLImpudence]

Agree.

If the lamp holder is double insulated, the construction of the rest of it makes no difference does it?

Just to point out - it wouldn't be bonding, in our terminology, as in the title.

 

[Risteard]

I personally think the cable is double insulated

The cable definitely won't be double insulated - although it may well be insulated and sheathed.

As said, bonding doesn't come into it.

 

[JohnW2]

The cable definitely won't be double insulated - although it may well be insulated and sheathed.

... and if it were not insulated and sheathed, then there would presumably be a problem.

Interestingly, the sort of singles used for meter tails and distribution circuits (and for the incoming supply in properties like mine) are widely described as "double insulated" - so I wonder whether the outer PVC layer actually is specified as adequate to provide 'insulation'??

Kind Regards, John

 

[Risteard]

... and if it were not insulated and sheathed, then there would presumably be a problem.

Not necessarily. Hundreds of thousands of miles of non-sheathed singles are installed in containment each and every year.

 

[Risteard]

I wonder whether the outer PVC layer actually is specified as adequate to provide 'insulation'??

It isn't. It might be made of insulating material, but its properties are unverified - it is merely there as mechanical protection to the insulation.

 

[JohnW2]

It isn't. It might be made of insulating material, but its properties are unverified - it is merely there as mechanical protection to the insulation.

That's true of most other cables (T+E, flex etc.), which is why they are not (except in error) described as "double insulated". However, the singles I'm talking about are, as far as I can see, nearly always described as "DI", so I wondered if the situation was different with them.

Kind Regards, John

 

[JohnW2]

Not necessarily. Hundreds of thousands of miles of non-sheathed singles are installed in containment each and every year.

You seem to be ignoring the context - I don't think that a cable wrapped around a metal chain could be described as "in containment"

Kind Regards, John

 

[EFLImpudence]

In situations where we aren't allowed to use single-insulated conductors - i.e. outside of containment - what do we use?

 

[JohnW2]

In situations where we aren't allowed to use single-insulated conductors - i.e. outside of containment - what do we use?

"Insulated and sheathed" ??

I don't know enough about the relevant standards, of which there are different ones for insulation and sheathing of cables (e.g. BS EN 60228 for insulation and BS EN 50363-3 for sheathing). Risteard clearly believes (and may well be right) that the requirement for sheathing does not require verification of adequacy as 'insulation'. However, for all I know, "sheathing" might be required to have the same insulating properties as "insulation", but to also have additional mechanical properties.

I think we need stillp?!

Kind Regards, John

 

[Risteard]

nearly always described as "DI", so I wondered if the situation was different with them.

No. Their construction is no different to that of T&E. It's just an incorrect label frequently applied to them.

 

[JohnW2]

No. Their construction is no different to that of T&E. It's just an incorrect label frequently applied to them.

I'm still wondering. Although I don't have access to the Standards concerend, I have found quite a few cables for which the PVC covering the cores and the PVC sheathing are both described as "to BS EN 50363-3". If that is enough to verify that the stuff around the cores qualifies as "insulation", then such cables presumably really are "double insulated"??

Kind Regards, John

 

[EFLImpudence]

What exactly is being discussed?

Is it just the name of the cable we use when single-insulated conductors would not be compliant?
That is, when s.i. is inadequate, we use insulated and sheathed - so is there no such thing as double-insulated cable?
If so, then there seems to be little point in arguing about or differentiating between 'insulated and sheathed' and 'double insulated' as there is either no such thing as d.i. cable or i.&.s. achieves the same result.

Is it a case of a another poorly chosen alternative description for Class II appliances leading to the confusion?
After all, there are no Class II cables.

 

[JohnW2]

What exactly is being discussed? Is it just the name of the cable we use when single-insulated conductors would not be compliant?

Good questions. Yes, I would say that it's one of those pedantic/terminological quibbles which often pops up whenever someone mentions "double insulated" (similar to when "transformer" is mentioned!).

....That is, when s.i. is inadequate, we use insulated and sheathed - so is there no such thing as double-insulated cable?

As I said, it's just a quibble. In terms of English, "insulated and sheathed" cables presumably are "double-insulated", since the sheath, as well as the inner 'insulation' is constructed using what most people would regard as an 'insulating material'. Risteard's point seems to be merely that he believes that the sheathing is not required to satisfy a Standard as regards its insulating properties in the same way as the inner insulation does. As I've said, not having access to the relevant Standards (and, stillp, no, I'm not going to spend half a day driving to my nearest serious library to look at them), I don't even know if he's correct. I would personally have expected there to be some requirement in the Standard as regards the insulating properties of sheathing - since, unless it were designed to be earthed, I would not have expected it to be acceptable for sheathing to be made out of material which had any appreciable conductivity.

If so, then there seems to be little point in arguing about or differentiating between 'insulated and sheathed' and 'double insulated' as there is either no such thing as d.i. cable or i.&.s. achieves the same result.

There's certainly no point in arguing/quibbling - since, as you say, we use what is available, and that is generally described as "insulated and sheathed" - and, as I've said, I just don't know whether, in terms of regulations and compliance with Standards it would be equally permissible to describe it as "double insulated".

So, yes, I would personally describe it as a terminological quibble that is not worth arguing about. However, as with all these terminological/semantic issues, I have no doubt that there are some (presumably including Risteard) who feel that it is a matter of "people using incorrect terminology" who need to be corrected and educated, even if "we all know what they mean"! Have you not also been known to take that position in relation to similar issues?

After all, there are no Class II cables.

That actually raises an interesting point. With equipment, an alternative to "double insulation" as a means of achieving Class II is to have "reinforced insulation" (which, in practice, often seems to simply mean 'thicker'), but there is no corresponding provision in relation to cables.

Kind Regards, John