Thoughts on earth bonding on lights please

[stillp]

I'm afraid you've just proved that common sense is misnamed.

 

[JohnW2]

I'm afraid you've just proved that common sense is misnamed.

Maybe. However, speaking personally, if I had a need for an 'insulator' to provide electrical 'insulation' then, quite apart from any regulations and Standards, I would have a fairly good idea in my mind of the 'performance requirement' (in relation to electrical insulation) needed/wanted for my purpose, and I doubt that materials that were deliberately made to be significantly conductive would satisfy that requirement.

Kind Regards, John

 

[stillp]

But you're not an electrical engineer. Would you care to quantify "significantly conductive", or specify a resistivity, or even a voltage at which the conductivity was "significant"?

 

[JohnW2]

But you're not an electrical engineer.

Exactly - and, despite that, I would have pretty good idea of the minimum 'performance requirement' for my purpose. That was really my point in talking about myself.

Would you care to quantify "significantly conductive", or specify a resistivity, or even a voltage at which the conductivity was "significant"?

It would obviously depend upon many factors, particularly the actual situation in question and the reason that insulation was needed. The second question is really a no-brainer - my requirement would obviously be for it not to be "significantly conductive" at a voltage at least somewhat above the highest voltage to which it could be subjected in service. The question of what I would regard as "significantly conductive" really would depend on the application - but I might well look for guidance to what the Standards for electrical cables etc. deem to be adequate for the insulation of live cores at the voltage in question.

Kind Regards, John

 

[securespark]

I've run out of popcorn...

 

[JohnW2]

I've run out of popcorn...

Maybe you should get some more stock in - this isn't the first time we've had this discussion (inevitably started by someone complaining about the 'incorrect' mention of "double-insulated cables"), and I doubt that it will be the last!

For what it's worth, my suspicion (which, as always, may be wrong) is this ... even if it is not 'required', I strongly suspect that the sheathing of PVC/PVC cables probably would pass the insulation test required of the inner insulation - and, if that is the case, then it would not seem unreasonable to refer to it as 'double insulated'. There might well be requirements for the physical properties of the sheath over and above requirements for the core insulation (e.g. resistance to abrasion, UV, chemicals etc., and maybe properties such as flexibility), but that's a different matter.

Again for what it's worth, I think that most people here, including electricians, nearly always seem to talk about, say, "DI singles", with "insulated and sheathed" very rarely written - and we certainly then all know what is being talked about (and would have no problem buying things called "DI singles" from a supplier).

Kind Regards, John

 

[securespark]

Yes, I'm guilty of calling them DI cables, but I do get shot down, often by Risteard...

[ducks]

 

[JohnW2]

Yes, I'm guilty of calling them DI cables, but I do get shot down, often by Risteard...

Yes, in relation to this issue, it's more often than not Risteard who takes people to task.

IF (and I still don't know for certain) the sheathing does/could qualify as 'insulation', then I think this is very different from the "transformer" issue. With the latter, is is very possible to argue (albeit with some dissenters) that SMPSUs are, technically, simply not 'transformers' in the sense that word has been used in electrical circles for decades. However, IF the sheath of a cable qualifies as 'insulation', then there would surely be nothing technically wrong with describing a cable as "double insulated" if it has a layer of such insulation in addition to the insulation around the core?

The argument here seems to be all about whether sheathing is 'required' to qualify as 'insulation', rather than whether it does so qualify - but, without access to relevant material, I do not know the answers to either of those questions with any certainty.

Kind Regards, John

 

[stillp]

The argument here seems to be all about whether sheathing is 'required' to qualify as 'insulation'

If sheathing was required to pass the tests for insulation, why would it be called sheathing and not insulation?

 

[JohnW2]

If sheathing was required to pass the tests for insulation, why would it be called sheathing and not insulation?

Perhaps because, as I have suggested, even if it were required to pass tests in relation to insulation (as you are aware, I don't know), to be acceptable as sheathing (rather than 'just insulation') it is possible that it might also have to comply with additional requirements as regards other physical properties. In other words, it's not impossible (again, I just don't know) that what we use as sheathing would be acceptable as insulation, but not necessarily vice versa.

However, this whole discussion is speculative, on the basis of what the Standards might or might not require, and what properties the sheathing used in cables might or might not have. Unless/until someone can give us definitive answers to those questions, the discussion cannot reach any conclusions.

Kind Regards, John

 

[stillp]

OK, I'll see if I can access a copy. Watch this space.

 

[JohnW2]

OK, I'll see if I can access a copy. Watch this space.

Many thanks.

Of course, the Standard(s) only address one of my two questions - the other relates to what properties the sheaths actually have, regardless of what is 'required' of them. ... it would, of course, be possible for the sheaths to be 'insulating' even if that went beyond the minimum spec required by a Standard.

I'm not sure exactly what Standard you will be try to get a copy of, but, as I said, several of the insulated and sheathed singles I looked at stated that the sheaths were to BS EN 50363-3. Interestingly, in passing, the Prysmian ones I saw had Part Numbers including "SDI" - which, according to their Glossary, means "Single-core Double Insulated".

Kind Regards, John

 

[stillp]

I thought BS6004 would be the most appropriate.
There's nothing to prevent Prysmian exceeding the requirements of a standard.

 

[JohnW2]

I thought BS6004 would be the most appropriate.

I wouldn't know. All I can tell you is what I have already said - that the 'insulated and sheathed' single-core cables I looked at said that the sheaths were to BS EN 50363-3. Whether that Standard has a lesser or greater requirement than BS 6004, I haven't got a clue.

There's nothing to prevent Prysmian exceeding the requirements of a standard.

Indeed. There's obviously nothing preventing any manufacturer of anything making a product which exceeds the requirements of relevant Standard(s). That's why I had the two questions. Even if you discover that the Standards do not require the sheathing to have demonstrated insulating properties, that would not necessarily mean that none of the products out there have sheaths that would qualify as 'insulation'.

Kind Regards, John

 

[securespark]

I can't find BS EN 50363-3 in the Big Green Book...