Main equipotential bonding question

[ban-all-sheds]

Yes.

And you could spend from now until the heat death of the universe arguing that it makes no sense that the regulations on concealed cables apply to those, but it would not make one iota of difference to what the regulations actually say.

 

[sparkwright]

I tend to agree with Ban. The earth cable is part of the electrical installation, so should only be concealed in the same manner that other electrical cables may be installed.

The earth cable if placed behind the skirting/in the gap between flooring and skirting could easily get drilled through, and the damage would go totally unnoticed.

Some tough metal conduit over it would be more satisfying, presumably this wouldn't need earthing...

The comment earlier about D Line trunking being the same as a cable in a gap covered with some beading doesn't compute with me.

Trunking is trunking, no matter what design it is, and is for surface wiring - so this is not the same as concealing a cable with a strip of wooden beading.

 

[JohnD]

but earthed conduit does not resist a drill, its purpose is to provide a path to earth and perhaps blow a fuse or trip a breaker.

If you drill through an earthed conduit and hit an earthed wire, or a telephone cable, the effect will be, er, umm.....

 

[JohnW2]

I tend to agree with Ban. The earth cable is part of the electrical installation, so should only be concealed in the same manner that other electrical cables may be installed. The earth cable if placed behind the skirting/in the gap between flooring and skirting could easily get drilled through, and the damage would go totally unnoticed.

Yes, I can't argue with that. However, as I pointed out to BAS earlier, if it is regarded as 'concealed in a wall', not in a safe zone, one way of making it fully compliant would be to provide it with an "earthed metal covering" - which (in the case of a cable which is just a protective conductor) is obviously plain daft, would not reduce the risk of it being drilled through and would not prevent any such damage going unnoticed. Those who wrote these regs were obviously only thinking about live conductors!

As you say, since there is no way that one could stop the severing of a protective conductor potentially 'going unnoticed', the only way of ensuring that it did not suffer mechanical damage would to be require it to be provided with substantial mechanical protection - substantial enough to prevent penetration by a drill or whatever (since no 'protective device' is going to help).

The comment earlier about D Line trunking being the same as a cable in a gap covered with some beading doesn't compute with me. ... Trunking is trunking, no matter what design it is, and is for surface wiring - so this is not the same as concealing a cable with a strip of wooden beading.

Fair enough, but we can't have it both ways - are you saying that you disagree with RF's comment that "It looks just like regular beading"?

Kind Regards, John

 

[sparkwright]

I'm saying trunking that looks just like regular beading IS trunking, and can be used for that purpose. And that regular beading is not trunking, nor does it resemble a 'boxing', so can't be used as trunking.

I would have thought regular 20mm metal round conduit would provide sufficient protection from drilling.

I take on board the comments about cables not in safe zones can be within in an earthed metal covering. This could include MI or SWA - which would easily get drilled through - yet should activate the fuse or MCB or RCD.

Since no live conductors are in the single earth we are talking about, I would urge the installer to use something like round 20mm metal conduit, which is hard to drill through unless one is determined.

Though it does make you think that it still COULD get drilled through and go unnoticed.

That said, even regular cables in actual safe zones can get drilled through and can go unnoticed...

 

[JohnW2]

I'm saying trunking that looks just like regular beading IS trunking, and can be used for that purpose.

That may well be 'officially' true - but if it really is visually indistinguishable from 'regular beading' (and probably made out of a softer/thinner material than beading), it is not really going to afford any more protection to the cable than would the beading.

I take on board the comments about cables not in safe zones can be within in an earthed metal covering. This could include MI or SWA - which would easily get drilled through - yet should activate the fuse or MCB or RCD.

.. although, as you go on to imply, the protective device would obviously not help when the cable is just a single protective conductor. However, to those like BAS who seem most concerned about compliance with what the regs "actually say", to provide the cable with an 'earthed metal covering' would serve that purpose (even though no practical purpose).

...I would urge the installer to use something like round 20mm metal conduit, which is hard to drill through unless one is determined. ... Though it does make you think that it still COULD get drilled through and go unnoticed.

Few things are impossible, but it would take a significant idiot to drill through any sort of 'unexpected' metal conduit (when (s)he was expecting to be drilling through some other material) without noticing.

As I implied in my last post, there would be a case for the regs requiring substantial mechanical protection for concealed ('lone') protective conductors, since damage to them is much more likely to go unnoticed than is damage to a cable which includes live conductors (and a CPC).

Kind Regards, John