Metal kopex and safe zones.

[Deleted member 18243]

Kopex cannot be used as a conductor. The gland has a flexible, swivelling joint in between the two hexagon shaped sections (see RF Lighting's picture) and although the two halves of this joint are always in contact it is effectively a break in continuity, because its resistance will change as it moves.

Kopex is for mechanical protection only.

 

[JohnW2]

Kopex cannot be used as a conductor. The gland has a flexible, swivelling joint in between the two hexagon shaped sections (see RF Lighting's picture) and although the two halves of this joint are always in contact it is effectively a break in continuity, because its resistance will change as it moves.

Interesting.

Kopex is for mechanical protection only.

Yes, but since it's conductive, it presumably constitutes an exposed-c-p which one would expect to be reliably earthed (for the safety of those who might touch it). Are you suggesting that earthing via the gland does not achieve that?

Kind Regards, John

 

[RF Lighting]

You should only use one swivel gland on a length of kopex to avoid this issue.

I try and only use fixed glands when ever possible.

 

[martin43]

This thread caught my eye as I have this situation in my boiler room. It's actually adaptaflex but the principal is the same, briefly it extends a plastic conduit into an enclosure and is put together from the conduit as swivel gland, flexi, fixed gland, anchored by an earth nut with a fly lead to the earth terminal in the enclosure. I don't disagree with previous contributions and I too would not use it as a CPC, however if you cant reliably earth it then its not actually usable at all. So I measured from the earth terminal to the furthest extent of the metallic parts, i.e. beyond the swivel and came up with a figure of 0.06R. Such a low impedance under fault conditions is going to reliably operate the OPD so I am happy to continue to use it. I readily recognise that it has limitations and terminating the glands is sometimes a real pain and most importantly I wouldn't like the swivel gland to form part of the earth path as has been pointed out you can't rely on that resistance remaining constant. However in reply to the RF, personally I think you can use it for cabling outside safe zones.

Regards
Martin

 

[EFLImpudence]

....

 

[EFLImpudence]

You cannot - there is no argument.

543.2.3 says flexible conduit cannot be used as protective conductor

522.6.204(i) says only a metallic covering which does meet the requirements of a CPC of the circuit comply.

 

[JohnW2]

However in reply to the RF, personally I think you can use it for cabling outside safe zones.

I'm not so sure of that (regs-wise). As others have pointed out, to be an acceptable earthed metallic covering for use with a buried cable outside of safe zones, the regs require it to be compliant with the requirements for a protective conductor - which, in turn, say that flexible conduit cannot be used as a protective conductor.

I'm not sure that necessarily corresponds all that strongly with common sense (although I guess they fear that flexible conduit could break, and hence lose earth continuity), but it appears to be what BS7671 says.

Kind Regards, John
Edit: I must go on a 'fast typing' course

 

[martin43]

I fear I have dropped one here, my apologies. For some reason i didn't connect safe zones and buried cables which displays my lamentable lack of domestic knowledge, my experience being industrial where everything is in view. I did consult the yellow book which of course confirms EFL and JohnW2 correctness. Off to eat humble pie.

Thank you for putting me right.

Regards
Martin

 

[RF Lighting]

That's the whole point of these forums. You've asked, thought, researched and learnt something.

Remember, there's no such thing as a stupid question. Stick around and you'll be amazed what you'll learn.

 

[EFLImpudence]

Remember, there's no such thing as a stupid question.

If dolphins are so clever, why do they live in igloos? South Park