Metal conduit between two light fittings

Is this a real issue, or just an office debate?

What the lamp fittings are made of, even if they are double-insulated, is irrelevant. The risk arises from the cables passing through the conduit.

Hi Chris, It is a real issue, we are installing earths to the ends of the conduits hence why it started the discussion. they area GRP linear fittings the span is approx 1m of conduit at around 3m ceiling height

Ross has summed up the Regs very well. Mind you, I struggle to see how a fault could arise within the conduit unless mice could find their way in.

Would PVC conduit not be simpler?

Hello Chris:

Your question that PVC conduit would be simpler -- is the right answer and cheaper too.

Over here in the US we have flat rectangular PVC conduit 

Peter Brooks

It would be if the conduit wasn't already there. We are simply swapping lights over on an existing installation. The original conduits were not earthed and we connecting fly leads via the lock nuts to the terminal of the fittings. The question was raised in the office weather there was a requirement to do so, but as all here have agreed with the majority of us. It has validated what we are doing. Thanks all!

Hello Mark:

Just for my education "why" and "what" are you swapping the office lights from - to.

Peter Brooks 

The works are in a carpark. Swapping fluorescent linear fittings for LED. The discussion was in the office.

I struggle to see how a fault could arise within the conduit unless mice could find their way in.

Insulation could be damaged when drawing in (and that likely wouldn't be spotted during an insulation test as the conduit wasn't earthed), or the insulation might be deficient due to a cable manufacturing fault. Even if it was perfect when installed, some problems (e.g. small overloads of long duration) can remain undetected for long enough for insulation to soften and conductors creep to the surface (especially if there are bends or kinks in the conductors) or even genuine faults that don't disconnect as promptly as they should (RCDs stick, wrong fuse rating used or DIY extensions to circuits so loop impedances too high).

A few generations ago we used to put cotton covered rubber singles in unearthed steel conduit - (in a way the cotton braid was seen as a sheath and so the steel was for mechanical protection only) ... but there were sufficient problems, even by the safety standards of yesteryear, for the practice to fall out of favour.

   - Andy.

I struggle to see how a fault could arise within the conduit unless mice could find their way in.

Insulation could be damaged when drawing in (and that likely wouldn't be spotted during an insulation test as the conduit wasn't earthed), or the insulation might be deficient due to a cable manufacturing fault. Even if it was perfect when installed, some problems (e.g. small overloads of long duration) can remain undetected for long enough for insulation to soften and conductors creep to the surface (especially if there are bends or kinks in the conductors) or even genuine faults that don't disconnect as promptly as they should (RCDs stick, wrong fuse rating used or DIY extensions to circuits so loop impedances too high).

A few generations ago we used to put cotton covered rubber singles in unearthed steel conduit - (in a way the cotton braid was seen as a sheath and so the steel was for mechanical protection only) ... but there were sufficient problems, even by the safety standards of yesteryear, for the practice to fall out of favour.

   - Andy.

AJJewsbury said:

Insulation could be damaged when drawing in

Point taken, but you would have to be pretty ham-fisted to damage the cables in 1 m of conduit.