Hi all,
we are having a discussion in the office and wanted your thoughts on the subject. If you have a metal conduit fitted between two plastic light fittings, the circuit is wired in singles (including a separate CPC), is there a requirement to earth the metal conduit?
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.
Hello Mark:
So you were talking about metal Troffers with plastic lens in effectively an outside but covered area.
As a frame of reference I use troffers in my home ,in work areas (family room, kitchen etc) and changed them over from Fluorescent to LED about 5 years ago.
The LED's are on magnetic stripes and the AC/DC Converter is also mounted on a magnetic strip. This allows one to magnetically attach to the metal in the troffer, without any screws.
The new version of the magnetic LED kit which I recently purchased now allows one to switch lighting intensity and color.
Regarding the carpark -- I hope you are not parking EV cars in the closed area"
Peter Brooks
Palm Bay FL
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.
Something tripped a memory about this over the weekend, and following a trip to the archive and going back as far as BS 7671 : 2001 (Amendments 1 & 2) the equivalent regulation to 410.3.9 was 471-13-04.
471-13-04 permitted protective measures against indirect contact to be dispensed with in instances numbered (i) to (vii) one of which was:
'(v) inaccessible lengths of metal conduit not exceeding 150 mm'
If the conduit in the original question has a length ≤ 150 mm and is inaccessible, then it might have complied at one time.
However, the requirement of inaccessibility would be difficult to meet in most situations, as even if the conduit is inaccessible in the normal use of the installation, it is likely to become accessible at some point, for example during maintenance work.
- Ross
Ross, very impressed with your memory! :-)
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