Normally I wouldn't see the need to earth a UB but in this case I'm running some cables through it. I'm planning to use a bit of plastic pipe in the hole to prevent damage to the wire but wonder if I should earth the steel as well.
If so what is the best way to connect the earth wire to the steel? The steel is coated in a couple of layers of intumescent paint for fire protection.
Fash
The beam is not an exposed-conductive-part, probably on two counts: (a) it's not part of the electrical installation and (b) it will probably be enclosed so it can't be touched. Therefore it does not need earthing.
However it may need bonding. If the steel is in contact with the ground it will count as an extraneous-conductive-part and will need main bonding (10 mm^2, usually) - as will any extensive structural steelwork built off the ground, whether accessible or not. This won't apply if the UB is just used as a horizontal beam or lintel to bridge an opening and sits on masonry well off the ground.
(If required) provide a suitable threaded stud on the steelwork, (M10 say) - this could be welded on or could be screwed into a tapped hole and secured by locknuts. Crimp a round lug to the earth wire, sized to match both wire and stud sizes and fasten securely to stud using a lock washer, nyloc nut or locknut etc. to ensure it won't come undone. (Connection to remain accessible for inspection and to be labelled in the usual way.)
"Andy Wade"
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Hmm interesting... So when using Galvanised Capping ...
I suppose it could be classed as part of the electrical installation.
Thanks, Roy
No - assuming T&E cable, properly installed.
It is part of the electrical installation but reg. 471-09-04 states that the use of cable with a non-metallic sheath - i.e. PVC twin & earth - is deemed to provide protection against shock for both direct and indirect contact. Thus capping is not an exposed-conductive-part since it is effectively deemed unable to become live in the event of a fault. Therefore it doesn't need to be earthed, QED.
Yes - but I guess the time when it might become live is when someone drills through it, and the cable it's supposed to be protecting. Mind you, I guess they would have to be pretty determined to get through steel with a masonry bit!
Thanks, Roy
Yes but capping isn't considered to be protection for the cable, other than during plastering operations, so it should only be used in the defined safe zones. Everyone is of course fully aware of these zones and no-one would ever think of drilling in one...
If you want better protection, and/or want your cables to roam free, use earthed steel conduit or put the cables >50 mm deep.
I have a situation where I am taking cable at right angles to a "connection" point, but that connection point will not be visible. Behind kitchen floor cabinet. So I have to protect the cable.
I thought capping was a suitable alternative to conduit. I read 522.06.06 (iii) and thought that capping would provide the necessary alternative mechanical protection to conduit.
Is that not a generally accepted view?
Is steel conduit thicker than capping perhaps?
Can't say that I like doing this at all - but in this case It's a bit awkward to avoid. Hmmm...
Many thanks for your help, Roy
Hmm, interesting question. The regulation does specifically mention "conduit, trunking or ducting satisfying the requirements [...] for a [circuit] protective conductor" for the circuit concerned. Capping is certainly not any of these things, and is very much thinner than the walls of normal conduit tube, or standard metal trunking. The official view, therefore would undoubtedly be that earthed capping would not comply. Nevertheless for the smaller sizes of T&E it almost certainly would meet the CSA requirements for a CPC, so you could argue that it would comply with the /spirit/ of 522-06-06. Then you have the issue of how you make the earth connection - soldering, probably. I think I'll leave you on your own on this one though...
As it's behind a cupboard, could it go on the surface (in PVC mini-trunking, perhaps)?
I bought some capping today - as you say it's far to thin to give the required protection. Back to the drawing board.. Probably have to use conduit.
No no, I didn't explain myself properly...
The connection point is behind a kitchen floor unit. From there the cable needs to go up the wall to the ceiling. So once it's above the worksurface it's vunerable...
Many thanks for your advice, Roy
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