Is it acceptaple to run cables in (probably standard plastic clip on cover) conduit fixed to the underside of exposed joists? I can't see any reason why it shouldn't be OK but want to check.
It's to run a couple of 2.5sq mm feeds across the ceiling of a garage which has a room above it but where the joists are exposed. Going round the edge at the top of the walls is possible but rather messier with obstructions and such (and would also use more cable).
What of the new 18th Ed requirements to fix cables such that they don't droop down in the event of a fire?
Trunking not conduit if it has a clip on cover?
Either is fine but you should put some metal clips/p clips or all round band inside the trunking to secure the cable in the event of a fire.
You could just clip the cable straight across the underside, and then use the metal normally used to protect cables under plaster in protected zones "over" (or rather under?) it, if you see what I mean?. Also a little bit mechanically stronger in the event of accidentally swinging a tool between the joists.
Trunking, yes. Conduit you have to poke it through don't you.
... and yes, thanks for the new 18th edition requirement which means I'll need to put metal clips of some sort round the trunking. Are clips like this now available or will I have to improvise something?
Anything metal will do [1] so use all round band, P clips or google for "clips for trunking" that will bring up some metal U shaped clips designed for trunking.
[1] It probably has to be steel. Sodium and mercury etc just do not cut the mustard:-)
Inside the trunking!
Is there a car in said garage, and what height is it? Brian
If you use 20mm plastic conduit it will take 2 x 2.5 mm T&E, and you can use metal conduit saddles to satisfy the fire support requirements.
Drawback with conduit is that you have to thread the cables through rather than laying the trunking over them.
Owain
Last time I looked, there didn't seem to be any aimed specifically at plastic conduit - I assume one just buys metal conduit clips that's sold for metal conduit...
Yep.
It's a 3 car (wide) garage, there's a motorbike in slot 1, a car in slot 2 and a mower in slot 3. The roof joists are quite high, 2.5 metres or so I would guess.
Doing the voltage drop sums I think I'll probably need 4sqmm, but if I do that I'll only need one (see new thread) cable so it would fit easily in a 20mm conduit or an oval 25mm.
I'm now trying to decide whether to use a single length of PVC T&E with conduit and catenary for the overhead bit or whether to use T&E for the indoor bit and SWA for the outdoor bit. It probably doesn't matter all that much.
You could, but it makes more sense to clip the cable to the sides of the joists without trunking.
NT
The run is *across* the joists, not in the same direction as the joists run.
Any particular reason not to run it naked through 12 mm holes?
300mm max cable support spacing[1]? I wouldn't claim to comply always and everywhere but it'd be a bit obvious in a garage roof. [1] for 10 to 15mm diameter
Fair point, although I don't see much "electrical" risk. I still thing the quickest and easiest way might be to use metal capping as a sort of mini "cable tray".
I'm probably going to take it outside but, if not, I think cable trays will be the way to go, much less hassle than clipping or trunking I think - and looks don't matter in the garage.
cable support is not to deal electrical problems but with the blocking of an escape route by drooping, burning cables. I understood, from a presentation on the new REgs, that a firefighter lost his life having been trapped.
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