DIY Doctor

query : Light fitting / conduit / cable extension

Postby robertg75 » Fri Dec 14, 2007 11:41 pm

Hi all,

I have a query and I'd really appreciate some help please...

I live in an old two-storey house in Scotland, and the lighting wiring is contained in metal pipe conduit. The pipes are screwed into circular metal housings where the wires drop (and return) to the wall switches.

The conduit contains seperate pvc coated single-core wires for live, neutral and earth. There is no "twin & earth" cable anywhere in the lighting circuit.

I need to reposition a light fitting on a downstairs ceiling, but there's not enough wire length or pipe to go with it. The location of the switch will not change, it's just the actual light fitting.

I can't find suitable pipe, so I'm wondering if it would be acceptable if I removed the short length of pipe and three single-core wires from their housing and replaced them with a suitable length of twin-and-earth.

The problem is, that there is only a switched live and earth coming from the down-pipe, the neutral emerges from another pipe that is screwed into the side of the housing, so only the live and earth from the new cable would go down to the switch, the neutral would need to be joined in the housing using connector block. Is this acceptable? Or could I even join the three pairs in the housing, leaving the current switch wires in place?

I can't find a suitable junction box that will connect with this pipework, else I'd have a solution (I think!).

Thanks for taking the time to read this. I hope you can help. If any more information is needed, or even clarification, please let me know.

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Simply Build It

Postby 333rocky333 » Sat Dec 15, 2007 3:51 pm

you may have old three quarter inch pipe , whereas now 20 mm is used there is a range of conduit boxes from 1 to 4 outlets and lids and 4mm screws etc ,either black enamel or galv, now made in the 20mm size.
you just buy a 3/4 to 20mm adaptor or vise versa to make up what you require , screw in tight for earth continuity and there is a earth terminal in addition,located within the conduit boxes, which you should use if neccesary, if so you will also need a 4mm brass screw and lug for that
Any good elect wholesaler should stock them.
If it is really old it may be even smaller pipe ,then you may struggle to get an adapter.
If it is just going to the light , not continuing on and the metal is NOT being relied on for earth continuity to that light you may be able to use the adapters to join to 20mm plastic pipe which is easier to work with.
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Postby robertg75 » Sun Dec 16, 2007 8:33 pm

Hi there,

Thank you very much for your help.

The pipe is the older type, with the smaller diameter, but I was lucky because a neighbour had electrical work done on his house a couple of years ago and kept bits of the old conduit that had been left behind, in the garage.

I found a bit long enough and managed to form it along the route and as it turned out, the wires were actually long enough to make it to the new location as well. I screwed everything up tight, made the connections (including an earth to the pipe) and everything is working fine.

Thanks again!

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