Electrical queries

Jun 24, 2007 6 Replies

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MisterP 19 years ago

This is a 50 year old installation with existing vertical steel ova

conduits to sockets plastered into the walls. The rubber(!) cabl enters from above and there is a grommet inserted into each of th conduits to prevent damage to the cables.

Now if rewired with PVC sheathed cable, then a) Can I re-use the steel conduit? b) Where can I get suitable grommets? These are top hat shaped wit central hole for the cable. c) The recessed steel boxes do not have an earth connection. Can on be fitted or is it better to replace each box?

Many thanks

-- MisterP

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Rumble 19 years ago

MisterP said the following on 24/06/2007 15:35:

Yes.

Never seen 'em for sale anywhere. I'm not saying you will not be able to get them; someone might come along and prove me wrong...

Just be careful when pulling the new cables through (use the old cables to pull the new ones in).

Better to replace each box - not least because the shiny new screws supplied with your new accessories will be metric and the screw holes in your old boxes will be imperial...

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John Rumm 19 years ago

Yes - at least for switch drops. You may have difficulty getting

2x2.5mm^2 T&E through the socket runs, but then again it is possible sometimes using the old cable to pull through the new. (strip the outer insulation at the end of the old and new wires and firmly twist the inners together before taping up. tape the second wire a couple of feet back from the joint of the first and it will make pulling through a bit simpler.

Usually the existing ones stay put and remain serviceable.

As long as they don't have two moveable screw holes then you can rely on the screwed connection from the accessory to earth the box. Often older installs like that will have odd sized backboxes, or wooden ones which need replacing. Needless to say you probably want lots of sockets in positions where there are currently none.

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Lobster 19 years ago

Really? But modern backboxes typically don't have two moveable screw holes, just one; and surely a modern box must always be earthed separately?

David

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Andrew Mawson 19 years ago

screw

Would it be legitimate to fix a crimped earth tag to the back box using either a pop rivet or a self tapping screw ?

AWEM

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Andrew Gabriel 19 years ago

There's no requirement in the regs to earth back boxes unless they are exposed. It's good practice of course, but I wouldn't replace a back box just because it didn't have an earthing point. It would be easier to drill a tiny hole for a self-tapping screw if you really want to do this.

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John Rumm 19 years ago

It is preferable, but not actually a requirement, IIUC.

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