Is this allowed? - Adding a new cable.

I currently have an extractor fan and one ceiling light controlled by one light switch. One metre or so above the switch is the feed which comes from a fused switch. I want to split the fan and light to be independantly switched so last night tried to put another single wire behind and down the plasterboad wall from the fused switch down to the light switch. Even though I fed the correct amount of wire down, it wouldn't come out the light switch hole.

As there is currently 2 core (red and black/red sleeving) wire already in place, can I use that as a means to pull three core wire down the hole to replace the two core? The new three core wire though is brown, blue and earth. If I can get it down behind the plaster board would it be alright to use the brown as common, blue as one switched live and the earth as the other switched live, if I labelled them correctly?

Thanks david.

djheath said:

As there is currently 2 core (red and black/red sleeving) wire already in place, can I use that as a means to pull three core wire down the hole to replace the two core? The new three core wire though is brown, blue and earth. If I can get it down behind the plaster board would it be alright to use the brown as common, blue as one switched live and the earth as the other switched live, if I labelled them correctly?

Click to expand...

Yes, and no. You can use the 2 core as a draw wire to pull in a new cable, but you run the risk of losing both cables somewhere in the wall if you don't attach them together properly or they get stuck.

You CANNOT and MUST NOT use the earth core for anything other than earth. Get yourself some triple + earth cable and do the job properly.

Thought as much

Triple plus earth!

Righto to the shop it is then.

Thanks for your help.

If you are going to try and pull the cable through you need a plan B because it may get stuck or break at the join.

For plasterboard walls I've had success with thin whippy timber mouldings like 3/8 quadrant which is very bendy - drill a small hole in the end and attach one core to it.

Its quite a bit easier with studs rather than dot and dab, because if the worst happens you can cut a hole over the baton to thread the cable and make good afterwards - less good if your wall is papered

And of course there is the old metal coathanger dodge.

Good luck

Yeah, my backup plan is as follows:

1. Try wire to wire.
2. string and weights
3. coat hanger
4. bits of pipe to feed wire down,
5. chisel + hammer. Remove bits of wire, string weights stuck coat hanger from wall. Fit conduit and add wire properly. Plaster over.
Drink beer, job done!

I hope I only have to do No. 1!

Cheers.

Might I suggest wire to woven polyprolyene cord first - thick version of the stuff used to hang pictured. Its much easier to make a thin smooth join to this than wire-to-wire.

This stuff:

http://www.artestuff.com/product_info.php?cPath=1_39&products_id=212

you can probably get it or something like it in BnQ

Then use the cord to draw the new cable.

Tape the leading end of the new cable to form a pointed end wth out sharp edges that might snag and jam on something.

Add a string or other pull cord tied to the old cable wire so if the cable to cable join breaks there is still a draw cord.

Have one person pulling and another feeding the new cable into the hole but NOT pushing it. Push it and it kinks and makes things harder.

Unwind it by turn the reel so it doesn't have any twists in it./

Also if it is a bit hard to pull through the new cable pull an extra metre of cable through and inspect that to see if any cut or abrasions have happened as it was pulled through.