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Wiring bathroom extractor to old fashioned lighting circuit

This topic originated from the How to page called Installing wiring for an extractor fan
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exeter

from United Kingdom

Joined: 15 May 2007
Posts: 8
Location: United Kingdom

PostPosted: Thu May 17, 2007 4:13 pm Reply with quote

My lighting circuit wiring is very old. In the bathroom I have three wires, sheathed in fabric that come from metal conduit. One wire is a switch live, another one permanent live and the third is neutral.

In the bathroom light fitting (not loop-in) switch live is in one terminal and neutral and permanent live are joined together in the other. If you disconect permanent live, then the bathroom light will work, but some of the other lights in the flat stop working - so i\\\'m presuming that the permanent live is a circuit cable.

I have an extractor fan with timer which I want to make sure will work before incorporating an isolating switch. I want it to come on with the light switch and over run and I also want the bathroom lights and other lights to work, obviously.

The fan works perfectly if I connect the three wires appropriately, and I presume I could get the bathroom light to work, but because the permanent live and neutral are separated, half the lights in the flat stop working.

What I\\\'m wondering is if there is a way to solve this problem, or should I buy a non-timer fan instead. Would this type of fan only have two terminals - a switch live and neutral?

Could I therefore just extend a twin and earth cable from the light fitting and wire up the fan to work with the light switch, while keeping the permanent live and neutral together at the light fitting?
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davy_owen_88

from United Kingdom

Joined: 17 Nov 2006
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Location: West Glamorgan,
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PostPosted: Thu May 17, 2007 4:38 pm Reply with quote

exeter wrote:
In the bathroom light fitting (not loop-in) switch live is in one terminal and neutral and permanent live are joined together in the other. If you disconect permanent live, then the bathroom light will work, but some of the other lights in the flat stop working - so i\\\'m presuming that the permanent live is a circuit cable.


You do not have a neutral and permanent live in one terminal because that would create a dead short and the fuse/MCB would blow/trip.

Some pictures or a clear explanation of the number of cables present, along with the number and colour of conductors present at the switch and light in the bathroom would help greatly.

By the way. work in the bathroom is notifiable, so before you start fiddling you need to notify your BCO and pay the relevant fees for them to inspect and test.
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jj4091

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Location: Cumbria,
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PostPosted: Thu May 17, 2007 5:16 pm Reply with quote

If you have the old cloth covered rubber cables, then I would not be surprised if the insulation is perished or hard & cracking, personnaly I would not consider doing any modifications to the circuit unless I was 100% certain it was safe, which means having it tested professionally.
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RF Lighting

from United Kingdom

Joined: 31 Mar 2006
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Location: Leeds,
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PostPosted: Thu May 17, 2007 5:37 pm Reply with quote

You need to call an electrician.

If you really do have VIR singles in conduit, then this all needs replacing ASAP

The 'permanant live' is infact a neutral which appears live as you have broken the continuity from the remaing light back to the mains.

No offence but you are way out of your depth.

Please can we have some photos of your wiring and also your fusebox and mains inccomer area so we can get a better idea of what state your wiring is really in.
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exeter

from United Kingdom

Joined: 15 May 2007
Posts: 8
Location: United Kingdom

PostPosted: Thu May 17, 2007 7:01 pm Reply with quote

The sparks from work said he'd take a look.

Rest assured, my consumer unit is of the single-bladed fuse variety and the light switch to the bathroom looks like spaghetti junction. Thankfully it is located outside the bathroom.

They are VIR singles coming out of conduit. The one I referred to as switched live is red, the other two are black. The reason I thought one was permanent live is that when I wired up timed extractor fan, it ran the timer over-run ok, whereas the switched live switched it on.
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RF Lighting

from United Kingdom

Joined: 31 Mar 2006
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Location: Leeds,
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PostPosted: Thu May 17, 2007 7:34 pm Reply with quote

exeter wrote:
Rest assured, my consumer unit is of the single-bladed fuse variety.


So it could be >50 years old. Not exactly very reassuring icon_rolleyes.gif
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exeter

from United Kingdom

Joined: 15 May 2007
Posts: 8
Location: United Kingdom

PostPosted: Thu May 17, 2007 9:28 pm Reply with quote

I was being facetious! The place is in need of a rewire, but until I find the 3-4,000 to do it, the VIR cables and 50 year old fuse box will have to soldier on. Will get it tested before I get any further work done, though.
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