(Probably a simple) wiring question

[FoxtrotOscar]

Hi

I'm trying to find the simplest way to take a permanent and switched live off my lighting circuit for an extractor fan. I was going to splice into the feed in the loft and use a junction box of some kind. However upon opening up my light switch I found an interesting arrangement, including a single core red wire and a twin and earth but with two brown cables:

What's likely to be going on here? Have they used the light switch as a junction box to take a permanent live off to somewhere else?

I was going to base my wiring on this:

...but why bother with a junction box when I can presumably take both switched live for the fan and permanent live for the fan run-on from the light switch? The only thing I'm struggling with is the neutral back from the fan, but presumably I can run single core flex from the fan neutral to one of the downlight boxes?

Thanks.

 

[PrenticeBoyofDerry]

You have
*1&2 will likely be perm lives in the com of the pull switch
*3 is switch live at L1 of pull switch
This would need confirming via an approved voltage indicator, if you have not got one, stop now and purchase one.
* Then the CPC/earth, I would advise routing one throughout the additional part of the circuit for ex-fan, as this maybe required now or maybe required when replacing ex-fan in future, also helps when testing and fault finding.

A neutral will be at the lighting point take it from the first intersection before first light if a number on a chain, you will also find the switch live at the light fittings, but the perm live is at the pull cord!
All joints made most be accessible for maintenance and inspection/testing.
If they cannot be made accessible for this, then a method considered as maintenance free(MF) must be applied. You can make the joint MF by either using special methods of termination or using MF junction boxes.
Work within the zones in bathrooms require building control notification in England/Wales, they will also require to be signed off and a certificate, either minor works or electrical installation issued.

 

[FoxtrotOscar]

Thanks for the reply, it's led to another question!

Why would there be two perm lives going into the switch? Surely each switch only needs one perm live? Maybe it's be easier to leave the switch alone and take off from the lighting circuit elsewhere.

I have a digital multimeter and I'll use that to test the terminals.

No earth is required for my fan but I'll run one anyway and terminate near the fan.

Any junction boxes will be readily accessible in the loft space.

I'm not doing any work in the bathroom, since the fan is in-line and will sit in the loft void. The light switch is outside the zones.

 

[AndyPRK]

Is it an old house ? 1960's

 

[PrenticeBoyofDerry]

Why would there be two perm lives going into the switch? Surely each switch only needs one perm live? Maybe it's be easier to leave the switch alone and take off from the lighting circuit elsewhere.

There are a number different methods when wiring lighting circuits, in your case visually it looks like the cables numbered 1&2 are what is known as looped in, one comes from another lighting accessory and the other goes to another lighting accessory, if you disconnected the pair from the pull cord one will only actually perm live, but you will have power loss further along the circuit. But you must check this first via an approved tester.
As it could be that the switch is operating two fittings and therefore the single cable marked 3 would be perm live.

I have a digital multimeter and I'll use that to test the terminals.

Thats fine, you will be using the earth as a reference point.

No earth is required for my fan but I'll run one anyway and terminate near the fan.

A CPC/earth is required by BS7671 though. So best to run one, just sleeve it and terminate it into a connector and it does help when it comes to testing.

Any junction boxes will be readily accessible in the loft space.

They need to be accessible for inspection and testing, that is the key thing, not just reachable but you need to be able to stick the probes in and see the results.

I'm not doing any work in the bathroom, since the fan is in-line and will sit in the loft void. The light switch is outside the zones.

I presume you are aware of the requirements for RCD protection for electrical equipment within the bathroom location?
Also permitted routing of cables in walls and through floor joists.

 

[Taylortwocities]

Looking at the age of the wiring, I'll guess that the light fitting only has two conductors going to it?

If so, I expect that (up in the loft somewhere) there will be a big junction box where all of teh lights and switches come together. That is the place that you'll connect up your 3-core & earth for the fan.

That double insulated red is probably an add-on for something back in teh mists of time.

 

[FoxtrotOscar]

Is it an old house ? 1960's

Yep, built in 1959. Has since been re-wired, but they obviously didn't bother with this bit.

I presume you are aware of the requirements for RCD protection for electrical equipment within the bathroom location?
Also permitted routing of cables in walls and through floor joists.

Thanks for this. The switch is operating 6 separate downlights and no other fixture.

I'm using a 3A FCU and the light circuit is protected by a 6A fuse at the consumer unit. Regarding routing cables, I'm running them over the insulation and using clips to attach them to the joists.

Looking at the age of the wiring, I'll guess that the light fitting only has two conductors going to it?

If so, I expect that (up in the loft somewhere) there will be a big junction box where all of teh lights and switches come together. That is the place that you'll connect up your 3-core & earth for the fan.

That double insulated red is probably an add-on for something back in teh mists of time.

The light switch feeds 6 downlights with new scheme wiring, so not sure what's going on tbh. Going to go up in the attic, fight off the cluster flies attacking me, and see if I can figure out how I'm going to wire it. There is a junction box with lots of wires going into it...not sure it will support a three core and earth though . So I might use another junction box after the junction box....

Thanks again for all the help.

 

[Taylortwocities]

There is a junction box with lots of wires going into it...not sure it will support a three core and earth though .

You're going to have to go there to get the neutral from the lighting circuit.

I'm using a 3A FCU

Why do you think you need that?

 

[AndyPRK]

If the 2 browns goto the light you will have all connections you need there.

 

[Taylortwocities]

They won't go directly to the light. They will go to the octopus JB first……

 

[FoxtrotOscar]

Thanks guys. I've got a problem, surprise surprise.

Firstly though, the 3A FCU was because the instructions state it. As it happens I haven't wired it up after all (yet) .

I spent most of the afternoon drilling and running the pipe and wires, etc. I found a junction box for the lights, which as you said had everything I needed...switched L from light switch, permanent live from light circuit, mains neutral and earth.

Now I've come to switch everything back on and...the fan isn't working .

Multimeter says there's 240V across both the permanent live and neutral, and the switched live and neutral, at the three pole isolator. However the same test at the fan terminals gives 240V between permanent live and neutral, but zero V between switched live and neutral (with the lights on).

I've double-checked the wiring at the j/b and am 90% sure the fan is duff, reason being that there's 240V on the OUT side of the isolator which is the last connection before the fan.

Any ideas what's going on? Thanks again!

 

[EFLImpudence]

but zero V between switched live and neutral (with the lights on).

Well, that would appear to be the problem.

I've double-checked the wiring at the j/b

Third time lucky.

aand am 90% sure the fan is duff, reason being that there's 240V on the OUT side of the isolator which is the last connection before the fan.
Any ideas what's going on? Thanks again!

Wire from isolator to fan not continuous.

 

[Taylortwocities]

Maybe, on one of the terminations, the screw is onto the insulation and not on the copper.

 

[PrenticeBoyofDerry]

You did close the switch when testing?

 

[FoxtrotOscar]

Wire from isolator to fan must be continuous surely, or there wouldn't be a potential difference between the perm live and the neutral at the fan? There was 0V between the perm live and the switched live at the fan, which is weird because that would suggest both were at 240V, which if true would suggest a problem with the neutral, yet if the neutral was the problem, I wouldn't have 240V between perm live and neutral!

Regarding the terminating on insulation, I've checked all connection and the only possible terminal that could be connected badly from my testing is surely the switched live at the fan, which I've inspected, removed, stripped and reconnected.

Prentice, do you mean the isolator switch? The isolator was closed when I was testing, as in it was on. When I tested I turned on the light switch and the isolator.

This one has me stumped. Must be a broken fan!