Really Puzzled About Wiring for Extractor Fan in Bathroom!

[jrh1966]

This really should be simple... I thought...

I have an extractor fan (switched with the main ceiling light) in the bathroom which has died some time back. On removal, I find that it is fed by two cables coming from the wall - each with a black and a red core (and no others). So one cable, with a black and a red - and same for the other cable.

Both reds went into the live terminal (red) input in the old fan, and one black went to neutral input (black), and the other black to the third terminal in the connector block, which is yellow. The fan has a timer.

I have bought a new fan - and there are three terminal inputs. Live, Switch Live, and Neutral.

I cannot for the life of me figure out which of the 2 reds and 2 blacks from the wall cables should go where.

I don't mind calling an electrician - but I had expected this to be very simple and a 'like for like'. But it seems not.. or maybe it is - but I cannot figure it out for sure and I don't want to make an error.

Can anyone advise? I'd be very grateful.

Many thanks indeed.

 

[Chri5]

As you say one cable will be the Live, Neutral and earth / CPU and the other will have a switched live.

Have you a multi meter? are you ok with working live?

If so you will find the switched live when the light is on is live, when the light is off the same core will be dead.

Generally I don't like DIY ers working live, if you have any doubts pay a sparks to do it, next time you might want to mark the cables with a sharpie to make sure everything taken off is id'd.

 

[jrh1966]

Many thanks Chris - I have figured which is the switched live - but I still am not sure where the 2 blacks should go. Do they both go in the same neutral on the terminal / input block? When I do that the fan just comes on all the time (without the light on) and when I do turn the light on, the breaker goes at the consumer unit. I am worried that I don't know what I'm doing!

 

[PrenticeBoyofDerry]

Does the fan have an isolator fitted in circuit?
Did the previous fan have an overrun on it that was working?
What cables do you have connected up at the light and switch?
Don't take for granted that the cables are configured correctly, the person who fitted the fan may have used two cable pairs, instead of a three core cable and you may have a spare core.
Is there no earth(CPC) connection or cables?
You need find out which of the cables are permanently live, switched live and neutral.
I'l take a stab that the two reds are permanently live, one black is switched and the a second neutral. They should be marked up and identified to avoid confusion.

 

[EFLImpudence]

Both reds went into the live terminal (red) input in the old fan, and one black went to neutral input (black), and the other black to the third terminal in the connector block,

I have bought a new fan - and there are three terminal inputs. Live, Switch Live, and Neutral.

It's exactly the same.

One of the BLACKS will be the switched live.

Put both reds in the permanent live.
Find which black becomes live when the fan switch is on - switched live - should be sleeved red.
The other black will be neutral.

 

[PrenticeBoyofDerry]

Many thanks Chris - I have figured which is the switched live -

I don't think you have

but I still am not sure where the 2 blacks should go. Do they both go in the same neutral on the terminal / input block?

No

When I do that the fan just comes on all the time (without the light on) and when I do turn the light on, the breaker goes at the consumer unit.

it will, you are making the circuit and shorting the circuit, with what you are doing.

I am worried that I don't know what I'm doing!

You are incorrectly terminating the permanently live (two reds) and the switch live and neutral (two blacks). Ideally you need a multimeter to confirm the function of the cables and mark them up once ID'd

 

[jrh1966]

Guys - massive thanks, much appreciated - all sorted. Your conbination of comments has led me to understand now, and resolve. One of the things that was misleading me was I was expecting switch-LIVE to be red, but it was black.

All sorted, and now I going to the kitchen for a somerset farmhouse cider... mmmm..

thankyou guys again.

 

[PrenticeBoyofDerry]

In an ideal world/installation, both live and switch live would be red. But as twin and earth was/is the common choice of cables within domestic installations and the core colours are often represented red for live and black for neutral, but alas the black core is not always used as the neutral conductor but as the switched live, this should be marked up with a red PVC sleeve or at least some red insulation tape for identification purposes.
Also in an ideal world, I to would be reaching for the farmhouse cider