extractor fan wiring problem

[Come on Dave]

Any suggestions anyone please?............
I had an extractor fan installed 4 years ago in a new downstairs loo. It was a timer fan which came on with the light switch. It worked fine for 4 years then broke, so I bought a new timer fan which I assumed would be a straight swop - I installed it and it doesn't work. I'm not an electrician, but I have put in a few timer fans over the years with no problem.

So I have checked the supplies to the fan with a multimeter and I have power to the switched live when the light is on (as would be expected), however there is zero voltage at the permanent live supply. If I turn off the light I then have power at the permanent live. Surely the permanent live should always have power? As I said the old fan was quite happy with this arrangement, but the new one isn't!

Can anyone explain this or suggest how this can be sorted out? I have talked to the electrician who did the initial installation - but he is too busy to come right now to look at it.

 

[CBW]

Have you mixed up the permanent live and switched?

 

[Come on Dave]

No can't be that Chris

 

[EFLImpudence]

The fact that the permanent live isn't live could be why the old fan stopped working.

You will have to find out why it is not live.
Check the other end of the wire which will be at the light or the switch.

 

[Come on Dave]

Thanks, yes I'll do that. Actually I physically broke the old fan - it had started vibrating noisily so I tried to check the visible screws were tight and in the process the fan mountings broke! So I don't think an electrical reason.

 

[oldbutnotdead]

Possible someone has been a bit clever with the wiring and used the 2nd pole of a 2 way switch to provide the 'permanent' live. Or someone has been very bad and put a switch in the neutral instead of the live (not sure how or whether the old fan would have worked in either scenario but since you didn't install it you need to be investigating and testing from first principles)

 

[EFLImpudence]

Neither of those things would have worked.

 

[Adam_151]

Have you mixed up the permanent live and switched?

Or the switched live and the neutral, given that permanent live appears to only be live when the light is off, its not, its just that with your other probe on sw-l instead of neutral, its at the some potential when the light is on

 

[Come on Dave]

Many thanks oldbutnotdead and Adam for your suggestions. No the second pole of the switch has not been used at all, and the wire into the switch is brown. The cable to the fan is 3-core and earth, and the correct colours. With the light switch on I do have voltage between black and grey, but not between black and brown. With the light switch off I do have voltage between black and brown.

At the isolation switch the wires in and out are correct ie greys, blacks and browns. What is confusing me is the light switch, where all the neutral wires are joined in a block, and the grey wire also seems to be joined into that block! I'll investigate further tomorrow or Sunday.

 

[Johnmdc]

It there a voltage between brown and grey?
If so then the grey is neutral (as it should be anyway) and black is switched live.

 

[EFLImpudence]

The cable to the fan is 3-core and earth, and the correct colours. With the light switch on I do have voltage between black and grey,

Right, that's as it should be. Switched Live On to Neutral

but not between black and brown.

That's because they are both at 230V. Switched Live and Permanent Live.

With the light switch off I do have voltage between black and brown.

Have you written that correctly?

With switch OFF you should be measuring Brown-Grey 230V and Black-Grey 0V.

At the isolation switch the wires in and out are correct ie greys, blacks and browns. What is confusing me is the light switch, where all the neutral wires are joined in a block, and the grey wire also seems to be joined into that block! I'll investigate further tomorrow or Sunday.

That will be correct - Neutrals aren't connected to such switches.

It does confirm the Grey is the Neutral

 

[Come on Dave]

Many thanks everyone, especially John, Adam and EFLImpudence, and well done for working out what I had done wrong - ie mix up the black and grey wires. Feeling stupid now! Why was I so convinced that the grey was the switched live? I was perhaps thrown a little by the visible internal wires within the fan using grey for the switched live, but that is really no defence.
Anyway I appreciate you taking the time to explain it to me.
regards, dave

 

[opps]

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