Light switch activating extractor fan in next room

[jsmithy]

Hi

My bathroom is adjacent to my kitchen downstairs in my house. It has an extractor fan which is activated by the bathroom light cord. (When the bathroom light is switched off the fan continues to run for 10 minutes or whatever).

Anyway, recently - I swear it wasn't happening before a few weeks ago - when I switch on the kitchen light in the room next door, the extractor fan in the bathroom goes on!

Can anyone comment on how/why this is happening? FYI the light switch for the kitchen is on one wall. On the next wall nearby, above the doorway to the bathroom, there is an isolator switch for the extractor fan.

I should say that I'm a complete layman when it comes to electrics.

Any help greatly appreciated.

JS

 

[Evans Electric]

If this strange phenomena has only just started...have you had any electrical work done recently ?

Does the bathroom light come on with the kitchen light now?  

Have any switches been removed & re-fitted?  

 

[jsmithy]

Thanks for your reply.

No, I've had no work done and nothing has changed in terms of switches recently. The bathroom light does not come on with the kitchen light now (or vice versa), it's only the extractor fan.

JS

 

[Rrrrr]

Never heard of this before in 30 years!

Does it happen every time?

 

[kerching]

Single fan for two,rooms was common in early 80s

both switches had to,be double pole switches

but if no work has been done then this cannot be the case

just saying

 

[jsmithy]

Does it happen every time?

Yep!

 

[Rrrrr]

If it's only started happening recently and there has been no electrical work done recently then I would recommend you get it checked out

 

[ProDave]

Does the BATHROOM switch still turn the fan on as well?
 

 

[jsmithy]

Does the BATHROOM switch still turn the fan on as well?
 

Yes

 

[Barx]

I would get some testing done at the fan whilst switching switches etc.

Maybe an issue with neutral backfeeding and the fan getting confused.

have you had anything done at all in the house that could disrupt the electrics?

Take lamps out of kitchen and bathroom lights and see if it still does it when you switch.

 

[Murdoch]

Is the fan mounted in the ceiling? I saw a fan with a vertical vent "collect" moisture in the case, enough to connect Pl with neutral!

 

[jsmithy]

Is the fan mounted in the ceiling? I saw a fan with a vertical vent "collect" moisture in the case, enough to connect Pl with neutral!

No, it's not. It's on the back wall next to the window. The bathroom is well ventilated.

I would get some testing done at the fan whilst switching switches etc.

Maybe an issue with neutral backfeeding and the fan getting confused.

have you had anything done at all in the house that could disrupt the electrics?

Take lamps out of kitchen and bathroom lights and see if it still does it when you switch.

Thanks for all your help. We haven't had anything done recently that could have disrupted the electrics.

 

[ProDave]

How old is the house? when was it last rewired?  I might have a theory about what's causing it but would only be likely to be a valid theory if it's an old house with old wiring.....

Related to my theory is a further question. What sort of lamps do you have in the bathroom, filament, halogen, CFL, led etc?

 

 

[jsmithy]

Hi ProDave

The house is an old Victorian terrace, but the bathroom and kitchen are in an extension put on I think about 20-25 years ago. I have no idea when it was last rewired at all as I've not been living here that long.

The light in the bathroom is just a standard fitting with a normal, albeit low energy, light bulb.

J

 

[ProDave]

Okay, here is my theory, and I admit it's a long shot and could be totally wrong.

I suspect the house is wired spider fashion to a big lighting junction box somewhere, and since they were added at the same time, the swichecd L to the kitchen and bathroom are adjacent in that JB.

The JB is full up with dust , dirt, spiders webs and general crud that accumulates. It has somehow also got a bit damp. So there is a bit of leakage between the circuits.

The Switched L into a timer fan is only a signal to some electronics (the actual power to the fan comes from the permanent L via a relay or some other switching device). So the SWL is a high impedance input. Chances are, it will trigger at a lot less than 230V.

So the leakage means there is a stray voltage on the bathroom SW L when the kitchen light is turned on. Not enough voltage to trigger the CFL lamp, and below it's striking voltage the lamp will be high impedance as well, allowing the stray voltage to appear.

Find the JB, clean it all out and the fault will go away.

Ready to be shot down and proved wrong, I did say it's a long shot, but anyone got a better theory? 
 

 

[Lurch]

Why all the random guessing?

This needs looking at, the OP needs to get someone in who knows what they are doing. This is obviously an unusual occurrence and there is no common issue or simple fix. There could well be plenty of other issues with the electrics as well so someone with some electrical knowledge really needs to cast an eye over it.

 

[jsmithy]

Thanks for all your help. I guess I'll get someone to look at it.

 

[ProDave]

Thanks for all your help. I guess I'll get someone to look at it.

Please do let us know what the fault turns out to be.