Home DIY

Lights and the isolator have both been off for ~10 minutes.

I left the lights off and closed the isolator, and after a delay of 15-20 seconds the fan came on.

The switched live was def off as otherwise the lights would have turned on.

I've left the isolator closed (and therefore the fan on) to see if it turns off at some point.

If that doesn't work, perhaps disconnect the switched live feed and see what happens? Have you checked the wiring with a meter to confirm the switched live is exactly that.
Also is there a jumper in the fan that needs removing for timed operation?

Also, it's odd that it should come on after a delay of 15 - 20 seconds!!??

Yes, it is. The only thing that I could think of was that there might be some strange effect from the 230V to 12V transformers on the lighting circuit, which is connected to the "after light switch" part of the switched live.

6 of those transformer btw, can/could they act as a capacitor of sorts? Enough to provide the extractor transformer with enough current to turn on?

It's got separate power, so the question would be how much power the T needs to see in addition to the mains power feed.

I found this thread whilst searching for "bathroom fan induced voltage" thinking maybe it's picking up something that's trigging the switched feed.
Sounds like we're thinking along the same lines...

The fan ran for 20 minutes, I then turned it off at the isolator as I'm about to go to Muddy Hell

I wonder if there is an electrical equivalent of a plumbing one way valve?!

Possibly
lots on sale on ebay for a good price, i really want it in my room but not sure i can do i properly

Just come in from a long day, here's what may be occuring:

What you think is neutral is at 230V, live is at lower potential. There being no earth reference isn't helping either.

The lamp filament is therefore charging up and reaches live potential, you don't need much potential difference for a 6V transformer to produce enough magnetic flux to start a simple fan.

Or I could be talking bollox.

One important point - having metal termination boxes exposed at the surface of the ceiling or wall, with metallic conduit, using only two circuit conductors and no protective earth, is elevating the risk of both electric shock and thermal degradation.

RG - I will get a meter and check that what I think is live is live, same for neutral.

In terms of the earth situation, the metal conduit was previously earthed - I found the remnants of the earth which had been cut and left hanging.

I'll wire that back to the outer sheath of the mains supply, then earth to the conduit - if that is acceptable?

Otherwise I suspect I would be looking at a total rewire, which I would prefer to avoid if possible.

As has been said before (I think) the continuity of the earthing through the metal conduit will possibly be broken - conduit coming adrift from junction boxes etc.
I had a similar situation on a job I did in a 60's conversion of a regency building a few years ago - we had to run new earth alongside the conduit, through it in some places.
It would have been easier just to rip it all out and start again - but not cheaper...

Mine is set into reinforced concrete - the conduit that is.

To run new cable everywhere would probably require surface mount conduit on the ceiling.

Which I am not totally opposed to mind you, but it's a fucker to get into the rooms as you have to get either through a 30cm thick concrete beam, or duck under it.

First attempt at skimming. Doesn't need to be perfect, because "you can hang your coats there"

Forest Hill, reckon it would be possible to pull new wires through?

I've cured the "fan staying on" issue- changing the wiring so that the switched live no longer shares a connection with the lighting circuit (and it's transformers) stops the problem.

Looks like the lighting SELV transformers, when not in use, are putting out a voltage that is high enough to trigger the fan.

I've now got a dual switch on the wall by the ensuite door, you can turn on just the light (2am visit) or light and fan.

Forest Hill, reckon it would be possible to pull new wires through?

This is what the sparks on my job did. But there were some places he couldn't draw through the existing conduit. If your conduit is held in place by the concrete and therefore hasn't come away from the junction boxes and if there are enough access points you might be alright.

I'll test the conduit, if I can- the ends are flared in the junction boxes, so would not pull out, but there may be breaks within the concrete.

I'd say that's unlikely, but I don't want to bet my life on that!

Are you getting certification for this work?

I'll get the whole thing inspected when I have a new consumer unit put in.

I'm not brave enough to fuck around with live mains, so I'll get a man in to deal with that.

Which does, in a way, annoy me as I've done everything else- but then I did get another bloke to fit the boiler that said.

Extractor is now signed off (by me) and I fitted the towel rad, so the ensuite just needs a mirror fitting and a lick of paint.

Also tallow the cables when running them through and it will be all new pretty colours so make notes how the colours run at the fuse box.

You are advising me to coat electrical cables in rendered animal fat?

Guess which of these are which:

^The original cabling.