How to use an extractor fan with a dimmer switch?

[Marvo]

Update....

I have fitted the fan. It works just fine with the dimmer. As long as the lights are are least half full strength when you initially switch it on then the fan comes on. You can then dim the lights as much as you want as the PL keeps the fan going.

I guess if you dimmed them below half, the fan would switch off after the overrun, but the boy always has the lights full on and I only dim them that low when I need a quick visit to the loo in the night. In fact, it works perfectly as I don't want the fan to come on in the middle of the night.

I probably wouldn't suggest it to a customer though.

If you have the dimmer on low and the fan doesn't start running then there's a good chance it's going to get hot very quickly. Most domestic fans motors are designed that their own internal impedance during a stall situation is high enough to keep the stall current (LRA) at a safe level and prevent thermal runaway that might lead to a fire, this is often referred to as 'impedance protected'. Most domestic fan motors should also have a thermal fuse on the motor windings to provide further protection against fire.

Problem is that if you're leaving any possibility of the fan being in a stall situation for any length of time you're relying on the fact the fan was well designed with good protection components which might be a bet I'd take with a good brand fan like an S&P or a Ziehl/EBM but probably not with a generic Chinese rebranded unit.