Can I use the shower switch to feed the switched live on the bathroom fan?

[me]

The "standard" circuit for a bathroom fan seems to be to operate it from the light switch which means it's generally only going to be activated at night. That seems odd to me. So instead can I take the switched live from the shower mains pull switch and feed that to the switched live on the bathroom fan so that the fan comes on when the shower is used, day or night? Seems like the logical way to do it but I recall some regulation not allowing the fan to be operated from the shower switch. Any advice please?

[Brian Gaff]

So you might want to operate the fan in there without the shower running, surely? I'm surprised no enterprising person has not created a relay control system to allow this by now, maybe they have. I have a bath more than a shower, and I don't have a fan, but if I want one it will have to be operated separately, and this would not be unusual. Brian

[Fredxx]

Many bathrooms have limited light. I suspect most baths are taken at night.

Why not get one with a humidistat?

[Theo]

Surely it has both a constant live and a switched live for the switch? That means the fan is triggered when the light is turned on, and powered from the constant live to allow the run-on timer to operate after the light is turned off. That's why it's powered from the lighting circuit rather than sockets or something else.

(also that lighting cables are already in or near the ceiling)

The shower pull switch is an isolator, it isn't intended to break current to the shower. It's primarily there for isolating the shower to work on it, or for safety shutoff in case of a fault. Typically people don't use it to control their showers, they have buttons or knobs on the front for that.

So it would be odd if the fan ran all the time the shower wasn't isolated. And if you isolate at the end of a shower, the run-on timer wouldn't operate

- precisely the time the bathroom is full of steam that you want clearing.

Sounds like a bodge to me. A humidistat would be the normal way to acheive this.

Theo

[ARW]

You cannot just remove the switched live from the lighting circuit to the fan and add a new switched live to the fan from the shower circuit.

Well you can but it will be an electrical bodge for quite a few reasons.

The first thing to consider is seeing if you can change the setup to a

2g light switch (or 2 pull cords) so that you can switch the fan independently to the lights.

I have done a few installs where the shower pull switch is used to also turn on lights, a fan and supply power to the shower. This has required a small CU in the loft is is a lot harder work than just having a separate switch for the fan.

[me]

Thanks for the replies. It occurred to me that maybe I'm overthinking this. (I should have mentioned) the fan has its own pull switch to turn it on and off so I can just turn it on myself when I have a shower. I think I got confused because I seem to remember that the fan has to be run from the light switch as part of the regulations. Is that right or wrong?

[Vir Campestris]

And? He's talking about linking it to a shower.

Many people have showers in the morning.

We have a humidistat on the fan in our bathroom. It doesn't come on as soon as I'd like reliably - seems to be weather dependent - and in any case that doesn't deal with smells.

Andy

[Fredxx]

Fit a thermal switch to the outflow?

A passive IR switch can reliably pickup people having a dump. Unless they sit on the throne for a long time to read a book.

[Rod Speed]

Even when they do. I could never fool my dad's internal alarm movement sensor by keeping still when reading a book in the main room.