Wiring a fan in a bathroom

[Dave40Llanfoist]

I am building an extension and would like to run the bathroom extractor fan off the 45A shower pull switch instead of the light switch. This is because to me it makes more sense to run the extractor when the shower is on, not when the light is on!

My question is how to do this, if I am feeding the extractor with 3core + earth to allow a timed overrun. I plan to insert a FCU after the shower switch, and a fan isolator switch to isolate all three poles. However, for my "unswitched" feed, do I tap a live off the 6A lighting circuit or do I take an unswitched feed from the 45A circuit, whihc must also be fused. I can see problems both ways: in the first option, if the fan was to join the live and switched live together it would be joining together two supply feeds; alternatively with two fused feeds off the 45A supply I'm putting two fuses in parallel.

Is there a more elegant solution?

 

[ban-all-sheds]

I am building an extension and would like to run the bathroom extractor fan off the 45A shower pull switch instead of the light switch. This is because to me it makes more sense to run the extractor when the shower is on, not when the light is on!

It made sense to me too.

I plan to insert a FCU after the shower switch,

So you'll immediately come to grief trying to get 2 x 10mm² conductors into the load terminals of the shower switch.

in the first option, if the fan was to join the live and switched live together it would be joining together two supply feeds;

It may or may not, but if it does you'd then have the nightmare scenario of the shower being supplied partly via the lighting circuit.

alternatively with two fused feeds off the 45A supply I'm putting two fuses in parallel.

And to add to the grief mentioned above you'd now be trying to get 2 x 10mm² conductors into the supply terminals of the shower switch.

And - to add a 3rd impossibility to the 2 you already have, you'd be trying to get 4 x 10mm² twin & earth cables into the switch pattress.

is there a more elegant solution?

Oh yes...

But there's also a solution even more elegant than that - put a flow-switch in the water supply to the shower.

 

[stem]

You've answered your own question really. Don't connect the fan to the shower circuit which should be exclusively for shower, not running other periphery.

In addition, you don't say what the size of the cable or MCB feeding your shower are, but FCU's are not designed for connection to 10mm cables fed by 45A MCB's

Instead wire your fan to the light circuit via a ceiling mount PIR sensor that detects occupancy. That way the fan will operate when the room is used for err....other functions......Such as having a bath. Also, there will be no worries about forgetting to switch it off.

 

[JohnD]

putting the fan on the light switch means it will continue running while you brush your teeth and cut your toenails. All the steam and water does not magically disappear the moment you turn off the shower. Wet towels also hold a lot of water.

 

[ban-all-sheds]

FCU's are not designed for connection to 10mm cables fed by 45A MCB's

If they'll take 2 x 6mm² they'll take 1 x 10mm²....

Instead wire your fan to the light circuit via a ceiling mount PIR sensor that detects occupancy. That way the fan will operate when the room is used for err....other functions......Such as having a bath.

And by going in there for the briefest time to wash your hands, clean your teeth, get something out of the cupboard, change the towels etc, none of which need the fan to come on while you are in there, let alone carry on running after you've left..

Also, there will be no worries about forgetting to switch it off.

I wouldn't claim that nobody in our house ever forgets, but it's not common.

putting the fan on the light switch means it will continue running while you brush your teeth and cut your toenails.

And it means it will come on when all you've gone in there for is to brush your teeth etc.

And it means that if you do need the fan you'll have to turn the light on even if it isn't dark.

All the steam and water does not magically disappear the moment you turn off the shower. Wet towels also hold a lot of water.

Which is why you have a timed overrun fan.

And/or a humidistat one.

 

[JohnD]

I have no objection to a 25W fan running for a few minutes every time someone uses the loo or washes their hands. Do you?

 

[ban-all-sheds]

It's not a few minutes though, is it, for an overrun fan....