Bathroom extractor fan electrics

[Adam-the-Kiwi]

Another question for your collective wisdom, I'm afraid.

I'm replacing a slighty pathetic 4" shed extractor fan, mounted in the bathroom ceiling, with an inline Manrose 150mm fan (SF150S) which will be mounted in the loft and will probably vent directly out through the roof. The existing fan was wired directly to the light, no delay, with a short length of lighting flex directly from the light itself. We're planning on putting in a humidistat

into the bathroom to control the fan's operation. My plan was to wire it up thus:

- Put a junction box into the lighting circuit in the loft

- Run a spur, using lighting flex, to an isolator, (such as

,mounted outside bathroom

- Run lighting flex from isolator to the humidistat (only live core connected) and from humidistat to fan to provide switched live feed to fan

- Run lighting flex from isolator to fan for permanent live and neutral feed

Does this sound sensible? Are there any flaws?

One last question: the contacts within the humidistat are flat copper tabs with a small (~3mm) hole. What is the best way to connect the cable to these?

Cheers - Adam...

[David Hansen]

On 21 Feb 2006 08:28:09 -0800 someone who may be "Adam-the-Kiwi" wrote this:-

Sounds good.

Don't use flex, use cable.

Does the fan need a permanent live supply? Surely the fan just needs to come on when the humidistat calls for ventilation and off when the humidity is lowered? If that is the case then I would treat the humidistat just like a light switch and put a double pole isolator by the fan (out of reach of the bath or shower in the appropriate zone).

Ask the manufacturer.

[Adam-the-Kiwi]

David, thanks for the reply.

This was the main thing I wanted to confirm: that it's appropriate to run a spur from the lighting circuit.

Sorry, my misuse of terms.

The fan has connections for a permanent live and a switched live. I did consider wiring it exactly as you said but thought I might as well follow the manufacturer's instructions.

WRT the isolator: the one I've found is a 3-pole, but I can't see if it's rated for bathroom zones, which is why I was planning to put it outside the bathroom.

Thanks for the advice - Adam...

[David Hansen]

On 21 Feb 2006 09:32:40 -0800 someone who may be "Adam-the-Kiwi" wrote this:-

Does it have a timer? I cannot think of any other reason to have a permanent live supply to such an item of equipment. If it does have a timer do you want to use it? If the answer to both questions is yes then use a three pole isolator. Otherwise use a two pole isolator.

Zones are essentially a more complicated way of doing the same as the old bathroom regulations. It is perfectly acceptable to put an ordinary switch in a bathroom, provided that it is far enough away that one cannot stand in a bath or shower and operate it. Fan isolators should be beside the fan. If the fan is in a bathroom then the fan is likely to be high up and the isolator should be beside it, both outside the reach of someone in a bath or shower. In your particular case the isolator should be in the loft.

If the fan is not being controlled from the lights then another alternative is to supply it from a ring main, via a switched fused connection unit. However, this is usually more trouble as ring main wiring tends not to be in the loft, except in bungalows with solid floors.

[Harry Bloomfield]

Adam-the-Kiwi explained on 21/02/2006 :

A humidistat combined with a PIR/timer would be much better.

[Owain]

1/4 inch blades? These are the females which crimp onto the cable - you would also need the covers.

[Adam-the-Kiwi]

Yes, it does have a timer and no, I don't plan to make use of it. I'll look at a two pole isolator and presumably I need to connect permanent live to switched live.

Right, thank you. That makes the wiring much easier, anyway.

That's pretty much what I thought. I do have a mains feed into the loft (well, the cable, at least) - it was the supply for the old electric shower (would obviously need a new MCB), but I figured at the power rating of the fan (25W) it was perfectly OK in the light circuit.

Thanks again, David, for clear and uncomplicated advice.

Adam...

[Adam-the-Kiwi]

The fan does have a timer built it - but why both? I figured that the humidistat would obsolete the timer...

Adam.

[Richard Conway]

Possibly, although I wish ours had a timer as well as a humidistat as it often turns off a short while after getting out of the shower and then turns back on again half a minute later (assumedly a bit more steam from within the room rises and hits the sensor) it can even do this twice if I run lots of hot water when shaving afterwards. If it had a timer set to two or three minutes then it would avoid this and stay on constantly until all the moisture clears.

[John Stumbles]

If you could scroung a cheap timer module out of a timer fan you could wire that to be kicked in by the humidistat.

[David Hansen]

On 22 Feb 2006 01:23:09 -0800 someone who may be "Adam-the-Kiwi" wrote this:-

This should be covered in the instructions. However, I would start off by not connecting anything to the permanent live connection. Then the fan should go on and off as the switched live is energised. If that doesn't work time for another think.

[Harry Bloomfield]

Adam-the-Kiwi presented the following explanation :

The PIR obviates the need for the fan to be triggered by turning on the light. Someone walks in and the fans runs to not only clear the moisture, but the smells too. If someone uses the bath or shower it will continue to run until the room is cleared of moisture.

The above is also much easier to wire, just needing a LNE.

You can even buy fans with the above sensors built into the fans case.