Wiring up a bathroom timer/humidistat fan - help!

[Lobster]

I've recently bought a humidistat/timer extractor fan for a bathroom, to replace a broken (non-humidistat) one (this model: ). However, although I've fitted plenty of these before, I'm really scratching my head over wiring this up. I have L, N, and switched L wires feeding it, so it will switch on with the bathroom lights and stay on for a bit, governed by the timer (and humidistat as needed). There's a terminal block inside the fan labelled L, N and LS, but the pre-connected wires don't make sense to me

- there's nothing at all connected to the LS terminal. Seems to me that it's been incorrectly factory-wired but looking at it I can't figure out how it ought to be, or whether I should send it back?

I've put a rubbish photo of the fitted fan here:

...and here's a corresponding sketch showing more clearly where the wires go (note there's a pull cord switch fitted which I'll want to over-ride anyway). Nothing on the circuit board saying which wires are which:

Manufacturer's wiring instructions, such as they are, are here (mine will be fig 4):

It's all a bit awkward because this is in a rented property, ie not my home; although my tenants are fine about me going round to sort it, I can't keep on pestering them indefinitely, and need to be able to just go back once more and resolve it for definite....

Any advice much appreciated

Thanks David

[Roger Mills]

It looks to me as if the terminal block is provided in order to cater for setups with or without an internal pull switch. The switched live obviously has to end up at the middle terminal on the circuit board, one way or another. As shown, it comes from the internal pull switch.

If you remove this switch and use your own external switching, you need to bring your external L, N and LS wires onto the terminal block, and the output from LS on the terminal block needs to go to the middle terminal (yellow wire) on the circuit board.

[Ronald Raygun]

It seems to me the thing is factory pre-wired as a standalone unit which does not make use of the switched live you are able to provide. The idea is you just wire in the L and N, then use the pull switch to fire it up. Either this switch is momentary action (as opposed to pull-to-switch-on and pull-again-to-switch-off) so that pulling it once will keep the fan on for a fixed amount of time, or else it will just stay on for a fixed time after you pull it again to switch off.

It seems clear that the black wire is neutral, both orange wires are unswitched live, and the pull switch then makes the yellow wire switched live, which goes straight to the circuit board. Therefore as far as the circuit board is concerned, the top terminal is neutral, the middle one switched live, and the bottom one unswitched live.

I think what you need to do is make the yellow wire go from the switch to the circuit board indirectly, via the LS terminal in the block, in exactly the same way as the orange wire already goes from the switch to the circuit board via the L terminal.

That done, the pull switch is able to *provide* a switched live output to feed your light if you so choose, or if you are already providing a switched live from an external switch, the fan unit can accept that as input. The same wiring will work both modes, the two switches are simply in parallel, i.e. the lamp (and fan) will come on when *either* of the switches is on, and will only go off when *both* switches are off.

There is a further operating mode you might like to go for. This involves rewiring it by leaving the yellow wire alone (going from switch to circuit board). You also leave alone the orange wire which goes from L to the circuit board. But the other orange wire should go from the switch to LS instead of from switch to L. This way, the pull switch will make the fan come on only when the switched live which you supply is live (i.e. when you have switched the light on). How it would work would depend on whether the switch is momentary action or pull-on-pull-off. If momentary, you need to tug the cord each time you want the fan to come on. If p-o-p-o, the pull switch will change modes between "fan always off" and "fan comes on with light".

[John Rumm]

Woa horse... what timer?

If you have a fan with timer overrun, then you need L, N, and LS. LS kicks it off when the light comes on, and the internal timer keeps it going for a user selectable delay after LS goes off using power from L.

With a humidistat fan there is usually no timer. You feed it L and N (and you can park your unneeded switched live in the LS terminal out of harms way). It comes on when the humidity reaches the trigger threshold, and goes off when sufficiently below it.

Now yours has a party trick with a dangly cord. Chances are all this does is manually turn the fan on, overriding the humidistat (handy for clearing the air when it ain't steam you are trying to shift!) This type of switch could be a toggle effect - changing back and forth between on or off each time you pull it like a light switch (a multimeter on ohms will soon tell you). The other alternative is the fan is posh enough to have a timer as well. In which case I would expect mr. dangly to be a pull to make switch that opens when you let go, and it will trigger the fan for a timed duration - again overriding the humidistat.

Hence, long and short: connect N to N, L to L, and LS to LS. Set the humidity setting so its not running all the time. Show the tenants the string to pull to get rid of whiffs, and possibly remind em to pull it again if it turns out there is no timer.

[Lobster]

Thanks very much for the responses: am happier now! and confident I can sort it out.

To follow up - it's certainly got an overrun timer in addition to the humidistat: has to have one, as this is an internal bathroom. There are two little dials within the gubbins of the fan; one to set the humidity and the other the time.

Also FYI - I'm definitely removing the pull-cord switch as it can't be used, as per the instructions (for reasons of geometry/bad design) if the fan is ceiling mounted, as mine is. Toolstation don't stock a humidistat fan without the pull cord.

Thanks again David

[John Rumm]

OK, without the pull cord you will lose the timer operation altogether with the wiring as it currently stands.

If you want to have both "fan on with the light", "overrun after", and "humidistat control", you will probably need to tweak the internal wiring.

Going by your circus diagram, you might get the functionality you need by disconnecting the yellow wire from the pull switch, and connecting it to the top of the LS terminal which was originally parking the LS wire from the light switch / ceiling rose. Hence turning the light on will be the same as pulling and holding the pull cord.

[Lobster]

All now sorted and working, thanks to all! David