One Vent Fan for two rooms? (Wiring)

[Peter Hemmings]

Hi,

I am just finishing an en-suite shower which is right next to my bathroom, that already has a high power in-line fan venting out of the roof. Rather than buy another fan and roof vent, I want to utilize the present fan with a "T" and two return flaps. ATM I have a double pole switch which operates the timed fan.

Do I have to have some special safety circuit to make this system compliant?

I have the present fan fed via the lighting circuit and thought putting another isolating switch would be illegal as I would have two feeds to the fan.

Thanks

[Lurch]

On Mon, 14 May 2007 21:52:09 +0100, Peter Hemmings mused:

We used to do this quite a lot. Each bathroom had a douple pole switch, one pole for the light and the other for the fan. The 2 poles used for the fan were just wired in parallel. All you need to ensure is that there is isolation in all live poles (phase and neutral) at the fan.

No real need for the backdraft shutters though as the fan is sucking from each vent. You only really need them if you have 2 fans seperately switched that can blow air past the tee into the other bathroom.

[Andrew Gabriel]

I cannot work out what circuit you have from the description, which makes it difficult to provide meaningful answers. Does the fan have permanent live, switched live, and neutral connections? Where does the double pole switch come in?

[Peter Hemmings]

Oops, sorry about that.

Yep, as far as I know it must have because it runs as a timer.

Where does the double pole switch come in?

I was told I had to have an isolator switch so I bought one and wired it in. I see what you mean and unfortunately it was some time ago and cannot remember what I did. I just followed the instructions!

Apologies to you all.

I think my actual question is, how do I need isolate a timed fan motor operating from two switches?

I assume I must be able to work on the fan without switching off the lighting circuit? I think the fan can be isolated by removing its connector though.

I will be investigating later this week and will come back with better information if I can't sort it out!

Thanks for your time

[Sparks]

You are going to need some more circuitry too, otherwise when you turn the light on in the bathroom, the light in the shower room will turn on if the switched lives are wired in parallel!

You could do it with a relay connected to each of the switch outputs of the two lights, to the coil of the relay. Then the Common of the relays connected to the permanent live of the fan (Which is also being fed directly from the lighting circuit), and the N/O terminals paralleled up and connected to the switched live input of the fan.

You would need to enclose it all in a suitably labeled box, in an accessible place, with the ability to isolate it all.

Sparks...

[Owain]

Then you need a *triple* pole fan isolator, not double.

Wot Lurch said, and here's some ASCII art, adapted from one I did a couple of years ago.

You have SWa in the bathroom and SWb in the en-suite. Both switches have

2 poles. (Both switches need to be fed from the same circuit.)

LIVE -------------- SWa Pole 1-----------LIGHTa-----------NEUTRAL | |-- SWa Pole 2----- | | | -----#--(timed) FAN--#--NEUTRAL | | | ----#--LIVE |-- SWb Pole 2----- | LIVE -------------- SWb Pole 1 ---------- LIGHTb----------NEUTRAL

Where shown # you need a triple pole isolator.

Using this, when either switch is on the shared fan gets electricity, as does the switch's own light, but the electricity can't run back through the other switch to the other light.

Owain

[Peter Hemmings]

Thanks for that, its better than i wanted!

What I had not made clear was that I was going to have separate vent pull-cords, but now I will do as above.

Can you just confirm I can install the 3 pole Isolator be in the loft next to the fan?

Thanks

[Andrew Gabriel]

It must be nearby the fan such that it's under the control of anyone working on the fan, or it must be lockable in the off position. So yes it should go in the loft.

[Peter Hemmings]

OK thanks for your info (and others), I am happier now!

Regards

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