Bathroom Fan Wiring - is it compliant?

[rcd1976]

I've got a bathroom fan with a timer. The best place for a 3A isolating FCU is very near a ring main, but I'd like it to be controlled with the lightswitch, with a switch next to it offering over-ride of the fan.

This will work electrically:

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• rcd1976
• 25 Feb 2012
• 1

But is it ok with regs? Will they be ok with me putting a ring main in one pole, and the lighting circuit in another pole? I could power the fan off the lighting circuit but it'd be an extra, long, fiddly run of cable. Much easier this way.

Do you think this will get signed off by Building Control's electricians?[/img]

 

[RF Lighting]

Absoloutely not.

It's dangerous, and it'll trip your RCD(s) anyway.

 

[SpecialK]

Isolate the circuits using a relay powered by the light switch?
Not sure how it would trip the RCD, however I would think having a socket circuit running into a light switch would be a bad idea unless the light switch has a warning label on it.

 

[holmslaw]

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[holmslaw]

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[JohnW2]

No, its dangerous and unacceptable try this View media item 43181

What purpose does the 3-pole isolator serve, given that both its L ad S/L feeds derive from the same output of a dedicated DP FCU? I suspect you may say that it's to satisfy the fan's MIs to the letter (if the MIs call for a 3-pole isolator), but surely a DP switch which supplies both L and S/L is functionally the same as (and as good as) a 3-pole one?
In case it wasn't clear, I should perhaps have added that my thinking was that the switch of the DP FCU would provide the 'override' functionality that the OP wanted, which is why I presumed you had included the 3-pole switch/isolator for some other reason.

Kind Regards, John.
Edit: clarification added

 

[rcd1976]

No, its dangerous and unacceptable try this View media item 43181

What purpose does the 3-pole isolator serve, given that both its L ad S/L feeds derive from the same output of a dedicated DP FCU? I suspect you may say that it's to satisfy the fan's MIs to the letter (if the MIs call for a 3-pole isolator), but surely a DP switch which supplies both L and S/L is functionally the same as (and as good as) a 3-pole one?

Kind Regards, John.

Yes, the fan manufacturer's instructions were for a double pole FCU before the live and switched live divide. The FCU on the original diagram is intended to satisfy this.

Which regulation would my original design break? I can run it all through the lighting circuit but it's a real pain to cable.

Is there a separate problem with giving yourself a manual override of the fan's timer by putting the neutral on a single-pole switch as well? It's for an en suite and if you go for a pee in the middle of the night it'd be nice not to have to wait 15mins for the fan to shut off...

Don't understand why the original design would trip any RCDs. A double-pole switch is designed to switch live and neutral, so there surely isn't any leakage between poles...

Thanks for comments so far.

 

[JohnW2]

Yes, the fan manufacturer's instructions were for a double pole FCU before the live and switched live divide. The FCU on the original diagram is intended to satisfy this.

It sounds as if it does.

Which regulation would my original design break? I can run it all through the lighting circuit but it's a real pain to cable.

It is potentially dangerous to have two different circuits using the two poles of a DP switch, since it's an unusual/unexpected situation and would require two circuits to be isolated before one could safely work on the switch. At the very least, the regs would require a prominent notice to warn of the need to isolate two circuits before opening the switch - but, even then, it's not nice, and there might be more specific regs (can't think of any at present) which forbid it. A 'catch all' is that by using a DP switch (probably with terminals labelled 'L'and 'N') in that fashion you would almost certainly be working contrary to the Manufacturer's Instructions - which, in itself, is a violation of the Wiring Regs.

Is there a separate problem with giving yourself a manual override of the fan's timer by putting the neutral on a single-pole switch as well? It's for an en suite and if you go for a pee in the middle of the night it'd be nice not to have to wait 15mins for the fan to shut off...

I'm afraid that's a question which is going to get people saying that you don't know what you are talking about and shouldn't be contemplating doing this work. A SP switch in just a neutral is always very dangerous. Think about it ... the live may be switched on but, because of a separate switch in the neutral, the fan won't be operating, so someone could start working on the fan (e.g. to replace it) without realising that there were live connections to it. Indeed, they might even find your neutral switch and think that, because it stopped the fan working, it was safely isolating the fan from power.

Don't understand why the original design would trip any RCDs. A double-pole switch is designed to switch live and neutral, so there surely isn't any leakage between poles...

It wouldn't trip an RCD, for the reason you give - your design had no interconnection between the two circuits. I can but presume that RF had not looked carefully enough at the diagram when he suggested that.

Kind Regards, John.

 

[JohnW2]

It's for an en suite and if you go for a pee in the middle of the night it'd be nice not to have to wait 15mins for the fan to shut off...

It's occurred to me (and probably also you) that, with any of these arrangements, you would need to remember to switch the override switch back on, otherwise the fan will not work subsequently. With most (probably all) fans, you only have to remove the power momentarily to cancel the fan overrun, so (provided you didn't mind the fan coming on whilst you have the ensuite light on) you could switch it off, and then immediately back on, after you'd finished using the ensuite and turned the light off. In fact, provided the light is switched off, it's only the permanent live which needs to be switched off momentarily - so one option would be to use a SP 'push to break' push switch (a 2-way push switch, wired the appropraite way around) in the permanent live feed to the fan - you'd then just have to push it and release in order to 'cancel' the fan over-run.

Kind Regards, John.

 

[SpecialK]

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[rcd1976]

Thanks very much John, I see what you mean. I'm just thinking of safe operation, rather than maintenance.

I'll have to re-route it all off the lighting circuit. I was going to put the FCU down at knee height under a desk in the next room though, which is going to use a lot of cable.

Are there any rules about where the fan FCU has to go? How close, etcetera, although presumably you're not supposed to put it in the bathroom itself?

 

[JohnW2]

Thanks very much John, I see what you mean. I'm just thinking of safe operation, rather than maintenance.

Yes, it would be essentially safe in operation, but one (and, particularly, the regs) has to think about an installation being safe to work on, as well as use.

I'll have to re-route it all off the lighting circuit. I was going to put the FCU down at knee height under a desk in the next room though, which is going to use a lot of cable.

I obviously don't know exactly what your setup is, but where is this DP light switch? It provides access to the lighting circuit L, and also potentially to the corresponding N (which your diagram had passing through it), so can't the FCU be fed from there?

Are there any rules about where the fan FCU has to go? How close, etcetera, although presumably you're not supposed to put it in the bathroom itself?

I don't think it would matter too much where the switched FCU was, particularly when fed from a lighting circuit - but, as you say, not in the batthroom itself.

Kind Regards, John.

 

[rcd1976]

Ok, think I'm narrowing down my options.

One last question: can you have a switched FCU inside a cupboard (under a basin or inside housing for toilet cistern and macerator) inside a bathroom? That's the last easy option...
To answer yours:

I obviously don't know exactly what your setup is, but where is this DP light switch? It provides access to the lighting circuit L, and also potentially to the corresponding N (which your diagram had passing through it), so can't the FCU be fed from there?

The light switch will be at normal height outside the bathroom door. Trouble, I think, is that as fan has a timer, it needs both a permanent and a switched live. So as far as I can tell, FCU has to come before the switch.

A triple pole-switch would do for isolation, but it needs a 3A fuse, and I don't think you can get a triple pole-double fuse switch without resorting to some massive custom grid that would be a bit ugly on a domestic wall (and guess it's pretty clumsy electrically too).

Thanks very much indeed for all your help with this.

 

[rcd1976]

[deleted]

 

[JohnW2]

Ok, think I'm narrowing down my options. One last question: can you have a switched FCU inside a cupboard (under a basin or inside housing for toilet cistern and macerator) inside a bathroom? That's the last easy option...

If it is reasonably accessible and not at risk of getting wet, that'sprobably OK. I have the FCU for a macerator within it's housing. I wonder what others think?

The light switch will be at normal height outside the bathroom door. Trouble, I think, is that as fan has a timer, it needs both a permanent and a switched live. So as far as I can tell, FCU has to come before the switch.

Do you have a problem with having the FCU close to the light switch? If not, how about something like:

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• JohnW2
• 27 Feb 2012
• 1

You could either use the FCU as the fan over-run override, or else could add a separate switch (maybe a push to break switch) as indicated.

...without resorting to some massive custom grid that would be a bit ugly on a domestic wall (and guess it's pretty clumsy electrically too).

In fact, the above could all be done with a 4-unit grid in place of existing light switch - and I don't think that would look too bad at all (I have plenty of grid switches in my house).

Kind Regards, John.