bathroom fan isolator advice

gasket · 1 Jan 2021

Hi all. I'm looking for a quick bit of advice if possible re: bathroom fan isolators.

I need to replace two extractor fans while replacing two bathrooms. The house was built around 1990 and the fans are the originals - which are now horrible, noisy and yellowing plastic.

The existing fans are simple, on-off types which are connected to dedicated lightswitches. They run off the upstairs lighting circuit.

I would much prefer to have fans on timers or have them humidity controlled.

So, I was delighted when I removed the covers on both fans and found an unused permanent live feed - in each case this has been left in a choc-block under the fan housing. So I have everything I need to fit the fan that I would like.

However, there is not currently an isolator - instead, to work on the fans it is necessary to switch off the MCB for the upstairs lights.

The lightswitch that controls the lights has a single length of Twin and Earth (blue, brown and green/yellow) running into the loft. The supply to the fan back down from the loft is a 4-core wire with red (perm live), blue, yellow (switched live) and earth. In the loft space above the bathroom there are a number of junction boxes which are all easily accessible. The walls are dot and dab plasterboard and the wires are free to move in this space (so I could drag new cable up and down if absolutely necessary).

Here are the pics:

So, here are the questions:

when fitting a new fan with a timer, into an existing circuit, is it necessary to add an isolator? (the bathroom does have an opening window - which I understand changes some requirements).
if it is necessary - then I see three places it could be fitted.
- the easiest place would be above the fan in the loft. This would simply be added in series to the final 4-core run going down to the fan. But I'm not sure if this is acceptable as you'd need to know it was there.
- The second easiest solution would be to put the isolator directly above the fan (this would be zone 3, well above the WC approx 2m from floor - as I could simply break into the plasterboard above, but don't fancy a pull switch and suspect a normal switch would be unacceptable.
- The most inconvenient thing to do would be to fit the switch on the wall outside the bathroom. This would mean bringing in an electrician as a replacement circuit would need to be run to take the perm. live from the switch location into the loft and over. It would be an incredibly easy job for them as that wall is just a stud and the cables can easily be pulled up into the loft, but I hadn't budgeted on paying someone to do this - so in this case I may have to just replace the fans like-for-like with simple on-off units.

Any advice would be very welcome. Thank you.

EFLImpudence · 1 Jan 2021

gasket said:
However, there is not currently an isolator - instead, to work on the fans it is necessary to switch off the MCB for the upstairs lights.

As it is to work on the lights.

1. When fitting a new fan with a timer, into an existing circuit, is it necessary to add an isolator? (the bathroom does have an opening window - which I understand changes some requirements).

It is not an electrical requirement but is a good idea. Window has no bearing on it..

Where you fit it outside zones 1 & 2 is up to you.

JohnD · 1 Jan 2021

you can fit it high up on the wall, next to the ceiling. If the cable comes through the ceiling, you can thread it into the backbox.

you will probably only need to isolate the fan every few years, when you clean out the dust, or every ten years, when you swap the fan for a new one, and in each case you will be standing on your stepladder (or the edge of the bath) so will be able to reach.

What is the height of your ceiling above the floor level? This may be relevant if the isolator will be above the bath or shower tray.

winston1 · 1 Jan 2021

gasket said:
So, here are the questions:

when fitting a new fan with a timer, into an existing circuit, is it necessary to add an isolator? (the bathroom does have an opening window - which I understand changes some requirements).

if it is necessary - then I see three places it could be fitted.

the easiest place would be above the fan in the loft. This would simply be added in series to the final 4-core run going down to the fan. But I'm not sure if this is acceptable as you'd need to know it was there.

The second easiest solution would be to put the isolator directly above the fan (this would be zone 3, well above the WC approx 2m from floor - as I could simply break into the plasterboard above, but don't fancy a pull switch and suspect a normal switch would be unacceptable.

The most inconvenient thing to do would be to fit the switch on the wall outside the bathroom. This would mean bringing in an electrician as a replacement circuit would need to be run to take the perm. live from the switch location into the loft and over. It would be an incredibly easy job for them as that wall is just a stud and the cables can easily be pulled up into the loft, but I hadn't budgeted on paying someone to do this - so in this case I may have to just replace the fans like-for-like with simple on-off units.

Any advice would be very welcome. Thank you.

1. No.
2. Not relevant as Q1 is a no.

However isolators are often fitted to save you switching off the MCB once every 10 years or so. One wonders why isolators are not fitted to every light for the same reason.

SUNRAY · 1 Jan 2021

EFLImpudence said:
As it is to work on the lights.

It is not an electrical requirement but is a good idea. Window has no bearing on it..

Where you fit it outside zones 1 & 2 is up to you.

Well as I read the regs the fan is only a requirement if there is no opening window or equivalent.

But as to your real question, no there is no BS7671 requirement to fit an isolator for a bathroom fan, however I wouldn't dream of not fitting one as I seem to work on several every year and it gets to be a real pain in the knees to constantly walk up and down the stairs, navigate the childrens toys laying around and catching the ironing board or vacuum cleaner pipe everytime I open the cupboard containing the awkwardly positioned consumer unit. It's so much easier to be able to have the bathroom light on when working on these devices too. My favourite place for the isolator is above the door outside the bathroom.

EFLImpudence · 2 Jan 2021

SUNRAY said:
Well as I read the regs the fan is only a requirement if there is no opening window or equivalent.

Not so - but not related to the OP's question.

gasket · 2 Jan 2021

Guys - thank you very much for such quick replies.

So, from the above it seems that there isn’t a requirement in the regs to install an isolator and the only downsides would be that I’d have to return to the breaker before working on the fan - and that I’d have to do it in daylight rather than use the bathroom light.

Now, usually where I’m advised that “it’s good practice to do something” I always adhere to this advice exactly. However - in this case I think I’ll rein my enthusiasm back a bit and will just fit the timer-fan without an isolator and will leave the rest of the circuit alone: the specific reason is that the consumer unit is just 8 feet from the bathroom and is easily reached being at chest height (so no great difficulty in flicking the breaker instead of the isolator) and also I’m fine using a headtorch and the good light from the window if I ever need to work on the fan.

So, for once - thanks to your advice it looks like I can take the easy option

you’ve saved me a job there, so thank you.

bernardgreen · 2 Jan 2021

gasket said:
So, from the above it seems that there isn’t a requirement in the regs to install an isolator and the only downsides would be that I’d have to return to the breaker before working on the fan - and that I’d have to do it in daylight rather than use the bathroom light.

Consider if ( when ) the fan becomes faulty and trips the protective devices for the lighting circuit/

It can be annoying and maybe dangerous to have no lights in the house until someone has isolated ( using a screwdriver ) the defective fan.

SUNRAY · 2 Jan 2021

EFLImpudence said:
Not so - but not related to the OP's question.

Why not so?

EFLImpudence · 2 Jan 2021

SUNRAY said:
Why not so?

Well, because:

SUNRAY said:
Well as I read the regs the fan is only a requirement if there is no opening window or equivalent.

is not the case.

SUNRAY · 2 Jan 2021

EFLImpudence said:
Well, because:

is not the case.

When did it change?
I helped add a wetroom last summer and LABC were totally happy with not having a fan, even commented on it when inspector saw the missing bricks and cable.

EFLImpudence · 2 Jan 2021

Twas ever thus, I think.

The window myth is just that.

SUNRAY · 2 Jan 2021

EFLImpudence said:
Twas ever thus, I think.

The window myth is just that.

Well it certainly didn't used to be a requirement in moons gone by and I quite clearly recall having to start fitting them in 70's in houses without windows in kitchen or bathroom. My heavily inspected building works in 1983-4 confirmed the operation of the window in a tick box.
I know not what's happend in the meantime until adding a downstairs toilet/shower room about 4 years ago for my daughter when she moved house, no mention on architechs plans no questions asked by BC.
And again last year already mentioned, Wet room on a disability grant and they inspected every minute detail including the flatness and pitch of the floor and even spread a measured amount of sand to measure the texture. Spring gauges to test the taps and toilet flush etc, I'm pretty sure something as distinct as a fan missing would be on the checklist.

EFLImpudence · 3 Jan 2021

Well, you seem to be verifying what I have said and showing that someone was mistaken in the 70s and 1983-4.

SUNRAY · 3 Jan 2021

EFLImpudence said:
Well, you seem to be verifying what I have said and showing that someone was mistaken in the 70s and 1983-4.

So when was the requirement for a fan introduded? as there were whole developement built in 70's without a single fan in site.

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bathroom fan isolator advice

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