Extractor Fan Isolation

Olivias Grumpy · 3 Jun 2019

Hi
Probably been asked before somewhere
I have a house built 1972
Downstairs loo under the stairs had a large extractor fan set on an angled concrete block with an internal duct cast into party wall terminating on the roof.
I’ve removed the block and intend fitting a flush fan. The cable connection presently is via a flex outlet about 200mm from ceiling.

I was going to replace the outlet with a fan isolator but can’t find one with a flex outlet
Is there such an item?
I could fabricate a spacer with a surface mount plastic switch box.
I could chase out the wall and bury the cable before the decorators arrive.
But know I’m told I can’t fit a fan switch in the room. Is this correct?
There is a wall mounted light switch in the room already.

Or am I stuck with a flex outlet even though a fan switch is safer?
Thanks

EFLImpudence · 3 Jun 2019

Olivias Grumpy said:
But know I’m told I can’t fit a fan switch in the room. Is this correct?

No.

Or am I stuck with a flex outlet even though a fan switch is safer?

No, your not stuck with a flex outlet.
You may have the fan switch if you want.

I don't know if there are any with flex outlet; the thicker ones might have a cut-out.

Much nicer with the cable buried although that will raise RCD questions.

SFK · 3 Jun 2019

I presume that the fan stops imediatly that the light goes out.
And that this plate will not be in Zone 1 or Zone 2 (EDITED>> which as in this case it is an Undertstairs loo is okay as there is no Zone 1 or 2).
Then this (and many others) will work:
https://www.screwfix.com/p/mk-13a-dp-switched-fused-connection-unit-with-flex-outlet-white/13479

Olivias Grumpy · 3 Jun 2019

Hi thanks for reply SFK
No original and replacement fan have timers. So I need 3 pole isolation

EFLImpudence · 3 Jun 2019

There are no zones. It's an understairs loo.

SFK · 3 Jun 2019

EFL, Good point, missed that. Edited now. SFK

Olivias Grumpy · 3 Jun 2019

EFLImpudence said:
There are no zones. It's an understairs loo.

Thanks for earlier reply.
I agree it will look neater if buried
It’s only about 150mm at right angle to existing flex outlet

Not sure what you mean about RCD issues?
Room has a small hand basin, does that make a difference to Zone?
Cheers

EFLImpudence · 3 Jun 2019

Newly conceled cables should have an RCD on the circuit. There might be one in the consumer unit already.

No, basins make no difference.

Olivias Grumpy · 3 Jun 2019

Thanks again
There isn’t a RCD on the fuseboard.
There are RCBO on the ring main, cooker and an outside garden socket

Didn’t fit anything on lighting circuits as I get fed up of nuisance trips when a bulb fails

winston1 · 3 Jun 2019

Olivias Grumpy said:
Thanks again
There isn’t a RCD on the fuseboard.
There are RCBO on the ring main, cooker and an outside garden socket

Didn’t fit anything on lighting circuits as I get fed up of nuisance trips when a bulb fails

An RCBO (well the RCD part of it) won't trip when a bulb fails as a bulb does not have an earth connection to leak to.

Olivias Grumpy · 4 Jun 2019

Perhaps I explained it badly
In another house I had with an RCD protecting the fuses, every time bulb failed, the lighting breaker tripped and likewise the RCD
So I individually protected the 3 circuits with rcbo and just rely on the 6a breaker for the lighting
Then if 1 lighting circuit trips I’ve still got the other for a certain amount of light to rectify the issue

Hope it makes sense?

winston1 · 4 Jun 2019

An RCD does not protect the fuses. It protects against unbalanced currents. It should not trip if a bulb fails for the reason I stated.

bernardgreen · 4 Jun 2019

winston1 said:
won't trip when a bulb fails as a bulb does not have an earth connection to leak to.

winston1 said:
It should not trip if a bulb fails for the reason I stated.

But RCDs do sometimes trip when a build fails. Hence there has to be a reason that you have not stated.

A likely reason for an RCD to trip is capacitive coupling of the CPC ( earth connection ) to the Live and Neutrals throughout the installation and the extreme high currents on the Live and Neutral while the failed lamp has a plasma discharge between Live and Neutral. Current capacitively coupled to the CPC can be such that imbalance on Live and Neutral exceeds the RCD trip threshold

Capacitive coupling includes stray capacitance between conductors in cable and the capacitors fitted in filters in equipment.

A plasma discharge in a failed lamp is effectively a short circuit ,zero ohms, between Live and Neutral through vapourised metal producing a fault current of hundreds of amps

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Extractor Fan Isolation

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