Bathroom extractor fan replacement queries

[lowlevelowl]

Hi,

Me and my dad recently replaced a faulty extractor fan in the bathroom of the flat my girlfriend and I've owned for 4 years. In doing so we encountered a couple of issues that had us scratching our heads:

1) We couldn't locate an isolator switch for the fan (unless it was very well hidden up in the dropped ceiling of the bathroom). The only way we could work on the fan safely was to remove the breaker for the flat's lighting circuit. It was our understanding that for a bathroom with no natural lighting an isolator on a fan is a requirement?

2) The previous extractor fan was timed, connected to a permanent live, a switched live, and a neutral. The replacement extractor fan isn't timed and only requires a switched live and neutral. However, the previous owners of the flat had for some reason decided to fit a dimmer on the bathroom lights. We put the spare permanent live into a screw terminal, taped it up, and parked it where it can't contact any other wires, but this still leaves the fan running off a dimmer switch, meaning the fan speed ramps up and down according to the brightness of the lights. We never actually have the lights dimmed, they're either fully on or off, but it still doesn't feel quite right. Is this something I should look to get rectified i.e. fitting a timed fan, or replacing the dimmer with a regular switch? What might be the consequences if it's left as is?

Thanks in advance for any assistance!

 

[ban-all-sheds]

1) Not a requirement, unless the maker's instructions make it so, but good practice for the reason you've discovered. But then if you needed to work on the lighting circuit you'd have to do that in the dark too.

2) Consequences could be a damaged fan, a damaged dimmer, or both. You could put a timed fan in (probably should have one anyway in a windowless room), or get rid of the dimmer, as you only need a switch.

 

[EFLImpudence]

. It was our understanding that for a bathroom with no natural lighting an isolator on a fan is a requirement?

How do we work on the lighting.

Oft quoted nonsense. It is useful when the fan faults and allows the continued use of lights.

2) The previous extractor fan was timed, connected to a permanent live, a switched live, and a neutral. The replacement extractor fan isn't timed and only requires a switched live and neutral. However, the previous owners of the flat had for some reason decided to fit a dimmer on the bathroom lights. We put the spare permanent live into a screw terminal, taped it up, and parked it where it can't contact any other wires, but this still leaves the fan running off a dimmer switch, meaning the fan speed ramps up and down according to the brightness of the lights. We never actually have the lights dimmed, they're either fully on or off, but it still doesn't feel quite right. Is this something I should look to get rectified i.e. fitting a timed fan, or replacing the dimmer with a regular switch? What might be the consequences if it's left as is?

That's very interesting.
Only the very small trigger current going through the dimmer with a timer fan but now all of the running current.
I haven't come across that before.

It may wreck the dimmer depending on its rating.

 

[JohnW2]

That's very interesting. Only the very small trigger current going through the dimmer with a timer fan but now all of the running current. I haven't come across that before.

Yes, it is interesting but, like you, I've never come across it (hence had to think about it) before - I suppose because bathroom lights are very rarely on dimmers. However, it's logical enough - the trigger input is 'all or nothing' and often only actually requires a pretty low voltage to trigger but, with a non-timer fan, the fan is obviously 'dimmed', all the time, just as with the light!

Kind Regards, John

 

[lowlevelowl]

Thanks for the responses!

1) Not a requirement, unless the maker's instructions make it so, but good practice for the reason you've discovered.

Both the old and the new instructions specify a "double-pole fused spur" with a 3A fuse. Although the newer fan also says "when supplied from a 6A lighting circuit no local fuse is required", so I'm not sure which applies in our case?

It may wreck the dimmer depending on its rating.

Is this the rating of the dimmer or the fan (or both)? On inspecting the previous fan it was visually apparent that something on its controller PCB had blown which lead to the fan malfunctioning, but this was with it wired up correctly to both switched and permanent live. I don't know if this was just a natural occurrence due to the age of the fan, or a symptom of an issue elsewhere.

I'm not sure if we've actually improved the situation long-term as it stands, so will most likely look into replacing the dimmer entirely, as currently it's only used as a source of amusement when guests come round!

 

[JohnW2]

Both the old and the new instructions specify a "double-pole fused spur" with a 3A fuse. Although the newer fan also says "when supplied from a 6A lighting circuit no local fuse is required", so I'm not sure which applies in our case?

Interesting. When the new one says that you don't need a local fuse (i.e. a 'double-pole fused spur with a 3A fuse') when supplied from a 6A lighting circuit (the first one I've heard of being that sensible!) does it not say that, even those a local fuse is not required, an isolator is?

It may wreck the dimmer depending on its rating.

Is this the rating of the dimmer or the fan (or both)?

Both, really, but I doubt that the average bathroom fan would overload any dimmer.

On inspecting the previous fan it was visually apparent that something on its controller PCB had blown which lead to the fan malfunctioning, but this was with it wired up correctly to both switched and permanent live. I don't know if this was just a natural occurrence due to the age of the fan, or a symptom of an issue elsewhere.

That would be the timer module - non-timer fans don't usually (if ever) have any electronics or PCB. It's common for components in the timer modules to die 'of natural causes', and extremely unlikely that anything else caused it.

I'm not sure if we've actually improved the situation long-term as it stands, so will most likely look into replacing the dimmer entirely, as currently it's only used as a source of amusement when guests come round!

If you don't want/need the dimmer, just change it to an ordinary switch and all your 'troubles' will be over! (or, has been said, swap it for a tier fan, which might well be a better option)

Kind Regards, John

 

[lowlevelowl]

Interesting. When the new one says that you don't need a local fuse (i.e. a 'double-pole fused spur with a 3A fuse') when supplied from a 6A lighting circuit (the first one I've heard of being that sensible!) does it not say that, even those a local fuse is not required, an isolator is?

Yes, you're right, re-reading it I think the fuse is optional but the isolator is not. Given there wasn't one fitted for the previous fan should I look at getting one put in? Is it just a matter of convenience or are there safety implications as well?

If you don't want/need the dimmer, just change it to an ordinary switch and all your 'troubles' will be over! (or, has been said, swap it for a tier fan, which might well be a better option)

I think we will change out the dimmer as we really can't see a use for it. Is it safe to leave the permanent live parked inside the fan casing as described above, so that a timer fan is still an option in the future, or should this be disconnected somewhere at the switch?

Thanks again for all the advice!

 

[JohnW2]

Interesting. When the new one says that you don't need a local fuse (i.e. a 'double-pole fused spur with a 3A fuse') when supplied from a 6A lighting circuit (the first one I've heard of being that sensible!) does it not say that, even those a local fuse is not required, an isolator is?

Yes, you're right, re-reading it I think the fuse is optional but the isolator is not. Given there wasn't one fitted for the previous fan should I look at getting one put in? Is it just a matter of convenience or are there safety implications as well?

Strictly speaking, the regulations currently require you to follow manufacturer's instructions (although that requirement is going to be appreciably 'watered down' next year). There isn't really any significant safety issue - the 'convenience' advantage is that a fan isolator allows one to work on the fan without having to switch off the supply to the lights.

If you don't want/need the dimmer, just change it to an ordinary switch and all your 'troubles' will be over! (or, has been said, swap it for a tier fan, which might well be a better option)

I think we will change out the dimmer as we really can't see a use for it. Is it safe to leave the permanent live parked inside the fan casing as described above, so that a timer fan is still an option in the future, or should this be disconnected somewhere at the switch?

Yes, provided there is space (which there probably will be). You need to terminate the permanent live in a little bit of connector block, tucked safely away somewhere inside the fan casing. As you say, it could be needed in the future.

Kind Regards, John

 

[lowlevelowl]

That's great; thanks for putting my mind at rest.

 

[JohnW2]

That's great; thanks for putting my mind at rest.

You're welcome.

Kind Regards, John