Bathroom extractor fan without fuse

[Midwest]

Which pole of the TP isolator does the fuse protect, switch live or permanent live.

Its your choice

 

[Midwest]

The fuse is not required to protect the switched line from overload, however if the fuse blows and the fan stops and then someone is working on the fan they will be expecting that the fuse has removed power from the fan however the switched line would still be live and subject someone to the risk of shock.
Whilst you might say anyone with any sense will switch off the isolator, since these are domestic fans non professional persons are likely to be investigating and therefore may be subject to a shock risk.

I think you are thinking this too much

 

[Deleted member 26818]

Presumably the option is there to wire it as you require however I would expect that most people might wire it like this:

View attachment 34115

As this covers the most obvious arrangement that is identified on most fan installation instructions (assuming the TP isolator has a 3mm contact gap)

Looks like it is wired back to front.
Feed to the light switch should be taken from the unfused side of the fuse.

 

[Richard Burns]

Looks like it is wired back to front.
Feed to the light switch should be taken from the unfused side of the fuse.

That is really rather the whole point, to ensure the whole of the fan is fused down, not just one half of the supply.

 

[Deleted member 26818]

Yes, just don't like the light being fused with the fan.

 

[westward10]

Looks like it is wired back to front.
Feed to the light switch should be taken from the unfused side of the fuse.

Like I said before the switch is a half baked idea to solve a problem which isn't a problem in the first place.

 

[Midwest]

The same could said of the hallway & landing light switch. Should we not be wiring the ground floor & first floor lighting from the same mcb. If we use a non fused TP&N isolator, if a fan malfunctions, the same non professional person, could put his pinkies in there and get a shock. There's just no helping some people.

The use of a fused TP&N switch, in it's simplest form, allows the installer to 'take account of the manufactures instructions', by fusing the live supply to a fan. If that's what you want to do.

 

[westward10]

Agreed but it has been manufactured to fuse only one pole leaving the installer to figure out the rest. I guarantee these isolators have been fitted the conventional way leaving only one pole fused there is absolutely no doubt about it.

 

[Deleted member 9648]

Agreed but it has been manufactured to fuse only one pole leaving the installer to figure out the rest. I guarantee these isolators have been fitted the conventional way leaving only one pole fused there is absolutely no doubt about it.

My understanding is the 3a fuse is (laughably) intended to prevent the fan catching fire in the event of the motor seizing. As a timed fan will not operate without the permanent live it would seem to me that only fusing this pole and not the switched live would still achieve that (comical) aim.
Maybe the next amendment will require all fans to be constructed of non combustible material....ie sheet steel. Or the installer must construct a non combustible enclosure around the entire bathroom.

 

[westward10]

My understanding is the 3a fuse is (laughably) intended to prevent the fan catching fire in the event of the motor seizing. As a timed fan will not operate without the permanent live it would seem to me that only fusing this pole and not the switched live would still achieve that (comical) aim.
Maybe the next amendment will require all fans to be constructed of non combustible material....ie sheet steel. Or the installer must construct a non combustible enclosure around the entire bathroom.

There would be an argument the switched live will still be live if the fuse blows, not from me but I must agree with the 3A fuse being used to prevent fire, would it really blow if the fan locked before the windings heated the enclosure enough to catch fire. I thought these fans incorporated thermal fuses anyway.

 

[Toneyz]

The fan isolator/fuse unit should only be for the fan not the light as well I have not fitted one of these units yet but if Idid Iwould wire as a switch-fuse unit but with P/L from load side of switch link through fuse to P/L in fan.

 

[Pete999]

Correct me if I'm wrong the 3A fuse is as posted for overload protection the 3 pole switch for isolation. I think the fan is powered via live/line and neutral therfore fuse in perm.live the switch wire just triggers the timer and not powering the fan motor.

Correct a mundo

 

[Midwest]

Bored so spent some time looking for information about fuse size for fans. Note some manufactures state their fans most be protected by a suitable fuse, but not specifically what. Some did, Manrose 3amp for example.

Found this posted by 'rocknroll' on the IET forum in 2012;

'This is likely to happen for a few years to come I am afraid no matter what protective devices you use to protect the fans, I will now enlighten you on the matter, in 2011 whilst at Cambridge this issue was raised and the subject related to fire and forensics.

Firstly some incidental information before I get into the main subject, the fan catching fire.

In an earth fault condition the MCB tripped nine times out of ten compared to the 3 amp fuse.
In a short circuit condition it was around 50/50 MCB and fuse.

Now the fire bit, this normally happens in the stall mode, that is when the blades are impeded either because they are full of fluff, debris from the ceiling void, stuffing them with toilet paper to stop draughts or malicious acts.

During this prolonged stall mode the windings overheat and eventually ignite spreading to the plastic components such as the housing etc; many investigations have found the MCB and fuses intact after a fan fire incident, manufacturers are now required to insert a discrete about the size of a pin head into the windings, a thermal fuse, also the polymers used for the housing have been changed as well, various chloride and nitrogen compounds have been added at the extrusion stage so that the plastic chars rather than burns, but there are still fans being manufactured to the previous standards and with the many thousands of fans out there pre 2011 it is still likely to be a problem for some time to come, although some responsible manufacturers have taken this on board it will be a while before everybody plays ball'.

He gives no link or citation, (and not sure how Class 2 would have earth fault?). It would seem that bathroom extractor fans have caused quite a few fires, but exactly why, is never reported. One suggestion cites poor maintenance, i.e. not being de fluffed. Some report burning fab falling from ceiling onto carpet or plastic bath.

I note that reg 537.3.2.5 states a device used for mechanical maintenance, does not necessarily require interruption of the neutral conductor (TN supplies), so just a double pole FCU would suffice?

And it does seem that some fans have thermistor protection, Xpelair for example.

Anyways, hope you are all now suitably bored.

 

[westward10]

Confirms one thing the fuse is not foolproof when it comes to preventing fire.

 

[Wilko]

Confirms one thing the fuse is not foolproof when it comes to preventing fire.

Yes, so I don't understand why the fans that require fusing don't come with one from the factory? Then it could be the right fuse, if BS1362 3A isn't ...

 

[Midwest]

You'll have to ask the manufacturer about that, even the Xpelair fans with internal thermistor protection, require a 5amp fuse (maximum). Suspect with 'all' these fires, is a way of mitigating litigation for them.

I'm off to de-fluff my fan

 

[Wilko]

I'm off to de-fluff my fan

Yes, a warning sticker to be applied to the fans perhaps?

 

[haptism]

I cannot find any fans that dont require a fuse as per instructions, which would save all this faffing about !

 

[Wilko]

Hi - FWIW I've been having a little look and thought it might be of interest.
Imagine a fault occurs on the fan that causes a 10A fault current ... a manufacturer recommended BS1362 3A fuse will disconnect in about 6 sec and a BS6098 6A MCB will take about 600sec. So this could be significant, 2300W for 10 sec (say) vs 10 minutes (say).
Can I create a 10A fault in the fan? I volunteered the Venta Axia Silent in my bathroom to the cause. Running on high speed it draws about 0.04A as shown on my natty little clamp meter. When it's stalled it draws about 0.05A and emits a faint hum of protest (was only a little screwdriver after all). I left it stalled for a minute and no indication of current creeping up. But I admit my red wine inspired testing is hardly conclusive or ever likely to be. So I've written off to tech services and asked them. I can't wait

 

[haptism]

Not sure if you could replicate a fault that would draw exactly 10 amps (although you probably could if you had special equipment ect). I imagine if stalling it for one minute draws 0.05A then any fault current significantly higher than this would eventually burn the windings out, which could draw alot more than 10a, and so operate the protective device quickly. For what its worth, the fan I bought needed a 1amp fuse, which I put in the fused fan isolator on the switched live, no over run.