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UK toilet extractor fan
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Gyro:

--- Quote from: SteveyG on August 20, 2021, 12:40:13 pm ---A 3A fuse will not prevent a fire however  :-// A 3A BS1362 will carry 6A indefinitely so over 1kW

Servicing doesn't require lighting from the existing electrical installation otherwise how would you service the lighting, or complete an installation before energised?  :o

--- End quote ---

I agree with you. I'm not arguing that it makes sense. Just that's the way it's currently done / written. I didn't bother following up the additional references in the video.

I suppose the onus is on the fan manufacturer to explain why they think a 3A fuse would make any difference to its safety.

The only thing I can possibly think of is that a fan might get wired in 0.5mm flex (there's no way you're ever going to squeeze solid 1mm or 1.5mm 3 core+CPC in there - certainly on a ducted one). This wouldn't be sufficiently protected by a B6 MCB under the regs though. Sorry, I'm grasping for explanations - not knowing what the fan instructions say about the size of cable, I can't say though.
themadhippy:
As usual Bigclive has already dissected one.
richard.cs:
Somewhere I have the reverse-engineered schematic of mine, from when I modified to trigger from a current transformer. Notable points:

* It's a resistive dropper not a capacitive one.
* The switched live goes straight into a high-value resistor, so there really is no need to worry about fusing on that input.
* It's a quad-NOR configured as an RC timer, with a very high resistor value and a modest electrolytic, maybe 220 uF.
* I seem to remember the capacitor is normally charged and discharges to start the time delay (which ends once refilled), this may be because keeping the electrolytic biased reduces leakage current which would otherwise affect timing.
* The whole board is neutral-referenced.
* A small triac in the neutral is used to switch the motor.
* I can't really remember but I think the board may have been given a negative supply relative to neutral, so as to allow negative gate drive for quadrant 2/3 operation and avoid quadrant 4.
Majorbob:

--- Quote from: SteveyG on August 20, 2021, 11:20:12 am ---
--- Quote from: Gyro on August 17, 2021, 06:24:22 pm ---Unfortunately, the IET wiring regs always defer to the manufacturer's instructions. If the manufacturer specifies a 3A fuse, then there must be a 3A fuse to meet the regs.

--- End quote ---

It's not quite phrased that way any more, since 18th edition it just says "shall take account of", meaning take note, but not necessarily follow. The wording was changed since so many import products had badly written or incorrect instructions.

A 3A BS1362 fuse will not offer any discrimination compared to a B6 MCB so it is not providing any electrical benefit, however if there is a warranty claim on the fan they may not offer the warranty if it is not installed according to their instructions.

An isolator for the fan is not a requirement either, since the MCB is noted as a suitable isolation device (Table 537.4)

--- End quote ---

So according to 18th edition I can ignore the manufacturers instructions?  Any repairs and maintenance can be done during the day with the whole circuit off.
Gyro:
'Ignore' sounds like a pretty extreme interpretation of 'take account of'. There are clearly going to be cases (a lot of Chinese manufactured light fitting for instance), where the installation instructions are going to be wrong for the UK - eg. Not including instructions for earthing metal fittings. Something like specifying a specific fuse rating are less open to interpretation.

What are you wiring the fan up with? will it directly accept standard 1.5mm2 PVC solid 3 core and earth? Edit: Ah, they do make it in 1mm2, I didn't think they did.


At the end of the day, I don't think anyone here is going to publicly tell you that you can ignore the manufacturer's instructions when personal safety, insurance etc. are involved.
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