But a 6 amp MCB is faster than a 5 amp fuse so will go first. Just another example of manufacturers instructions being wrong.
fuse for extractor fan
- Thread starter nick9one1
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Manufacturers instructions are wrong and there are no regs requiring isolators (as I have learnt to my peril 
).
But this message isn't getting out to consumers.
There is understandable confusion out there, which is why there are now products like this available:
To those who are playing safe, this could be a compromise worth having. Especially when we are used to the notion of warranties being voided if not following manufactures installation instructions!
).But this message isn't getting out to consumers.
There is understandable confusion out there, which is why there are now products like this available:
To those who are playing safe, this could be a compromise worth having. Especially when we are used to the notion of warranties being voided if not following manufactures installation instructions!
I can't be sure, but it looks as if that may well be a double-pole 'isolator' (with a fan logo) plus a fuse.Manufacturers instructions are wrong and there are no regs requiring isolators (as I have learnt to my peril
If that's the case, and if it's compliance with (silly) manufacturer's instructions that concerns you, then don't forget that many/most of the MIs call for triple-pole switches (and a fuse) for timer fans - so the product you've illustrated may well not be compliant with those MIs for such a fan
Kind Regards, John
I can't be sure, but it looks as if that may well be a double-pole 'isolator' (with a fan logo) plus a fuse.
If that's the case, and if it's compliance with (silly) manufacturer's instructions that concerns you, then don't forget that many/most of the MIs call for triple-pole switches (and a fuse) for timer fans - so the product you've illustrated may well not be compliant with those MIs for such a fan
Kind Regards, John
Tripple-pole!
https://www.cef.co.uk/catalogue/pro...e-pole-fan-isolator-switch-with-3a-fuse-white
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I fail to see how the lack of an isolator(a switch) can have any detrimental affect on a fan causing warranty problems.
That they might 'try it on' - like insurance companies - is a different matter.
That they might 'try it on' - like insurance companies - is a different matter.
a 6 amp MCB is potentially faster than a 5 amp fuse so usually will go first. Particular if a fault current was considerably higher than 5/6A, it may well be 'pot luck' as to which will go first.
Certainly silly, but 'wrong' depends upon what you mean. Having a 5A fuse and 6A MCB in series will not 'do any harm' or result in any danger.
Fair enoughTripple-pole!
That wouldn't make me any more inclined to install one. An isolator, perhaps, but never a fuse (on a lighting circuit).
Kind Regards, John
If someone was to blindly replace their 3 pole fan switch for a 3 pole switch with built-in 3amp fuse, the chances are they wouldn't ensure that the fuse actually protects both the permanent live AND switched live serving the fan.
I've never seen a fan's instructions ask for 5amp before.
I personally would be happy with a 6amp MCB.
I used to assume they only asked for 3amp because they thought people may connect it to a plug top - and that only 3 and 13amp fuses are the ones that seem to get recognised.
(Yes I did say plug top, that's what they call them in the electrical trade.)
I've never seen a fan's instructions ask for 5amp before.
I personally would be happy with a 6amp MCB.
I used to assume they only asked for 3amp because they thought people may connect it to a plug top - and that only 3 and 13amp fuses are the ones that seem to get recognised.
(Yes I did say plug top, that's what they call them in the electrical trade.)
Quite so - just like the concerns about 'warrany problems' if one cuts off a mouded plug and replaces it with something else.
That appears to be the problem - it appears that they not only 'might', but sometimes do, 'try it on'. The problem then is that, even for those of us who 'know better' (and a high proportion of consumers probably don't), it can be far too much of a hassle to fight one's way through arguments about warranties.
Kind Regards, John
It's certainly not something that I would even dream of doing, but I'm not sure how they could wire it that wouldn't protect both L and S/L?
Kind Regards, John
Assuming the wiring at the fan switch only consists of two 3 core+earth cables (feed in - perm L, sw L, N and load out to fan - perm L, sw L, N) I don't think you can connect a combined unit with 3 pole switch and fuse module so the fuse protects both lives.
How would you do it?
You did get me thinking - apparently before making the single faceplate version, Scolemore offered a modular system with two fuse holders!
I think they then decided fusing the switched live was superfluous (do modern fans use optoisolators?).
Some further research led straight back to here and déjà vu!:
https://www.diynot.com/diy/threads/extractor-fan-with-fused-isolator.523357/
In this case:
(Not my work!)
the switched live goes through the 270k resistor and a 15V zener before reaching the logic circuit. Theoretically, no need for a fuse
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Fusing only the perm live of the fan is surely no good, as the switched live to the fan would remain live if the fuse blew.
Having a fuse for perm live and sw live means only one fuse is likely to blow, leaving one live still, well, live.
I consider it bad practice for a fuse to blow and still leave part of the appliance live.
There was a rather complicated drawing here which did allow a fuse to serve both lives - the trouble was it meant the average householder would have good bit of rewiring to do, and the light switch had to be a double pole switch - which could mean an odd looking wall switch that may not match exactly with the rest of your house - if you like matching accessories. Also, a double pole switch, particularly if rated at 20amp, as they often are, can be a bit clunky/noisy.
Personally, I would prefer to wire the bathroom so a 3amp serves the bathroom light as well as the fan, meaning both lives in the fan WILL be protected by one fuse.
That said, I would be more than happy to say ignore the instructions (in this case) and don't have the 3amp fuse.
I think fan isolators are a good idea, as fans can jam up. Also hard to see when maintaining the fan without the light working.
Having a fuse for perm live and sw live means only one fuse is likely to blow, leaving one live still, well, live.
I consider it bad practice for a fuse to blow and still leave part of the appliance live.
There was a rather complicated drawing here which did allow a fuse to serve both lives - the trouble was it meant the average householder would have good bit of rewiring to do, and the light switch had to be a double pole switch - which could mean an odd looking wall switch that may not match exactly with the rest of your house - if you like matching accessories. Also, a double pole switch, particularly if rated at 20amp, as they often are, can be a bit clunky/noisy.
Personally, I would prefer to wire the bathroom so a 3amp serves the bathroom light as well as the fan, meaning both lives in the fan WILL be protected by one fuse.
That said, I would be more than happy to say ignore the instructions (in this case) and don't have the 3amp fuse.
I think fan isolators are a good idea, as fans can jam up. Also hard to see when maintaining the fan without the light working.
Yes, good point.
If you had removed the fuse, but didn't turn off the isolator, you may get a bit of a surprise from that terminal block.
When a fuse is removed, the assumption is the equipment is isolated.
And having two fuse holders doesn't help, as the switched live will never (probably never!) blow.
Unless I am missing something, to make sense, the switched live would have to originate after the fuse, as in the manufacturers diagram of post #3.
Which completely negates the need for a three pole isolator!
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