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So I have a replacement bathroom fan that says to use a 3 amp isolator. Fine, no problem except all fan isolator switches seem to be 10 amp. What am I missing here?
What am I missing here?
7 amps
Happy to help! 🙂
I wouldn't be missing them, I'd have 7 too many. 😉
I would guess that a "3 Amp isolator" would be rated to a maximum load of 3A. The 10A isolator will handle up to 10A and your 3A fan is less than 10.
I looked at another fan and that was 3 amp as well......
You could then, presumably, run three of those fans through the one isolator.
(I Am Not An Electrician)
Thanks Cougar. Yeah, I get that but what I mean is why do bathroom fans seem to be 3 amp max when all the fan isolator switches seem to be 10 amp.
Basically, can I use the 10 amp switch with the 3 amp fan without blowing up the world?
I'd have thought if the fans required a 3 amp fuse then you'd be able to buy 3 amp isolators?
I have another isolator switch with a replaceable fuse but that's not three pole which is needed for the permanent live and switched live.
Does the installation manual call for a 3A fuse?
For example, the MF100T (beloved of STW) says:
"A double pole fused spur having contact separation of at least 3mm in all poles must be used and fitted with a 3A fuse"
Are you switching or fusing your fan?
A switch with a maximum current of 10amps means just that. It can switch up to that amount, but less is fine. Like your 13A plug socket in the kitchen can take a kettle at 10 amps, but you can also plug in your mobile phone to charge at 0.5amps.
The fuse is a different matter, it is there to protect the circuit and should be rated as per the instructions, like tomparkin says.
Yes Tom, exactly that. Think I've resolved it in my head now.
What I was trying to avoid was having the light/fan switch after the isolator as being able to isolate the fan but still use the lights would be handy. That was the route with the 3 pole isolator but looks like the only way to comply with the 3 amp requirement is to use a 2 pole fuse spur then run the switched live after. 🙁
You could then, presumably, run three of those fans through the one isolator.
3.333333333333333 actually.
You're welcome.
That means it needs an isolator switch rated to at least 3amps i.e. it can handle that level of sustained current.
A 10amp one will be fine as it is more than 3amps.
An isolator is not a fuse by the way.
You should be able to find a fused isolator (either 2 or 3 pole) - just fit 3A fuse.
E.g:
Edit
To clarify: the fan spec means that its supply must be fused at 3 amps. The isolator ratings are just the highest current it can be used for. You will need to fit a fuse for the fan supply as your lighting circuit is almost certainly fused at more than 3A.
But a fused spur with a switch can be used to isolate right? So you don't need a separate isolator switch?
You're fine to use a 10A isolator with a fan requiring a 3A one. The isolator is capable of switching up to 10A. You can replace the fuse in the isolator with a 3A fuse if you wish. (I'm not an electrician either.)
What I was trying to avoid was having the light/fan switch after the isolator as being able to isolate the fan but still use the lights would be handy. That was the route with the 3 pole isolator but looks like the only way to comply with the 3 amp requirement is to use a 2 pole fuse spur then run the switched live after. 🙁
It's a bit of a mess isn't it?
This thread is maybe insightful:
https://www.diynot.com/diy/threads/extractor-fan-with-fused-isolator.523357/
I don't think I've ever seen an isolator AND an FCU for a fan, but it almost looks like that's what you'd need to do to comply with the regulations.
I am not an electrician though.
You should be able to find a fused isolator (either 2 or 3 pole) – just fit 3A fuse.
What is the fuse protecting there though? The permanent live or switched live?
You should be able to find a fused isolator (either 2 or 3 pole) – just fit 3A fuse.
I've only looked at screw fix so far but none of the 3 pole have replaceable fuses.
I’ve only looked at screw fix so far but none of the 3 pole have replaceable fuses.
Have added link above. I don’t know if the same is available from screwfix.
What is the fuse protecting there though?
Probably the permanent live, but follow wiring diagram that comes with the fan.
Presumably you fuse the fan, but the light circuit is already fused.
To be blunt, I think you need an electrician.
I wouldn't. Are you not familiar with the meaning of the word "isolated"? 😉You could then, presumably, run three of those fans through the one isolator.
(I am also not an electrician)
It’s a bit of a mess isn’t it?
This thread is maybe insightful:
https://www.diynot.com/diy/threads/extractor-fan-with-fused-isolator.523357/I don’t think I’ve ever seen an isolator AND an FCU for a fan, but it almost looks like that’s what you’d need to do to comply with the regulations.
I am not an electrician though.
Thanks for this Tom, the linked thread is basically exactly what I'm asking and the responses interesting. Looks like it actually needs both to comply with the manufacturers instructions/regs although it's strongly hinted that the fuse shouldn't be necessary.
It all looks a bit daft, doesn't it, especially since the fuse is supposed to protect the wiring, and the wiring's going to be 1 or 1.5mm, and will be (probably) protected by an RCU at your consumer unit 😐
Am following along with interest though, as new extractor fans are on my TODO list in the near-ish future.
The internal parts of the fan may only be suitable to carry 3A. No point designing it to carry more. If you relied on the fuse/MCB at the consumer unit, which could be 10A (or much more depending which circuit it it connected to) then the fan would be overloaded in the case of a fault.
The fan should be locally fused similar to any other appliance (which would have a fused plug).
99% of bathroom fans should have a 3amp fuse fitted as the internal wiring is not capable of carrying any more than that. My old Niceic assessor used to love to tell me that, but not why you didn’t need two, one for the perm live and one for the switched.
The brand click do a fuse module and a separate 3 pole isolator that goes into a single faceplate which is my preferred method when installing
but not why you didn’t need two, one for the perm live and one for the switched.
My understanding of the internal wiring of timer fans is that the s/l just starts the overrun timer when the light is turned off, but it's the p/l that actually feeds the fan. Therefore the fuse should be on the p/l, however the Scolmore unit linked to above will solve the dilemma (although it's ugly as sin)
The entire point of a fuse is for it to be the weakest link in the chain. If the cuircet is to fail it fails in know place in a known way. All other wiring will be specified for >3amp. There should be fuse inline at 3 amps. How you do that depends can vary.
That scolmore/click isolator is what I use. My point being that the fuse in it would protect the permanent live into the fan but if it blows you can still put 6/10A into the fan wiring whenever you switch the light on. Anyway that’s enough of me moaning about half arsed electrical crap😂 buy one of them and it’s about as good as you can do to comply with manufacturers instructions
Get an electrician I think.
Please.
What you have told me is enough to tell me it would be a wise investment.
I'd pretty much come to that conclusion igm but still worth getting my head around just so it doesn't annoy me!
Looks like the options are the Click switch above or the 3 amp fuse (boxed and mounted in the loft) fitted in the circuit before the lights, fan or switch, then the isolator fitted above the door. Providing the low power spot lights are happy at 3 amps.....