Bathroom Fan Wiring

[Lincol]

I am replacing my bathroom fan which is currently wired from the lighting circuit via a 3 pole isolator and no extra fuses. The new fan suggests a 3A fuse which I intend fitting in the permanent live feed. This new fan will be wired with a switched feed from the bathroom light for the internal timer and what I would like to know, is it necessary also to fuse the switched feed at 3A otherwise it will be fused as the lighting circuit. ie. 6A MCB.
Thank you.

 

[EFLImpudence]

Oh, now you've started something.

It's actually not required to fuse the switched live but because the manufacturer shows both lines fused in the diagram this means you should or must.

You can get fans which do not demand fusing.

 

[sparkwright]

I would consider it bad practice to fuse both lives seperately.

The easiest way round this situation is to fit one fused spur (with a 3 amp fuse) that serves the whole of the bathroom (ie the bathroom light and the fan). Typically the fused spur would be outside the bathroom, above the door for example.

Anything else is complicated, and requires a double pole switch as a light switch, which can be awkward when trying to match existing accessories - especially a wall mounted switch outside the bathroom.

One theory on this 3 amp fuse business is that the manufacturer is simply worried someone is just going to wire it directly into a socket, or fit a plug on to it with a 13 amp fuse.

I think a lot of it is to cover themselves.

It's worth noting more than 99% of bathroom and toilet fans are wired to the lighting circuit without an additional 3 amp fuse.

However, I recommend you follow the manufacturers instructions.

 

[Lincol]

Like that Sparkright , that makes sense, then both lives are on 3A ( and the bathroom light which draws bugg... all , Not a lot !! ).
Cheers

 

[Lincol]

Sorry Sparkwright. Need my glasses !!

 

[JohnW2]

One theory on this 3 amp fuse business is that the manufacturer is simply worried someone is just going to wire it directly into a socket, or fit a plug on to it with a 13 amp fuse.

Maybe - but if the fan had adequate internal protection, there would be no problem with that, provided only that the cable used was man enough for whatever was protecting it.

I think a lot of it is to cover themselves.

We all say that, and it's probably true, but one can't help but wonder what they think they are 'covering themselves' against. A 3A fuse will allow best part of 5A (aka 1150W at 230V) to flow indefinitely and much higher currents than that to flow for appreciable periods of time - plenty to start a fire, if the the fan doesn't have adequate internal protection (which is what they really should be worrying about!).

It's worth noting more than 99% of bathroom and toilet fans are wired to the lighting circuit without an additional 3 amp fuse.

Indeed so - I have a lot of fans scattered around my house, and not one of them has a 3A fuse. However, as you say, I suppose the official advice has to be:

However, I recommend you follow the manufacturers instructions.

... and your suggestion of protecting the whole bathroom lighting circuit with a 3A FCU is, as you say, the simplest solution

No-one seems (yet!) to have mentioned RCDs

Kind Regards, John

 

[ban-all-sheds]

Anything else is complicated, and requires a double pole switch as a light switch

I was going to suggest that as a good way....

Gets rid of the 3P isolator too.

 

[ban-all-sheds]

No-one seems (yet!) to have mentioned RCDs

Troublemaker.

 

[JohnW2]

Anything else is complicated, and requires a double pole switch as a light switch

I was going to suggest that as a good way.... .... Gets rid of the 3P isolator too.

Do you mean ....

Untitled

• JohnW2
• 4 Apr 2015
• 1

.. if so, I think that probably the only sense in which it is 'better' is that it enables the fan to be isolated without also isolating (i.e. not being able to use!) the light - which I think is a pretty marginal advantage. That apart, if one simply runs the light off the same pole of the pull switch (which can then be SP) as the fan, then one ends up with sparkwright's suggestion...

Untitled

• JohnW2
• 4 Apr 2015
• 1

Kind Regards, John

 

[hawk84]

Hi, I had the same problem. I got around this by using a split patress mounted at high level outside the bathroom which contained a fsu and 3 pole fan isolator.
I have attached a drawing of what I did.

 

[Jackrae]

Fuses in supply lines are there to protect the cable, not the device supplied. Manufacturer is simply covering their behind by showing a fuse. As has already been stated, a 3 amp fuse will happily permit in excess of 1kW for a reasonable period of time, more than enough time for the fan to self ignite if it develops an internal fault. Decent quality fans have thermal 'fuse's built into their windings.

 

[endecotp]

I had a similar problem, and did consider replacing the current 6A MCB on this lighting circuit with a 3A one; since most of the lights are LEDs now it would be more than sufficient.

"Following the manufacturers instructions", in my case, would mean fitting a 3A "double pole fuse", i.e. a fuse in the neutral! No, I'm not going to do that!

 

[ban-all-sheds]

Really?

The MIs actually tell you to put a fuse in the N?

Can you provide a link to, or a scan of, those instructions?

 

[riveralt]

Hi, I had the same problem. I got around this by using a split patress mounted at high level outside the bathroom which contained a fsu and 3 pole fan isolator.
I have attached a drawing of what I did.

One hopes the OP has not been waiting three months for the arrival of your drawing.

 

[endecotp]

Really?

The MIs actually tell you to put a fuse in the N?

Can you provide a link to, or a scan of, those instructions?

http://www.anda.co.uk/sites/default/files/pdfs/077548 APL Mixflow fans 06-12.pdf

Scroll to the end. The schematic says "3 amp double pole fuse" above a box. I'd be interested to hear what you would think that box were depicting if it didn't have those words written above it.

This was an unbranded fan from Toolstation; it seems very similar to some Manrose fans I've seen pictures of. I found that PDF by googling the part number; I don't know whose website that is.