Extractor fan, three pole isolator, fcu

[Grenage]

Thanks to the great advice I was given in other threads, I'm nearly done installing an extractor fan - ceiling through loft and fascia. Unfortunately I didn't check the manufacturers installation requirements prior to stating (oops), and they specify a 3a fuse.

Obviously as they state it as a requirement in the documentation, I've got to fit one; I appreciate that in reality I may not need it.

Would a 2 gang back box with a 3a fcu and a three pole isolator be acceptable?

 

[sparkwright]

The problem here is how do you fit one 3 amp fuse that will cover both the permanent live and the switched live of the fan?

One solution is to fit a 3 amp fused spur which serves the whole of the bathroom, ie a 3 amp fuse serving the bathroom light as well as the fan.

Alternatively, there is a rather complicated wiring diagram someone here will probably find for you that will show a 3 amp fuse serving just the fan, but I'm yet to see such a set up in real life.

In the real world, I would say the fans are either wired as indicated in my second paragraph; or, as often seems to be the case, the fans are simply wired to a 6 amp circuit without a 3 amp fuse.

Of course, one should always adhere to the manufacturer's instructions.

 

[EFLImpudence]

 

[Grenage]

Hi guys,

Thank you for your replies, that does clear things up - especially the diagram. While I do already have a DP pull switch in place, is there any reason one couldn't just wire the bathroom light's L and the fan's SL from the single fused live?

 

[EFLImpudence]

The whole point of this arrangement is so that the light is not controlled by the SFCU - which you don't need or really want - as it is to be able to isolate the fan should it become faulty.

 

[Grenage]

Good point!

Well it'll add more complexity (relatively), but it seems to be the way to go. Our consumer unit is old as hell, and the manufacturer states a fuse, so a fuse it must be!

Thank you for your help; much appreciated.

 

[Grenage]

As an afterthought, I assume one can't use one FCU for the live and one FCU for the switched live - with a three-pole isolator in a three-gang box?

Only reason I could think of is that it would mean there could be a max draw of 6A across both lines, rather than three across both. I suppose I answered that one myself...

 

[EFLImpudence]

As an afterthought, I assume one can't use one FCU for the live and one FCU for the switched live - with a three-pole isolator in a three-gang box?

Well, you could - but you don't need a 3P isolator because the FCU (or FCUs) do the job.

However, it could be considered unacceptable because of the two points required to isolate - and a bit naff.

Also, it is not really an advantage because the wiring would be no easier.

 

[Grenage]

I suppose so, I just thought it might be a bit neater, having that all in one box next to the fan.

 

[EFLImpudence]

I suppose so, I just thought it might be a bit neater, having that all in one box next to the fan.

It's usual to place the SFCU (and/or 3P isolator) outside the bathroom high near the door.
This tends to be relatively near the switch.

 

[Grenage]

I thought that sparkies preferred having then near the unit they were isolating, so they could be sure some plonka couldn't flip it without them knowing? I don't really care where it goes, but a switch in the loft is one less on the wall/ceiling.

 

[EFLImpudence]

We don't always get what we want.

It may not be allowed next to the fan - depending on the fan's position in the bathroom.

In the loft is fine as long as you can access it easily and it is identified.

 

[Grenage]

Aye, the fan is in-line and mounted in the loft; it's not far from the entrance hatch. I plan to leave everything labelled, with a diagram of the wiring I've done.

 

[EFLImpudence]

Oh, right. I didn't realise.

You can, indeed then, put the accessories near the fan.

 

[Grenage]

Tip top, thank you kindly.