Extractor fan - is a 3amp FCU really necessary?

[Jim Ingram]

Hi,

Just purchase a (humidity controlled) fan to fit in the bathroom (probably in Zone3/outside zones depending on height).

Requires the usual perm.live, sw live and Neutral. I was initially going to take the L,N and SW L from the bathroom light fitting via a 3 pole sw fitted near the bathrom ceiling(outside zones, I know ideally it would be outside the bathroom but I don't envisage anyone touching it under normal circumstances).

The installation instructions, however seem to suggest (but not insist) that the fan is powered by a 3amp FCU.

I could do this (I'm not sure is a 3amp fuse would necessarily descriminate between a 6 amp MCB anyway? I guess it might) but it complicates matters as, even if fiited a 3A fused FCU between light fitting and fan I'd need to run a new sw live (fused at 3A presumably). I guess I could swap the existing light sw for a double pole switch and use that to provide a second sw live (from the 3A FCU) but I don't want to unless its actually neccessary.

Many Thanks

Jim

[Owain]

Fairy nuff.

Provided your lighting circuit is on a 6A MCB that should provide adequate protection, if the destructions do not insist on 3A.

The eleganter way of doing it would be to pull the bathroom light cables back into a junction box in the loft space, run a L&N to a 3A FCU and thence onto the ceiling rose from which you can obtain L and SwL for the fan as normal i.e. fuse both the light and fan.

Owain

[Rumble]

Jim Ingram said the following on 04/02/2006 19:57:

I can't cite a reference (I think it was one of the Electrical Contracting magazines), but it came to light a few years ago that a significant number of house fires were attributed to extractor fans failing (stalling) and then catching fire. Since then it has been best practice to wire extract fans by a fused spur and fuse down to 1 or 2Amp to provide additional protection.

If you google for "extractor fan fused spur" you will note that pretty much every manufacturer, supplier and local authority makes the use of a fused spur for an extractor fan a requirement (or at least an expectation).

[Jim Ingram]

expectation).

Thanks. Not sure I've ever seen 1 amp plug fuses. Another option that occurred to me was to get a couple of fuse holders from RS or maplins. I could then mount these on a blank cover fitted to a dual pattress/back box next to the isolator switch. I'd guess wiring the fuses between 3p isolator and fan would be best. This would amount to a fused spur and have the advantage of being able to fit a sensible fuse for the rating of the fan. I assume from what you said above these fans don't normally have an integral fuse. Would what I'm suggesting be acceptable? I guess there might be a conflict with the regs in having two independently fused lives feeding one appliance (but in practice shouldnt be an issue provide I use a 3 pole isolator).

If this isn't OK I think I'm go with Owains suggestion

Cheers

Jim

[David Hansen]

On Sat, 4 Feb 2006 19:57:35 -0000 someone who may be "Jim Ingram" wrote this:-

There never has been a prohibition on switches in rooms containing a bath or shower. If there was then they would need to extend it to all other basins.

What there is (and was under previous regulations) is a prohibition on switches being within reach of people who are in the bath or shower [1]. One of the reasons for this is that the feet and hands normally provide a fair degree of insulation, but this is not the case if one is in a bath or shower. Switches out of reach of someone using the bath or shower are fine. For things like fans switches beside the fan also have the advantage that someone else can't turn them on while someone is working on the fan.

[1] I am aware of the exceptions.

[Andrew Gabriel]

BS1362 1A fuses do exist, although they shouldn't be used in plugs as they are not ATSA-approved (which would be a PAT test failure).

[Rumble]

Jim Ingram said the following on 05/02/2006 10:01:

I would go with Owain's suggestion TBH. There's no good reason not to implement a standard solution.

HTH.

[Dave Stanton]

Brilliant, you repost all the previous post just for a one line answer.

Dave

[Jim Ingram]

Except that even a 1 amp fuse is still in excess of whats required for a

30W fan. If prevention of fires is the driver for putting in a FCU then it's probably a poor half measure. I'm still not convinced a 3amp FCU vs a 6amp MCB would offer that much additional protection at all. I could well be wrong but without studying the failures of such fans and stalling currents in detail it's impossible to be certain.

Actually I think the best solution would be for fan manufacturers to incorporate a thermal fuse on or near the fan motor (eg. rs 204-7382). I'm tempted to fit one myself anyway (in addition to the specified FCU).

Cheers

Jim

[<me9]

I don't think I've seen a recent small fan/motor that doesn't incorporate such a fuse.