Extractor fan - Do I have to fit a fuse?

[tom.harrigan]

I'm sorely tempted not to bother fitting a 3A fuse to my bathroom extractor fan. I don't see the point!

T

[ARWadsworth]

Who says you need to?

Adam

[tom.harrigan]

I sense a leading question - the manufacturer.

T

[ARWadsworth]

I have seen some manufaturers that say that.

Which one is it this time?

Adam

[tom.harrigan]

Actually it's all of the ones I've looked at - though Xpelair do specify a 5A fuse. Which manufacturers don't specify a fuse, as I'll get one of those...

T

[John]

I would want to if it was fed from the ring main.

If fed from the lighting circuit then I would be reluctant.

[tom.harrigan]

My bathrooms have their own circuits - from 6A RCBOs.

T

[Man at B&Q]

SO if something goes wrong with it, it takes out all the light as well. That's useful.

[Fredxx]

Hmm - if there was a fault, it would probably take both out. So I would advocate the one 6amp breaker, or a much lower ampage fuse. Even then a standard cartridge fuse would blow and a fast MCB would also go at the same time!

[Man at B&Q]

messagenews: [e-mail]...

Maybe not if it was individually fused.

[tom.harrigan]

[e-mail]...

Well yes, if "something" goes wrong with the fan then it could trip all the bathroom lights and vice versa. However, some manufacturers recommend the fuse be placed upstream of any connection to a light (so that both switched and permanent live are fused), which has a similar effect.

I would prefer to isolate the fan and switch the RCBO back on, than hunt around for a spare 3A fuse!

T

[ARWadsworth]

Not a problem. Turn off the fan isolator and reset the RCBO.

Not a big deal.

Adam

[ARWadsworth]

Then just fit a fan isolator as required by the rules. No need for a seperate fuse.

Adam

[John]

A bulb blowing is more likely to trip the mains than a fan fault IMHO

[Dave Osborne]

Well you *absolutely* should fit a fuse.

A number of house fires have attributed to extractor fans catching fire. The manufacturer does not want to tell you this, so they conveniently forget to mention *why* they recommend a 3A fused spur.

Google "extractor fan causes fire"

e.g.

Smoke without fire?: The London Fire Brigade is citing extractor fans as a cause of fires in the home

Article Abstract:

Extractor fans can be the cause of fires in the home and the London Fire Brigade's Investigation Unit has attended 97 fires involving extractor fans over the past three years. The design and the manufacture of the fans is an issue and fans that are not produced to appropriate British Standards or the equivalent can be legally sold. Fans should be installed in accordance with manufacturers' instructions and they should be properly maintained and kept free from dust, fluff and grease.

[ARWadsworth]

A 6A B type RCBO will probably trip before a 3A BS1362 fuse.

Adam

[js.b1]

Indeed, generally 5*In for Type B and 7-10*In for BS1362.

I'm always wary of cited fire statistics, too much grouping occurs along with an underlying "default cause". Those fire stats are perhaps masking what *kind* of extractor re risks.

I suspect many are in fact cooker hood extractor fires caused by clogged or missing grease filters, flexi-pvc, clogged outlet flyscreen, jammed backdraught shutter or jammed/interlocked louvre shutter. There is less probability of a conventional bathroom/kitchen window/wall extractor causing a fire - but certainly not zero probability.

The problem common to most is the use of AC fans where AC motors firstly require quite significant cooling (or overheating results) and secondly current draw peaks at fully stalled condition (causing thermal runaway). To prevent overheating the normal cutout is a bimetallic strip, however this can fail, be omitted or simply inadequately tailored to the fan assembly. The fan assembly needs to be designed so as not to catch fire or melt in such a situation, historically AC fans used to use metal rotors, metal struts & metal housings to dissipate the thermal energy of a stalled fan (as well as bimetallic thermal cutout).

DC fans should have replaced AC long ago in many domestic applications, what is outrageous is the prices charged because for the most part the fan is cheaper and lasts longer due to lower thermal loading - the cost is a simply PSU. No doubt DC extractors will then suffer power supply fires or exploding capacitors or such like.

Cooker hoods are indeed quite notorious for fires where neglected, I'm not sure they incorporate glass-bulb thermal fuses as a backup cutout.

[Dave Osborne]

Maybe on a short circuit or an earth fault. A 3A fuse is going to blow before a 6A breaker on a long-term moderate over-current - which clearly is the likely fire-causing scenario in this case.

[Pete Verdon]

A work colleague of mine suffered exactly this.

Pete

[tom.harrigan]

If they need a fuse, why don't they come with one?

T