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Topic Title: Fuse protection for extraction fans
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Created On: 11 January 2012 10:39 PM
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 11 January 2012 10:39 PM
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SKElectrical

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Iv been naughty as i haven't been fusing down to 3A when installing fans off a 6 / 10A mcb.
If you wire in 3 core and earth, (ie sw live & perm) how do you incorporate 3 amp fuse protection?
 11 January 2012 10:43 PM
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sparkingchip

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Get a different make of fan that does not state a 3 amp fuse is required in the instructions allowing the circuit protective device to be used.

Andy
 11 January 2012 10:48 PM
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OMS

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Originally posted by: SKElectrical

Iv been naughty as i haven't been fusing down to 3A when installing fans off a 6 / 10A mcb.

If you wire in 3 core and earth, (ie sw live & perm) how do you incorporate 3 amp fuse protection?


Well wire the line and neutral to the spur and then take your circuit from there - use a 3 pole isolator adjacent to the fan if you need local isolation - if not the the spur does the job anyway

Regards

OMS

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Failure is always an option
 11 January 2012 10:56 PM
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daveparry1

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Trouble is OMS if it's a timer fan that means wiring the bathroom light from the fcu too for the sw. live, better to just rely on the 6a mcb I think. I would only fuse down if feeding from a ring etc.

Dave.
 11 January 2012 11:04 PM
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sparkingchip

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I was serious about using a different make, why allow manufacturers to complicate things making installation take more time and materials?

Andy
 11 January 2012 11:07 PM
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SKElectrical

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Yeah i meant sw live, perm, neutral & cpc to be used with a timer fan.
Im thinking of 3A mcbs? Maybe 2 x in-line fuses for each (sw live & perm)?
 11 January 2012 11:10 PM
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OMS

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Originally posted by: daveparry1

Trouble is OMS if it's a timer fan that means wiring the bathroom light from the fcu too for the sw. live, better to just rely on the 6a mcb I think. I would only fuse down if feeding from a ring etc.

Dave.


Must be a hell of a bathroom if the light and fan exceed the capability of a 3A fuse

I don't disagree though - a 3A cartridge fuse offers bugger all protection to a fan anyway so straight off the 6A or 10A MCB is no "worse"

OMS

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 11 January 2012 11:10 PM
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SKElectrical

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posted by: sparkingchip
I was serious about using a different make, why allow manufacturers to complicate things making installation take more time and materials?


I know but electrifix do an inline fan 180 litres/hr for £60
 11 January 2012 11:17 PM
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sparkingchip

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That would be the Manrose at a guess.

Have a look at http://www.greenwood.co.uk/pro...ing.asp?product=AXS100
 12 January 2012 12:19 AM
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ebee

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Well the real world answer is

Most manufactures state a 3A fuse requried.

Most installers just rely on the 5/6/10A MBB/fuse for the cct anyway.

In practice not really a problem (but non compliant)

Will a 3A fuse offer better protection than a 5 or 6A MCB?
Not on your nelly

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 12 January 2012 12:30 AM
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SKElectrical

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Originally posted by: sparkingchip
Have a look at http://www.greenwood.co.uk/pro...ing.asp?product=AXS100


its ugly
 12 January 2012 06:40 AM
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jumpinjax

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There was a case in recent years where an electrician was taken to court by the insurance company because a house fire was caused by a jammed extract fan. He had not followed manufacturers instructions by fitting an inline 3 amp fuse therefore held liable even though as said in previous posts minimal overload protection would be provided.
 12 January 2012 07:54 AM
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anastasis

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Originally posted by: sparkingchip

That would be the Manrose at a guess.

Have a look at http://www.greenwood.co.uk/pro...ing.asp?product=AXS100


The instructions for that are a bit dated as they say "When supplied from a 5 amp lighting circuit no local fuse is required." You'd have to ask them if the same is true for a 6A circuit.

It also specifies a DP isolator, not a TP fan isolator which would make more sense.
 12 January 2012 08:38 AM
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davebp

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One option is that the fused connection unit is the isolator for both light and fan, but this means you can't turn off fan without losing the lights.

I think I'm sticking with FCU protecting permanant live only, then switched line into three pole isolator without output from FCU, then 3-core cable off to fan.

I can't see that the timer run-on input needs fusing at 3 amps, as this is surely just a switching signal to tell the fan to run, and not where the load is?

Dave.
 12 January 2012 09:17 AM
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AJJewsbury

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but this means you can't turn off fan without losing the lights.

Unless you have fan isolator too....

I think I'm sticking with FCU protecting permanant live only,

So pull the fuse and the fan it still live via the timer line? Doesn't sound ideal to me (and probably a breach of section 314).
- Andy.
 12 January 2012 09:39 AM
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spinlondon

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I think Dave is suggesting placing the fuse on the permanent live, before any switches.
 12 January 2012 09:41 AM
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daveparry1

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I still think no need for fcu if coming off a 6a breaker, i'd only use an fcu if feeding from a ring. (or somewhere else protected by a bigger breaker) The fan will usually be wired in 1.00mm or 1.5mm so the cable will be well protected and even if the motor is stalled for some reason I really can't see a motor of that small size generating enough heat to cause a problem. Not disputing the earlier post about an insurance claim but i'd think that was a cop-out by the insurance company, trying to wriggle out of a claim?

Dave.
 12 January 2012 10:04 AM
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anastasis

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Forget the insurance, it's a breach of BS7671 not to follow the manufacturer's instructions. You're misrepresenting yourself if you sign an EIC without listing it as a departure. And, of course, departures have to be of equivalent safety.

If they require the supply fusing, I'd suggest it has to apply to both the permanent and switched supplies. Likewise, isolation must isolate both of these (plus the neutral if specified).

You could have a fused (non-switched) spur supplying the light and the fan, and a three pole fan isolator for just the fan.

My own flat has no fuse and no isolator for the fan, and that's how it was done by the builders. And am I going to rip the bathroom apart to change that? You must be joking!
 12 January 2012 08:13 PM
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kaichung

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It's a bit like the immersion element scenario...
Some element manufacturers state a 13amp fuse is needed on a 3kW element, some only require a 20amp rewireable fuse. It all depends on the manufacturer's specification.
If I were you, for all new installs, I would put in the 3amp fused spur regardless of instructions, exactly as I would fit the 13amp fuse for the immersion elements.
 12 January 2012 08:37 PM
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sparkingchip

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I see anastasis read the Greenwood instructions in the link correctly where it states a 5 amp lighting circuit, however I fitted one today and have a hard copy of the printed instructions in front of me issue 6/ August 2010, which states "when supplied from a 6 amp lighting circuit no local fuse is required"also it does not mention a 3mm gap on switches either bringing up that old chestnut of "light switches and fan isolators don't have a 3mm gap".

Life does not have to be complicated, despite the efforts of some manufacturers with their installation instructions.

Andy
IET » Wiring and the regulations » Fuse protection for extraction fans

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