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Topic Title: 3amp fuse on fans again.
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Created On: 25 April 2012 03:02 PM
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 25 April 2012 03:02 PM
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aligarjon

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just reading another post on extractors and i didn't want to hijack it but it jogged my memory to a fan i fitted a few weeks ago. The instructions did say i must use a 3amp fuse, then in brackets it said (uk only). whats that all about, its either a safety issue or its not.

Gary

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 25 April 2012 03:17 PM
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Legh

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Firstly, would a 3A BS1362 offer discrimination against a 6A BS EN 60898 in the case of a fault?
I had a problem with two underfloor heating elements protected by a 13A fuse. When the smaller one of the two failed, it took out a 50A breaker as well.
Localized fusing appears to be a waste of time and is probably a through back to when final circuits were protected by fuses and not breakers.

Legh

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 25 April 2012 03:33 PM
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AJJewsbury

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Firstly, would a 3A BS1362 offer discrimination against a 6A BS EN 60898 in the case of a fault?

Depends on on the fault - those inside an appliance aren't necessarily of negligible impedance between L and N or PE. Shorted turns on the motor winding, partly fried electronics, or even an impeller clogged up with dust, probably looks more like a moderate overload to the fixed wiring.
- Andy.
 25 April 2012 03:46 PM
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Legh

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Fair enough, but these methods of protection are built into the appliance and as you say are not negligible as might a separate fuse link would be.

Legh

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 25 April 2012 06:36 PM
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weirdbeard

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Originally posted by: aligarjon

just reading another post on extractors and i didn't want to hijack it but it jogged my memory to a fan i fitted a few weeks ago. The instructions did say i must use a 3amp fuse, then in brackets it said (uk only). whats that all about, its either a safety issue or its not.



Gary


Hi gary, having looked into it a bit, it seems some fans are built on the cheap and don't incorporate their own thermal overload protection, so for the sake of a few pennys, (or yennies, whatever they call them), the onus is then placed on the installer by way of the instructions to provide an external fuse to provide protection against fire by overload - though I'm not convinced that with a 1 A fuse if even only a sustained 230W, let alone 690W for a 3A is being dissapated into a small plastic enclosure rated at 10-15W will be much help in an overload protection sense- with that kind of heat being generated within the fan would just melt!
 26 April 2012 08:19 AM
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MrP

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IMHO
Pointless fitting a 3amp local fuse if the circuit protection afforded complies with current carrying cap of the cable
If you did fit a local BS1361 fuse how could you guarantee that the smaller 3A local fuse would operate first if the circuit protection feeding it was of another BS standard you couldn't therefore pointless
MrP
 26 April 2012 09:05 AM
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broadgage

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Seems a rather pointless instruction, especialy as the 3 amp fuse is not required in other countries.
Is is really safe in Germany, but dangerous in the UK without the fuse ?

However to ensure compliance with the regs, manufacturrers instructions should be followed, even if pointless.
Fused connection units are cheap.
 26 April 2012 09:22 AM
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gkenyon

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Maybe the answer is that the LX circuit in the UK may well NOT be protected by a B6, but by a 5 A rewireable?

Why don't you formally ask the manufacturer the question. It does seem a little silly that in other EU countries, a B6 is OK, but in the UK, where prospective fault currents may well be higher (i.e. B6 more likely to operate from the magnetic trip before a 3 A BS1362 even thinks about getting warm), you apparently need B6 + 3 A spur/FCU: is this overkill?

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 26 April 2012 10:27 AM
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rogerbryant

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In the mainland EU it is likely that the bathroom extractor will be protected by a 10 or 16A OPD.

Is it possible that this additional 3A fuse requirement for the UK is protecting agains the possibility the the fan is connected to a RFC with a 30 or 32A OPD?

Best regards

Roger
 26 April 2012 11:34 AM
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GB

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Whether the additional protection is required (1A 2A or 3A dependent on manufacturer) would depend on the type of fault but probably just another way for the manufacturers to make things "cheaper" and adding to there t&c of installation so as they are very unlikely to be found liable for any damage caused by a fault at the fan, they also include things like regular cleaning and maintenance.
In summary probably just an a*s* covering operation, I dont see why they cant install inline fuses and thermal cut out to the fans??
I once witnessed a fire test on a fan (Vent Axia fully compliant with standards) and the fan housing just burned and dripped away merrily, the standards must be "strange" to say the least!!

 27 April 2012 09:59 PM
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antric2

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Evening all,
Manufacturers instructions should be followed but where fans are concearned,the manufacturers seem to be misinformed about fusing.
Fuses are used to protect the cable supplying the appliance and not the appliance,in this case the fan.
If a fan melts then eventually the fuse will go with a bang but it will get well on its way before taking fuse or breaker out.

3A FCU is only pennies but it means mauling about breaking into the light circuit so can be a bit of nuisence sometimes as a 3 pole isolator also has to be fitted .

This is a judgement call by the installer me thinks!
Regards
Antric
 02 May 2013 08:09 PM
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weirdbeard

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Originally posted by: AJJewsbury

or even an impeller clogged up with dust, probably looks more like a moderate overload to the fixed wiring.



Hi All, sorry to drag up this old subject again but I just happened to remove an older wickes 4inch fan, so I checked it out - (only a short term test at the moment! ) There is no internal thermal cutout device.

Running normally measured watts= 21
Stalled watts = 29

Summary so far:

3A fuse - pointless!
 02 May 2013 10:05 PM
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AJJewsbury

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What about: "Shorted turns on the motor winding" or "partly fried electronics"? (er, perhaps I should say "don't try that at home"!)
- Andy.
 03 May 2013 12:41 AM
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kengreen

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I'm out of my territory here but intrigued.

So far the talk has been all about current ratings without even a mention of the other parameters that affect fusing. For example fuses also have a voltage rating which indicates their ability to melt and clear a fault instead of replacing the fuse-wire with an arc.

They also have a time-delay function which determines whether they blow at once or wait and see.

A last problem is that a fuse is the least reliable form of defence not helped at all by the necessity to batch test.

Ken Green

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 03 May 2013 05:38 AM
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Jaymack

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I've attended a fault where the houseowner has said "BTW, can you also have a look at the bathroom fan, it's not working"

In this case, it was simply the fact that the impellor was clogged with airborne particles of cotton etc.. These are synchronous motors, and can tolerate a stalled condition for a long period of time, without undue effects; how long is dependent on the heat input versus the heat dissipation to the surroundings, but there is a possibility of fire, caused by fan over temperature.

I've seen a fatal fire in a residential caravan in South Africa, caused by a window extract fan installed over a kitchen hob. From the evidence, the impellor was found to have been clogged with cooking fat. These extract fans are also driven by synchronous motors. Did the user read the instructions on routine cleaning and comply?, probably not, giving credence to the "fit and forget" mentality. Would you as a landlord, now specifically give instructions on cleaning fans, as a condition of the lease? You decide.

Whether a 3 Amp fuse would eventually operate in the event of a stalled condition, is not known to me; but if the manufacturer seems to think that it would, presumably from type test results; then it would be foolish to ignore the requirement. No, I didn't check for a fuse in the above bathroom fan incident.

Regards

Edited: 03 May 2013 at 05:45 AM by Jaymack
 03 May 2013 09:03 AM
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SKElectrical

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if it's a real pain to install a 3A fuse near the bathroom just install it next to the C/U.
I fess I won't be bothering.
I do worry a little because I install the inline ceiling fans mounted directly to the roof rafters.
 03 May 2013 03:20 PM
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daveparry1

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So that means all the lights on that circuit will be on the 3 amp fuse then SK ?

Dave.
 03 May 2013 07:46 PM
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SKElectrical

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3A is plenty these days for upstairs lighting. In fact come to think of it, its cheaper to put in a 3A mcb £2.80 !! haha I might even start doing that.

http://www.tlc-direct.co.uk/Pr...l?source=shopping.com

Could even swap a few lamps to LED it's that cheap.
 05 May 2013 09:24 PM
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Zoro

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Some manufacturers did not require a 3A BS1362 to cover permanent feed and switched feeds, but most do now.

I have spoken to a MD of british manufacturer, who agreed that a 3A fuse is not going to protect a 15W motor but they require a 3A fuse to cover themselves when one goes bonfire. The courts are happy with an attempt at protecting themselves, so all the manufacturers require a 3A fuse.

I have spoken to Airflow Technical, they were totally disinterested, we say fit a 3A fuse, that is the end of it. Even when I suggested that if they fitted a device on the board, that would blow and scrap the fan for commercial reasons, not interested.

Just like Manrose who had a hole in their in line extractors where the water would fill the PCB and connectors with water/condesation. This is fixed in the late 2012 models, but making a 3A fuse a manufacturers requirement is cheaper, than designing it correctley in the first place.

Once you are in a position to write your own regulation, why should you bother, a bit like the Schemes really.
 05 May 2013 10:08 PM
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leckie

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It's easy folks, buy greenwood airvac or vortice. Rock solid reliable and the 3a fuse can be omitted if protected by a 6a mcb.
IET » Wiring and the regulations » 3amp fuse on fans again.

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