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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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 12 January 2012 08:43 PM
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perspicacious

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Where there is more than one fan in a house, I've seen contractors use a 3 A circuit-breaker in the CU and wire those rooms off it.

Regards

BOD
 12 January 2012 08:49 PM
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sparkingchip

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I wired the central heating in a house to it's own B3 MCB in the Consumer Unit with a double isolator by the boiler, the British gas service engineer did not like it as they are told to take the fuse out of the SFCU put it in their pocket then attach a warning sign with a cable tie through the fuse holder.

Andy
 12 January 2012 10:27 PM
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Grandfortune

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cant find the article now, but a few years ago a Hotel burn down(partly) due to a fan stuck on, Insurance company asking questions to Vent Axia, Vent Axia stating that fan were not on a 3 amp fuse, Sparky was liable.
 13 January 2012 06:18 AM
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ebee

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Originally posted by: sparkingchip

I wired the central heating in a house to it's own B3 MCB in the Consumer Unit with a double isolator by the boiler, the British gas service engineer did not like it as they are told to take the fuse out of the SFCU put it in their pocket then attach a warning sign with a cable tie through the fuse holder.



Andy


I`m lost on this one. What difference would it make to the gas engineer what size the breaker was 3/6/10/16/20/32 etc if the 3A or 5A SFCU fuse was in his pocket?

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 13 January 2012 09:04 AM
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AJJewsbury

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I`m lost on this one. What difference would it make to the gas engineer what size the breaker was 3/6/10/16/20/32 etc if the 3A or 5A SFCU fuse was in his pocket?

'cos there wasn't an SFCU and hence no fuse - just a 3A MCB and a DP switch/isolator.
- Andy.
 13 January 2012 08:11 PM
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breaker

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I use Click Mini Grid 3 pole fan isolator in conjunction with an inline fuse holder, sits in a 2 module yoke plate and costs about the same as a standard 3 pole fan isolator. If you are switching the fan on with the lighting you need to feed the lights through the fuse to ensure the permanent live and switched live to the fan are protected by the 3A 1362 fuse.
 14 January 2012 05:27 PM
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dp11

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I'm not Part P. House is to 16th so lighting circuit is not RCDed just a 6A MCB.

I want to replace the current extractor fan with with a new one in my bathroom ( Zone 2). The current wiring has the main light on the lighting ring with the as you would normally find. From the ceiling rose a 3core cable with L/N/E and switch L goes off to the isolator and then the fan. The shaver socket is also on the lighting ring.

The new fan has a requirement for a 1A fuse. The wiring method as in the instructions for the new fan is to fuse before the ceiling rose ( so as to fuse both live and switched live). This would require move the ring to a FCU in the loft and making the ceiling rose a spur. This would be the neatest solution. I have the test kit to check my work.

So the question is this "Notifiable Work" ? The Fan could be considered and like for like, the FCU on the lighting ring would be in the loft so not in Bathroom, but their would be minor modification to the wiring in the ceiling rose to remove the ring and feed it from the FCU

I'm thinking that the work isn't notifiable but would just like to check.
 14 January 2012 06:24 PM
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perspicacious

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"The current wiring has the main light on the lighting ring with the as you would normally find."

I have only ever seen lighting on a radial circuit edit to add, never on a rfc.

Regards

BOD
 14 January 2012 06:51 PM
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ebee

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you never been to our neck of the woods BOD.
One contractor for many years used to wire domestic lighting as a 1.0 T & E ring feeding pendants on loop in method.

Don't ask why

-------------------------
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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 14 January 2012 06:53 PM
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ebee

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Originally posted by: AJJewsbury

I`m lost on this one. What difference would it make to the gas engineer what size the breaker was 3/6/10/16/20/32 etc if the 3A or 5A SFCU fuse was in his pocket?


'cos there wasn't an SFCU and hence no fuse - just a 3A MCB and a DP switch/isolator.

- Andy.


Thanks for clarifying AJJ, I hadn`t realised no SFCU therefore no fuse present

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 15 January 2012 12:05 AM
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kirchoffs

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About 2-3 years ago i remember seeing a fused triple pole fan isolator, standard 1-gang size. It was in one of the Qvs,Electricians mate,TLC type of catalogue ,i cannot remember the make and have never seen or heard of one since.

I,ve searched the internet several times with no luck, i remember vaguely it was one of the cheap brands like Vimark,pms etc.

Can anyone else remember seeing it ?,

Regards Dominic
 15 January 2012 12:22 AM
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sparkingchip

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How to wire a bathroom extractor fan with a switched live from the lighting has been a issue for around thirty years, it is good to see the old issues never get resolved, but just keep trailing on and on and on and on and on and on and one etc. etc. etc.

Andy
 15 January 2012 11:36 AM
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unshockable

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I have done this sometimes; the trick is to replace the light switch with an 2 pole isolator.

From one side of the isolator, switch the light as normal.

From the other side of the isolator, switch the output of a SFU fed from the light. No need for a fan isolator as the SFU does that job and is lockable as stated. Don't forget to label "3A only".

Jobs a good un.

Simon
 15 January 2012 12:57 PM
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weirdbeard

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 15 January 2012 02:13 PM
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unshockable

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All those cuttings certainly make you think. What code would this be with a periodic? I remember this not been coded and the subsequent fire being blamed on the inspector.

Would a 3A fuse have stopped it? Would a blown 3A not be replaced with a 13A? If so important why don't the manufacturers fuse internally? Can these fans really be "fit for purpose" under the Sale of goods act?

Simon
 15 January 2012 04:15 PM
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sparkingchip

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Internal thermal fuse required?

Cutty Sark?

Edited: 15 January 2012 at 04:59 PM by sparkingchip
 15 January 2012 05:05 PM
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weirdbeard

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Originally posted by: sparkingchip

Internal thermal fuse required?


With out any evidence to back this up my suspicion is that ignition of lint build up is a more likely cause of the fires than the lack of a 3 amp fuse on a circuit with a 6A mcb which is the norm in a vast amount of bathroom installations - I would have thought that in the event of a fault within a fan housing sufficient to pop a 3A or even a 1A fuse there could be a spark of sufficient energy to ignite a build up of general fluff, hairspray laquer etc in the fan itself and any associated ducting.

Another thought I've just had is theres also the possibility that some fires could be non electrically related (but blamed as thus), caused by a more old fashioned method where simple friction caused by moving parts clogged by lint build up could rub together eventually producing enough heat to cause an ignition.

If I am anywhere near the mark with this lint theory it suggests to me that the electrical supply is unlikely to prevent a fire started by a fan occuring whether it is protected by a 6A mcb, 3A fuse, or thermal cutout, or all three, as once a fire has started no electrical protective device will put the fire out, but regular cleaning of fans and ducting would be a good way of reducing the risk.

edit to add:

Also, aren't fans themselves likely to be constructed of non-flame propagating plastic, ie, once the source of ignition is removed the materials are self extinguishing, which suggests where a fan is said to catch fire it is more likely that there is a secondary substance which could result in ongoing flame propagation?

Edited: 15 January 2012 at 05:19 PM by weirdbeard
 15 January 2012 05:32 PM
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sparkingchip

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Agreed.
 15 January 2012 05:42 PM
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daveparry1

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I agree too, I also think that when they can't really identify what actually caused a fire it is usually blamed on "electrical"!

Dave.
 14 November 2012 02:43 PM
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pmhetherington

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Hi folks,

I'm reviving an old thread as this seems to be the most appropriate place for this question.

I have a bathroom fan, a 3 pole fan isolator, and a circuit switched through the light switch giving live, switched live and neutral. The lighting circuit is on a 5A fuse (yes, a new consumer unit would be a good idea - not yet) and for reasons of convenience/access I don't want to fuse the bathroom lights at 3A, but the fan instructions do state that a 3A fuse is required. The supplied circuit shows this going before the switch (so it fuses live and switched live) but in my case it will have to go afterwards, which presumably means I need two 3A fuses (although arguably the switched live is a bit irrelevant and I could just fuse the live?).

In short, same old problem.

I am intending to fit (effectively) an in-line fuse (or fuses) adjacent to the fan isolator; the problem I have here is lack of space, so I am wondering if anyone knows of a fuse holder which fits in one of those architrave light switch boxes, or some equivalent which needs to be smaller than a standard 1-gang socket box. (Up to about 2/3 of the size will fit). A quick online search has thrown up a couple of possibilities with soldered terminals, which is not what I want at all.

I should mention that the fan isolator is in a surface mounted box and something which looks similar (but smaller) would be ideal, though not essential.

Thanks,
Phil
IET » Wiring and the regulations » Fuse protection for extraction fans

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