New bathroom fan. Isolator required?

[JohnW2]

It is (or a least it was) more common than being struck by lightning for a fan to grossly overheat and go on fire/smoke according to a couple of my fire brigade contacts - I mean actual fire/smoke type situations they have attended or investigated forensically, it does happen or it did happen ...

Fair enough. Even though they have been known to come up with some rather questionable ideas, you can but 'believe' what you have been told by fire brigade people.

My reference to lightning was, needless to say, rather tongue-in-cheek, to emphasise my point that it was (I presume) I very rare occurrence.

I do think it must be extremely rare. As I wrote, I undertook experiments (which I'm pretty sure I will have reported here) to se what happened when one of these fans got 'jammed' - with a view to determining whether a 3A fuse (as vey commonly 'required' by MIs) could/would achieve anything. What I found was that the current drawn in that situation never rose to anything remotely as high as 3A and also that, in most cases, a 'thermal cut-out' would operate before anything got serious hot, let alone 'burning'.

...... and they took the stance that a timed overrun fan needed an isolator close to the fan or say immediately outside the bathroom. Without timed overrun/humidistat etc it was not important because a flick of the lightswitch would suffice (although better for cleaning etc)

Did they also say that a 3A fuse was needed, I wonder?

Fan isolators (usually installed to facilitate maintenance) are commonly very high up on a wall (sometimes even on the ceiling). If I experienced this ('extremely rare') occurrence of smoke/flames coming out of a fan, I think I would be far more likely to head for the CU to isolate the circuit than to find a way to climb up and operator a 'high isolator' in a room which was 'on fire'.

Another thing I would say about the fire brigade's view (quite common is other contexts) is that they seem to have the idea that when an established fire has been initiated by an electrical fault, that the fire will 'go away' if the electricity supply is 'switched off' - and I don'gt think that is generally true.

One could, of course, always remain in the room throughout the 'timed over-run' period, in order to detect the first signs of smell/smoke (before there was significant 'actual fire') - but, of course, there would then be no point in having the 'timed over-run' in the first place

Kind Regards, John

 

[ebee]

LOL, |Pretty much as you say John,
I think the 3A fuse can be a bit of a "Red Haddock" in these situations, a 5A/6A OPD at origin would make me happy, I view the 3A fuse as a bit of a CYA exercise really.

Yes I did realise your lightning quote meant purely that it was quite a rare event but from what I`ve seen first hand plus what I`ve been told by Fire Prevention officers and Forensic Investigators then not as rare as we might think, whether that`s down to cheap imports or cheap components I can`t say but whilst not common it does not seem to be as uncommon as we might have thought. I think, at best, we might say that the Jury is still out on that one.
To get to my view I have tempered it with an inkling that some folks (experts) might sometimes have some tendency to put it down to electrics in some situations because of lack of evidence otherwise. I am sure that does happen on some occasions , hopefully rare but I would gauge it does a bit anyway. Nonetheless I have factored that in a little bit when forming my opinion, I have also factored in the mistaken beliefs/deliberate untruths of a fraction of folk who answered me when I asked "What happened here?".

A common example of the what happened here scenario is - "My lights have started acting strangely upon switching", they been OK for the last 5 years since I rewired the house but in the last few weeks strange switching effects have resulted. So as usually I ask if any work has been done anywhere in the house.
Sometimes if I ask about decorating I get a yes "But nobody has touched any of the switches", I take that answer with a pinch of salt.
I reckon that sometimes that are deliberately using untruths because they don`t like to admit they`ve beggared up the connections but sometimes they are actually unaware that a relative has actually beggared it up because they asked that relative and that relative told them "But nobody has touched any of the switches", and they believed it, still an untruth but not a lie in my opinion.
Sometimes you get to know the extent of the decorating or can see it and realise it looks different to last time I saw this X years ago and it narrows it down to the switch(es) that have been disturbed (removed and refit) so you know where to look but you gotta be careful so as not to let the customer know that you are disregarding their "Not touched owt!" statement. I sometimes aids fault finding if you actually know what has been touched and where the mistake might have originated.

Anyway the point is that there might sometimes be wrong info/conclusions so we need to factor that in too.

Yes fan isolators I tend to put higher up on the wall , certainly out of very easy reach because in normal circumstances they are not to be used but for maintenance or urgencies they can be used maybe by hand or maybe using a short stick. I have seen such isolators at common use mounting heights but I think that defeats the object of allowing the fan to overrun because it becomes a normal on/off switch in usage. The other extreme is where someone has put it only reachable by getting up step ladders, removing a loft hatch and feeling around for it - almost completely hidden! Why on Earth do that? unless there is an extreme need to do so.

No the fire will not necessarily go away when electric is disconnected but the source might sometimes do so, worth a try, so a quick easy fix might help the situation and might mean you can still keep the light on to watch what is happening . Lots of normal people do not have torches handy or emergency lighting dotted throughout their house.

 

[mcprinter]

OP here.
I am going to fit an isolator switch. Makes sense if the fan needs replacing or cleaning.

Fused or non-fused?
Circuit is on a 16A MCB

 

[Murdochcat]

OP here.
I am going to fit an isolator switch. Makes sense if the fan needs replacing or cleaning.

Fused or non-fused?
Circuit is on a 16A MCB

Are you sure about the 16A MCB if the power is coming off the lighting circuit?

If its a 6A MCB the likely hood is that the MCB would trip before a 3A cartridge fuse blows.

 

[johnny2007]

when I rewired the house last year, the electrician insisted on a fan isolator.
Not a problem at the time as I had all ceilings exposed and no plaster.
I find it convenient to turn off at night so I don't get woken if someone uses the bathroom.

 

[ebee]

when I rewired the house last year, the electrician insisted on a fan isolator.
Not a problem at the time as I had all ceilings exposed and no plaster.
I find it convenient to turn off at night so I don't get woken if someone uses the bathroom.

That, in my opinion, is abuse of a fan isolator, using it as an operational switch is not why it is there.
Cleaning, replacing etc should be it`s intention, not operating it, that is the job of a functional switch or sensor.

 

[mcprinter]

Are you sure about the 16A MCB if the power is coming off the lighting circuit?

If its a 6A MCB the likely hood is that the MCB would trip before a 3A cartridge fuse blows.

Yes.
House is extended sideways. The 16A is the old part of the house and outside lights.
Newer 'wing' is on a 6A.

 

[JohnD]

I find it convenient to turn off at night so I don't get woken if someone uses the bathroom.

Good modern fans with ball-bearing motors are extremely quiet and will not be heard if you shut the door.

 

[Murdochcat]

Yes.
House is extended sideways. The 16A is the old part of the house and outside lights.
Newer 'wing' is on a 6A.

So you are 100% sure the lighting is protected by a 16A fuse or MCB

That isn’t great and needs addressing as most lighting circuit accessories are 10A max

Does the circuit have RCD protection?

 

[JohnD]

A 16A circuit was usually intended for an immersion heater.

 

[mcprinter]

So you are 100% sure the lighting is protected by a 16A fuse or MCB

That isn’t great and needs addressing as most lighting circuit accessories are 10A max

Does the circuit have RCD protection?

Don't think it is RCD protected?

 

[JohnD]

There's a severe shortage of circuit-identifying labels.

 

[mcprinter]

There's a severe shortage of circuit-identifying labels.

Piece of paper out of shot with circuit functions.

 

[Murdochcat]

Piece of paper out of shot with circuit functions.

Have you checked them?

Definitely no RCD within those photos

 

[JohnW2]

OP here. I am going to fit an isolator switch. Makes sense if the fan needs replacing or cleaning.

Fair enough. As has been said, it's entirely your decision, given that there is no regulatory requirement.

Do I take it that the room has no window (i.e. 'natural light', during the hours of daylight)?

Kind Regards, John