Adding an extractor fan off of a 6A lighting circuit.
Installation instructions specify a local isolator (as I would anyway) so 3 pole isolator will be used.
Switching L SL and N however should I have an FCU upstream of the live?
It would be 6A fused as specified which seems pointless the RCBO will trip before the fuse.
Also if you fuse the live feed the Switched live to the fan is still connected even with the fuse pulled.
I think the 3 pole isolator achieves all I need to re regs and the whole circuit is protected by a 6A RCBO.
 
Normally I would agree, however there is a case (somewhere on this forum) where same thinking was used and the person did not fuse the fan to 3a as per Manufacturers instructions and a fire resulted. Of course the contractor suffered disastrous reverses as a result! And today in fact like you I am going to do exactly the same as you with a bit of an Ohh-err moment thinking about that. Will follow manufacturers instructions or "give consideration" to. But how do you imagine a two pole fuse works? And if one goes on PL and not on SL what then...
 
I agree with V on that one - search through the related and one post contained the function of having a fuse within the three pole isolator. Covers you then in both instances. I thought I'd saved it to screenshot but I've got a lot of screenshots and not enough time.
 
For the case you've given, I generally add a SFCU with a 3A fuse and run the whole bathroom lighting off it to save the complexity of worrying about fusing the PL and SL separately, and provide a 3 pole isolator regardless of what the instructions may say.

Whilst some fans don't require the 3A fuse down, I think it's better to be safe than sorry especially as you never know who may come along after you and just replace the fan.
 
The fuse element in the combined unit is internal separate so the fuse still only covers L or SL not both.
Having read the instructions with Fan no fuse is mentiined only a dual pole isolator. And that should be a 3 pole for my unit.
I like the idea of fusing the whole bathroom circuit but then don't we fall foul of the reg for diversity of circuits?
Fan shorts and the lights go off...
I know the SL is only a trigger feed and not a load so my money is on FCU on tge L.
 
There was recently another thread on this and RB did a diagram to show how the single fuse in the TP can protect both lines.
I go with SparkyChick though, install unswitched FCU with 3A fuse to protect both the light and the fan and fit a TP isolator just for the fan.
Division of circuits is irrelevant.
 
The "fusing the live and the switched live" concern never causes me any problem because I never have a extractor fan triggered by the light,I always use a switched fused spur for isolation and fusing combined,along with the fans own means for triggering(pull cord or remote switch) it satisfies all any fan requires

My opinion has always been that triggering the fan using the light is p poor design
The lighting requirement and the ventilation requirement in all Bathrooms are sometimes two very separate functions
 
I like the idea of fusing the whole bathroom circuit but then don't we fall foul of the reg for diversity of circuits?
Your lights are on the common lighting circuit in any case!

IF you decide to have an FCU, IMO this needs to be in the line feed BEFORE the bathroom light, that way you fuse both the permanent live as well as the switched live.

However, the whole thing is nuts. Lets assume there is a 6A MCB protecting the whole lighting circuit., Now you introduce a BS1361 3A fuse just for the fan and light. HAve a look at the discrimination graphs and tell me which device trips first in the event of
1. Overload (unlikely)
2. High current short circuit.

Boo Murdock got there first…
 
Well of course the MCB would (or RCBO in this case)
So what's the point? Aren't we adding more elements into the equation?
 
Here's the post from @Richard Burns for reference.

http://www.electriciansforums.co.uk/threads/extractor-fans-in-bathroom.108900/#post-1171394

It's a neat solution, but probably requires more changes depending on the existing installation.

In terms of leaving the SL unprotected, I thought long and hard about that and whilst I think the biggest risk of fire is from the motor stalling or winding failure and the associated heat, if there is a timer/pir/humidistat involved there is a control circuit and we have no way of predicting the failure modes this may present. It's entirely conceivable that a component could fail and result in a SL/N short, so I've tended to go belt and braces.

To address your point @Des 56 . I generally concur, but the customer wants what the customer wants and sometimes no amount of 'have you thought about doing it this way' brings them to your way of thinking... have yet to try physical 'persuasion' with a heavy object, maybe one day ;)

@Pat H, @Taylortwocities... yes, we are adding stuff and no it's probably not strictly required in terms of circuit protection, but reg. 134.1.1 includes this "The installation of electrical equipment shall take account of manufacturers' instructions". If it's required by the instructions, it must be there.
 
I should have added to that, anything else is personal preference. I prefer belt and braces so I generally fuse down for the fan/bathroom lights, depending on the fan control mechanism and if it has a trigger input, I would add a 3p isolator regardless of whether the manufacturers require it or not because IIRC it's stipulated elsewhere in the regs.
 
Your lights are on the common lighting circuit in any case!

IF you decide to have an FCU, IMO this needs to be in the line feed BEFORE the bathroom light, that way you fuse both the permanent live as well as the switched live.

However, the whole thing is nuts. Lets assume there is a 6A MCB protecting the whole lighting circuit., Now you introduce a BS1361 3A fuse just for the fan and light. HAve a look at the discrimination graphs and tell me which device trips first in the event of
1. Overload (unlikely)
2. High current short circuit.

Boo Murdock got there first…
That'll be a BS1362 fuse:p
 
i'm with des. i'm not a fan of triggering the fan with the light ( pun intended, so there ). separate switch for fan every time. in our gaff, it's a 4 way grid outside shower room... shower room lights, fan, foyer light, soffit lights (PIR override).
 
The fan is a humidistat fan and very quiet. So no real issue with it coming on with the light.
An outside switch isn't always the most convenient if you discover a need for sudden ventilation...
 
[QUOTE="Taylortwocities, post: 1247782, member: 11045]
Lets assume there is a 6A MCB protecting the whole lighting circuit., Now you introduce a BS1361 3A fuse just for the fan and light. HAve a look at the discrimination graphs and tell me which device trips first in the event of
1. Overload (unlikely)
2. High current short circuit.
…[/QUOTE]

Hi - so I did that, and what I found was for a mythical 8A current (1), the 6A mcb will never trip, but the 3A fuse melts somewhere between 0.3s and say a couple of minutes. High current faults are cleared by both (2), and at 30A it's possible the mcb will be quicker, as you say :)

Being of unsound mind, a while back I did try to create a fault with a timer fan to give this awkward small overload current, but I failed and ate chocolate instead.
 
Hi - so I did that, and what I found was for a mythical 8A current (1), the 6A mcb will never trip, but the 3A fuse melts somewhere between 0.3s and say a couple of minutes. High current faults are cleared by both (2), and at 30A it's possible the mcb will be quicker, as you say :)

I'm glad you've posted that because I did exactly the same and drew exactly the same conclusions, but didn't want to overstep the mark as a relative newbie :)
 
The fan is a humidistat fan and very quiet. So no real issue with it coming on with the light.
An outside switch isn't always the most convenient if you discover a need for sudden ventilation...

I'm assuming that this bathroom has,a toilet.... So what's the point of the humid stat fan.... It can't detect smells!
 
The bathroom today for instance has just been refurbished/finished by a builder. Looks good! So I say ah well shame about the finish gotta fit a 3a fuse in the feed. Just Pull up your floorboards and screw up your lovely bathroom and charge you a fortune (I am reassuringly expensive), and you get another ugly switch into the bargain! Ok? lovely. No I don't think I should be playing twisters with the manufacturer! They should fit their own fuse into their own product. It is incomplete if it is not intrinsically safe. I imagine a lot of fan manufacturers after hearing about one of their fans catching fire thought Oh oh its suing time. And they just managed to squeak out of it by blaming the contractor, poor sod. So now instead of making their product safe, we have to cover for their shoddy production methods! Ok rant over.
And anyway the three pole isolator, I often find switched off as most people can't stand the noise so it does have a function after all.
 
Interesting discussion. The last bathroom fan I fitted I ran the whole lighting circuit via a SFCU with a 3A fuse. Only because the manufacturer listed this as a requirement in the installation instructions.
 
I do a bit of work fitting fans and LED downlights for a couple of bathroom fitters. Most situations see me adding a RCD SCFU for my bathroom install so the fan fuse pops in there.
 
A female electrician who sometimes works for me, and with Kate does not contribute much here as she feels it gets a bit too "controversial" (my word) sometimes.
 
I think it depends on what you are used to. This place is no worse than any other forums I've used in the past. There are some here who like to cause controversy but it's just a case of figuring out who they are quickly and making a judgement call as to whether what they are posting is designed to incite a flame war or not. If it is, just ignore them in that instance. Thus far, that list of people is pretty short partly I think because the vast majority of people on here are more mature by the very nature of what's being discussed, it's people in the trades, home owners etc. For many forums it's gaggles of screaming kids who have zero clue about how to conduct themselves in a mature way, especially when faced with differing opinions. Plus, I grew up in a male dominated family and I've studied and worked in male dominated industries my entire life, so having it out with a bunch of guys is something I'm used to doing, although I'm more used to it being around a pub table with a decent beer in hand.

I guess where it can get a bit fraught is when the regs result in a grey area and then it becomes peoples personal interpretations. A prime example is the thread that's been running about T+E in commercial. I have opinions on that but I chose to stay out of it (aside from liking the odd post here and there) because some people were just way to aggressive with their comments and it really did seem to become a series of personal vendettas because someone dared to have a differing opinion... I've been in the game 30 years, served my time blah blah blah... yeah great, but that doesn't automatically mean (a) you're right and (b) you're a decent spark. And I guess that is probably the biggest sticking point for me personally, there are some things I don't feel qualified to comment on, not because I don't have a view or because I've not encountered them, but because I'm not in a position to claim expert status because until you've got certain qualifications (NVQ, AM2 spring to mind), in the eyes of some people you can't possibly have a clue, regardless of what alternative experience you may have.

An extension of this is that there are some folks here who are willing to answer questions and treat people with respect (providing they conduct themselves in a mature, respectful way) even if (from their perspective) they may be dumb questions, then there are others who just... well, I don't know... in my last job I encountered someone who claimed to be amazing, qualified up to the hilt and he let everyone know it. Yet I was hardly ever able to get a sensible answer out of him about anything. Instead questions were met with derision and comments with an overwhelming air of "I can't believe you just asked me such a simple question... you're clearly clueless!". Then I started investigating his work and well it wasn't good and I found myself thinking "And you think you're superior to me why exactly???". This kind of superiority complex where you put people down is going to put people off, I've seen it demonstrated a couple of times here and it's certainly stopped me posting in one or two threads.

Anyhow, I would encourage the girls to get on and post :D Maybe we should have our own girls only forum??? :)
 
I always install a Click Scholmore fused TP&N isolator if the manufacture asks for 3 amp fuse.

That said, I've been to two failed bathroom extractor fans. One was filled with a wasp's nest, and the other was filled with bird nesting materials. Neither of the fans were fused, nor had they tripped the lighting circuit and there had been no fire or was there signs of thermal damage. ;)
 
It must happen (fire from bathroom extractor fan), but I've never seen it. I too install a 3A fuse where manuf. asks.

Sounds like @SparkyChick's work mate may have had figjam syndrome ? (Is that a common expression? - eff I'm great, just ask me)
 
Here's an idea. What about a 3A fuse in the neutral?
How many regs would that break.
 

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FCU for Extractor fan
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