Fusing Fans to manufacturers spec

[nickblake]

Well chaps ive been looking at the manufacturer requirements for fusing down fans ,an every one appears to require only the permernant live to be fused so having words with those nice people at scolmore click you can do it easily with the grid range that doesnt actually look like grid fuse and an isolator in the same switch brilliant thats what i say good old Click scholmore

 

[Strima]

To be safe I think I'll start fusing the whole bathroom lighting at 3a then no-one can send me to jail for anything...

That's the easiest option. With the vast majority made in China and with **** poor installation instructions it's hard at times to work out what they want.

 

[Lucas]

I must be the only person that doesn't put it through a switch fuse. Might be manufactors instructions but I don't see the point

 

[Octopus]

I must be the only person that doesn't put it through a switch fuse. Might be manufactors instructions but I don't see the point

Just don't show a fan installation at your next assessment,

Are you one of those who doesn't bother with cooker isolation, or shower isolation either?

 

[tank]

To be safe I think I'll start fusing the whole bathroom lighting at 3a then no-one can send me to jail for anything...

isn't that what we'd be doing by wiring as per fig 4 post 24? do people really wire fans this way? when the fan is isolated, so is the feed to the light? isolator and fuse after the ceiling rose, surely

 

[Richard Burns]

Whilst I agree that the fuse is fairly pointless since the circuit is protected by a 6A breaker (fires notwithstanding) since most manufacturers state the fuse should be before the light this is what I would tend to do.

If you only fuse the permanent line going to the fan then if the fuse goes you can still supply a line to the fan (that may now be in a dangerous state if it has overheated or such) by switching on the light. I do not know if the SL is just an electronic run signal to employ the PL or if the two lines are commoned up in the fan, but if it is the latter then you could be trying to operate the fan once it has blown the fuse and presumably cause the fire that was averted by the fuse blowing, or trip the 6A lighting if it is a more direct fault. If the former then there can still be a line supplied to a damaged circuit board which cannot be good.

e.g. with just PL fused: switch on bathroom light, fan starts, switch off bathroom light, fan overrun continues, you leave, five minutes later fuse goes, later you come back, switch on bathroom light, fan bursts into flames or all the lights go out.

With supply fused: switch on bathroom light, fan starts, switch off bathroom light, fan overrun continues, you leave, five minutes later fuse goes, later you come back, switch on bathroom light, no light, oh dear something has gone wrong, better find out what it is.

I think the two options are as shown in this borrowed and modified diagram and I would definitely prefer my fuses to isolate the whole supply and not just one leg of it.

Good

Bad
(in my opinion)

 

[Amp David]

All combos can be acheived by using the grid switch setup, so don't see the problems.

Fitted one yesterday and had the fan on a separate switch to the lighting, fitted along with a fuse module.

So it was a 3 gang plate with a fuse module - switch for fan - switch for lighting, then 3 pole iso in loft local to the fan.

Jobs a good un

 

[yellowvanman]

that won't work with a timed fan, you need both perm and switched.

That's what I was trying to say!

 

[telectrix]

Whilst I agree that the fuse is fairly pointless since the circuit is protected by a 6A breaker (fires notwithstanding) since most manufacturers state the fuse should be before the light this is what I would tend to do.

If you only fuse the permanent line going to the fan then if the fuse goes you can still supply a line to the fan (that may now be in a dangerous state if it has overheated or such) by switching on the light. I do not know if the SL is just an electronic run signal to employ the PL or if the two lines are commoned up in the fan, but if it is the latter then you could be trying to operate the fan once it has blown the fuse and presumably cause the fire that was averted by the fuse blowing, or trip the 6A lighting if it is a more direct fault. If the former then there can still be a line supplied to a damaged circuit board which cannot be good.

e.g. with just PL fused: switch on bathroom light, fan starts, switch off bathroom light, fan overrun continues, you leave, five minutes later fuse goes, later you come back, switch on bathroom light, fan bursts into flames or all the lights go out.

With supply fused: switch on bathroom light, fan starts, switch off bathroom light, fan overrun continues, you leave, five minutes later fuse goes, later you come back, switch on bathroom light, no light, oh dear something has gone wrong, better find out what it is.

I think the two options are as shown in this borrowed and modified diagram and I would definitely prefer my fuses to isolate the whole supply and not just one leg of it.

Good
View attachment 14251
Bad
(in my opinion)

with that diagram, you switch off the D/P isolator to work on/replace the fan, but you're working in the dark , as the light is fed through the isolator.

 

[kingeri]

The way I am thinking is similar to the top diagram but with a triple pole isolator before the fan instead of the DP one at the start. OK, the lights will be off if the single fuse blows, but at least the homeowner will know something's up. But the fan can be isolated without isolating the lights as well.

 

[Richard Burns]

The diagram was taken from a manufacturers leaflet and they do not require the triple pole isolator but they do require a DP isolator at "source", the TP isolator is a guide to the building regs recommendation so is not shown on the diagram. To comply with all suggestions there would also be a TP isolator on the three live conductors going into the fan.
If the customer allows me to that is how I wire extract fans: DPSFCU, Light switch, TP isolator, fan.
Amp Davids suggestion is also valid since the fuse is still before both line and permanent line, however you cannot have a timed overrun based on the light switch in that case. The only way to do that is to take the supply to the click unit from the light switch and this then means there is no local DP isolator, however the CU main switch would cover that (not what they intend but would meet the instructions and any way why does a light require a DP isolator so the 3P isolator for the fan could be considered over and above the manufacturers instructions).

 

[Lucas]

NAPIT have never complained.

Never ever have I put an isolator in for anything, MCB's are there for a reason.

 

[nickblake]

yes mcb's are there for a reason for over load and fault protection , so no isolators for showers cookers ,

the fan timer circuit only requires the perm live to be fused as the switch live goes into the circuit componets which is basically a transistor that when the SL is operated switches the transistor on which operates the timer circuitory ,but the timer circuitory is fed via the permernant live hence only the permernant live is required to be fused as without the rest of the circuitory operating the switch live will basically only operate to the collector of the transistor and go no where else bit like sticking a termal block on a wire

 

[Marvo]

I read earlier in this thread that the reason for the requirement to fuse a bathroom fan was because of fires that occurred with them in the past.

How effective is a 3 Amp fuse on a device that draws possibly 30watts as a fire prevention measure? The fuse is rated at around 20 times the normal operating current. Maybe I'm missing something obvious.

 

[theleshollis]

I received the ELECSA "Spark" newsletter today with an article on fusing fans. So I thought I'd drag this back up. By coincidence I was talking to my mate about lighting circuits today. We were fitting some 3W LED lights. With all the incredibly low energy lighting we use nowadays surely rating a lighting point at 100W is ridiculous and we could start fitting 3A MCBs (if available) for lighting circuits. Then everybody would be happy.
Wouldn't they?