Bathroom fan, 3 pole isolation or fused spur?

[Penance]

Just picked up a timed fan and 3 pole switch. Fan is 4" 20 watt. I was going to run 3 core and earth from 3 plate light via 3 pole switch and to fan as per normal.
Just read manufacturers instructions and it says must be a double pole fused (3 amp) spur. Can't see the logic to that.

What would you guys do?
I know it's maybe a daft question but this will be part of my assessment.

 

[Des 56]

Manufacturers instructions should be followed
It would cost them to put one in the fan, so they put it in the instructions instead,its cheaper

6 amp mcb and 3 amp fuse will do battle to see which would go first,so probable waste of time

Anyway,if you insist on using a light to operate a fan (I personally never ever do so )then what you could do is use the switched fused spur to supply the light and your 3 pole islostor for the fan off the light as you descibed

 

[telectrix]

Des, how do you do it then?

 

[Penance]

Des, it's a small downstairs bog with no window so as far as I'm aware it needs a timed extractor that operates when the room is used. So a fan run from the light seems the obvious solution no?
Interested in how you'd do it.

So then, I should put in a dp fcu then?
If so should I go light > fcu > fan or would you put the 3 pole switch between fcu and fan?

 

[Des 56]

Seperate pull cord tucked away in the corner
My veiw is who wants a ventilation unit vibrating the rafters in the middle of the night when all they wanted to do was have a quick leak

 

[telectrix]

but which feed to the fan do you fuse at 3A? the permanent or the switched or both. only way to do both is to fuse the permanent line to the light.

 

[Penance]

See your point and it makes sense but don't the building regs say it needs to be auto?

 

[telectrix]

why. what happens when you go for a dump in the day, and don't switch the light on?

 

[Penance]

Tel, that was what I thought too, one fuse and two lines so do I ---- a coin.

No window in the room so even a daytime download would need the light on unless you wipe in brail!

Instructions are pretty generic to all fan models and I wonder if the dp fcu should only apply to the 2 wire switched fan?

 

[pennywise]

You can get time delayed fans that come on after a couple of minutes, so if your just popping in and out they don't activate but when activated they act like a standard timer fan.

 

[Des 56]

but which feed to the fan do you fuse at 3A? the permanent or the switched or both. only way to do both is to fuse the permanent line to the light.

Feed the swiched fused spur 3 amp to load side
From the load side,feed the fan permant live,from the load side also, feed the pull cord
The pull cord will manually switch the fan and switching it off will set the timer in motion

All connections made in the S/f spur

 

[SimpleSimon]

Are the instructions generic for the dp fans too?

 

[Penance]

Are the instructions generic for the dp fans too?

Seem to be yes. Individual internal diagrams but generic supplies.

 

[telectrix]

Feed the swiched fused spur 3 amp to load side
From the load side,feed the fan permant live,from the load side also, feed the pull cord
The pull cord will manually switch the fan and switching it off will set the timer in motion

All connections made in the S/f spur

that's fine des, as long as you're not feeding switched live from the light.