Wiring an extractor fan into a bathroom lighting circuit.

[BigJake24]

Hi All

I have a Vent Axia va100svxt 12. The wiring diagram says the live coming into the ceiling junction must have a 3 amp fuse on it. I may be revealing my ignorance here but how can you put a 3 amp fuse into a lighting circuit. In a mains circuit it would be a fused spur but how does that work on a lighting circuit?

Amy help would be really appreciated.

 

[EdwardCurrent]

Hello Jake.
Is this fan to be installed in a bath/shower room or kitchen ? If so it becomes 'notifiable' work and in my opinion it would be in your interest to get a registered electrician to fit the fan, due to 'rules and regs' I'm afraid.

If not, is the circuit that you intend to use RCD protected ?

Regards
Ed.

 

[GaryMo]

Fused Spur Units aren't just exclusive to ring final circuits.

 

[Taylortwocities]

In a mains circuit it would be a fused spur but how does that work on a lighting circuit?

.

I think you may be a bit confused here. The old term "mains" referred to the supply voltage at 230/240volts. On that basis, all of the circuits coming from your fuseboard/consumer's unit are mains circuits. Mains voltage is still used as a gneralisation but it is not defined as a proper term.

Maybe you mean a ring final circuit? As noted above, you could use an FCU on any circuit, including radials and ring finals.

 

[Chri5]

In a mains circuit it would be a fused spur but how does that work on a lighting circuit?

A fused spur limits the maximum rating of the fuse you put in it.

So fuse at 1,3, 5, 7 amp etc.

With a lighting circuit, the main fuse at the board will be a 6 amp, so if you were silly enough to have a 13 amp fuse spur on a 6 amp light circuit under 'fan fault' conditions the board will pop and you will fall down the stairs in the darkness

So by having a fuse spur rating at 3 amp, if the fan goes faulty it would trip the fuse in the spur, and not knock out the lights on the same circuit.
Also it limits the fault tolerance since a 3 amp fuse will trip before a 6 amp,

If you check your fan rating, it's only likely to be in the region of 50-100 watts. Say 75w

So with the math being that amp = watts divide by volts 75w / 230v is about 0.3 amps use. Put a 1 amp fuse in if you want.

 

[ban-all-sheds]

a 3 amp fuse will trip before a 6 amp.

Hmmmmmmmm

 

[Taylortwocities]

A useful document here: http://www.beamainstallation.org.uk/assets/pdfs/SwitchFusegearDevices.pdf

Page 21 has good info re discrimination. Hmmm indeed!