Bathroom fan wiring - question

[asifboda]

Hi

I know there are lots of threads about wiring bathroom fans and I have read them but wanted to double check something.

I am replacing a timer fan with a new Vent Axia timer fan with electric shutters. The Vent Axia fan requires a local 1 amp fuse. The other fan didn't require a local fuse when supplied off the lighting circuit.

The Vent Axia instructions show the fuse on the supply live before the light switch, so that both live and switched live are protected. The location of our wiring makes it very tricky to access the incoming supply to this circuit without a fair bit of decorative destruction. My options thererfore appeared to be put a fuse on both the live and switched live going into the isolator switch or buy a fan with electric shutters which doesn't need a local fuse. Re the latter, I found this Icon 15 fan where the wiring diagram shows the local fuse protecting only the permanent live cable (see

http://www.airflow.co.uk/faq/files/iCON_230V_Operating_Instructions_iss_L.pdf

I would have thought this leaves the switched live unprotected and therefore the fuse is sort of useless? Any thoughts guys? Because if this is viable, it makes my job easy. If not, then surprised it's being shown on the installation instructions for what looks like a decent fan?

Thanks

Asif

 

[bernardgreen]

The 1 amp fuse is almost always there to protect the lighting circuit from a shorted fan motor taking out the 6 amp MCB and putting all lights out. In a room with no windows for natural light a loss of electric light could create a major risk of accident.

It also limits the amount of power in the form of heat that would be created in a shorted motor.

In the majority of fans the switched live to the fan only feeds a high impedance voltage sensor so there is virtual no risk of an internal fan fault that takes a high fault current on the switched.

The voltage sensor controls the switch that connects the fan to the permanent live.

If there is a wiring fault that causes a fault current on the switched live then the MCB for the lighting will protect the system.

Edit to correct typing error

 

[kevindgas]

The Vent Axia fan requires a local 1 amp fuse. The other fan didn't require a local fuse when supplied off the lighting circuit.

can't see anything in the instructions about a 1 amp fuse can see that there is a 3 amp fuse in the perm live supply. the only thing i can suggest is a FCU with a 3 amp fuse.

 

[ban-all-sheds]

The location of our wiring makes it very tricky to access the incoming supply to this circuit without a fair bit of decorative destruction.

Where are you going to get the neutral from?

 

[asifboda]

Replies to above:

- the Vent Axia I have requires a 1amp fuse, the instructions i pasted the link to are for another fan
- neutral: the fan I am replacing was already wired in with a three core + earth running from a junction box that I cannot now access easily but which is on the (upstairs) lighting circuit, so I don't need to take a new neutral.

Re my original question, I have one reply suggesting that putting the local fuse only on the perm live and leaving the switched unprotected would be OK. Any more views?

Asif

 

[flameport]

If you really want a 1A fuse in the circuit, get one of these with a suitable fuse:
http://www.rapidonline.com/Electric...ine-fuseholder-250V-AC-white/80051/kw/26-1586
and fit inside the fan housing.

Or just connect the fan directly to the wiring, as is probably done in 99% of installations.