shower extractor fan and light

[bobp]

Help
In planning stage of new bathroom. Is it safe to wire a shower fan and light to the on/off pull switch that operates a 9.5 kw electric shower? The later will use 10mm cable with relevant RCD & MCB. I don't particularly want to operate the light/fan off the general light switch as this means the unit will come on regardless of whether the shower is in use or not.

 

[bernardgreen]

Help
Is it safe to wire a shower fan and light to the on/off pull switch that operates a 9.5 kw electric shower?

NO

[1] A 40 amp MCB protecting a lighting circuit

[2] even if you fuse down to 5 amp for the lighting circuit there WILL be a time when you need the light ON and the shower ISOLATED for some reason.

[3] If something goes wrong and the shower trips the RCD then the light goes out. Nasty if the RCD was tripped when an accident happened.

 

[bobp]

Many thanks, there will be other lights in the bathroom so no problem there. Are you saying that if I fit a 5 amp in line fuse it will be OK to connect to the shower ceiling switch?

 

[bernardgreen]

I am not sure about that as it depends if an FCU is allowable between a 40 amp circuit and a 5 amp circuit.

Can the FCU safely withstand a 40 amp internal fault on its input side (should its internals fail) in the time it takes for the 40 amp MCB to operate ? I don't know the answer to that.