Shower extractor/light unit wiring problem

[elbowgrease]

Sorry about the mistake there. The 2.5mm2 cable is in reality a 6mm2 cable. I started from a different drawing and missed that one. I found that three 6 mm2 cables fit into a 45A ceiling mounted pull cord switch with neon and mechanical indicator OK with a deep surface box. Perhaps not the most attractive solution though.

Regarding the suggested MK box and contactor. I can see that this is a solution and it could be accommodated relatively discreetly in my particular instance but it seems a bit brutal for a crummy little fan and light.

If one were to use a suitably rated 240V AC normally open relay it sounds as though I still need to retain the second FCU fitted with a low rated fuse to supply it.

 

[plugwash]

"probably best" is a gross understatement, you MUST since when a fault occurs which will go first the 6mm cable or the 2.5 mm cable, not rocket science is it? the 2. 5 will heat up and cause a FIRE

what kind of fault were you thinking of

the possibility of overload is prevented by the fact that it is hard wired to a fixed current load

a short cuircuit will be disconnected by the mcb long before either cable is disconnected

also since his first diagram of what he initially did has 3x6mm in the isolator its obvious that he has managed to fit them in the terminals in shower isolators are quite generous so i can't imagine you couldn't fit 2x6mm in one side yes it would be a sqeeze but not impossible

 

[breezer]

short circuit, the 2.5 can not carry the same current as the 6mm (obvioulsy) so it should glow red burning its isulation then setting any surounding material on fire, the mcb will nt trip because current drawn is less tha it is rated for

 

[plugwash]

short cuircuit:

an extremely high current flows
the mcb fast trips
the cables never get a chance to get extremely hot

 

[breezer]

that is true in theory, doesnt always work in practice, i have seen it done / happen