I'm adding a combined low voltage light/fan to a shower cubicle.
I was going to put a dedicated cable to it from the CU, but it would be more practical to use the existing shower pull switch to turn on/off the fan/light whenever the shower unit is turned on.
Would this be allowable under the various regs? Or should I go with the original plan of a separate feed/MCB/switch for the fan/light?
Thanks Alan.
Fitting an RCD fused spur off the lighting circuit and supplying the b/room lights and fans, etc, would this preclude equipotential bonding in a bathroom in 17th edition of IEE regs. The fused spur RCDs are available from Screwfix.
Allowable - yes, in principle, if properly designed but rather impractical and not (IMHO) advisable. You would need to spur off from the 45 A pull switch in a short piece of 2.5 mm^2 cable to a fused connection unit and then fuse down to 5 A for 1 or 1.5 mm^2 cable to the fan unit. A design calculation (using the adiabatic equation) would be needed to be sure that the intermediate size cable is properly fault-protected by the shower circuit's fuse or MCB (probably 45 A). The unit containing the 5 A fuse would need to be reasonably accessible, i.e. not in the loft.
Much simpler to put it on the existing lighting circuit with its own switch. If you do it before 1st July you won't need to add an RCD for the bathroom lighting, but supplementary bonding may be required.
To comply with the 17th edition all circuits feeding bathroom equipment (including the shower) would need to be 30 mA RCD protected, not just the added fan unit.
Nothing precludes supplementary bonding in a bathroom, but its use is optional under the 17th ed. provided that RCD protection is in place as described above _and_ the premises have compliant main equipotential bonding.
Ha, I hadnt thought of adding to the existing light circuit, for some reason I thought it had to be separately protected. That is probably the easiest solution, as the light circuit cables are readily acessible in the loft, but with the slight downside of having to have 2 separate switches for fan and shower. Thanks Alan.
In my utility room the separate lights for loo and shower, and the fan which serves both are on one pull switch.
Isn't that what I said "supplying the b/room lights and fans, etc". If heavier load then off the ring, or back to the CU.
So no need as I said.
yep.
The term "reasonably accessible" seems to be a joke these days. I can get into most lofts faster than I can access a CU in a kitchen cupboard.
Adam
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