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.
--
To reply by e-mail, change the ' + ' to 'plus'.

"A.Lee" wrote in message
...
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?

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.

A.Lee wrote:
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?

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.

--
Andy

Doctor Drivel wrote:

Fitting an RCD fused spur off the lighting circuit and supplying the
b/room lights and fans, etc,

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.

would this preclude equipotential bonding in a bathroom in 17th
edition of IEE regs.

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.

--
Andy

Andy Wade wrote:

A.Lee wrote:
I'm adding a combined low voltage light/fan to a shower cubicle.

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.

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.
--
To reply by e-mail, change the ' + ' to 'plus'.

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.

In my utility room the separate lights for loo and shower, and the fan
which serves both are on one pull switch.

"Andy Wade" wrote in message
...
Doctor Drivel wrote:

Fitting an RCD fused spur off the lighting circuit and supplying the
b/room lights and fans, etc,

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.

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.

would this preclude equipotential bonding in a bathroom in 17th
edition of IEE regs.

Nothing precludes supplementary bonding in a bathroom, but its use is
optional under the 17th ed.

So no need as I said.

provided that RCD protection is in place as described above _and_ the
premises have compliant main equipotential bonding.

yep.

"Andy Wade" wrote in message
...
A.Lee wrote:
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?

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.


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