On 22/05/2013 18:18, wrote:

I am considering fitting a mirror demisting pad behind the mirrored
glass door of the vanity cabinet above the sink in the bathroom. This
would get power from the light switch which is the pull cord type
located on the ceiling.

Your first obstacle is likely to be that the switch will only have live,
and and switched live wires, and no neutral. You would need to take the
feed from the light fitting itself.

Someone has said I need to have an RCD in the supply to the demister
as the vanity cabinet is 18" above the sink.

Ideally you would need a SELV heating pad that runs from a low voltage
supply. This can be derived from a transformer placed outside of the zones.

Two queries is I may....

1. Is the RCD really necessary? 2. If yes, then will an RCD need to
have an earth wire as the supply from the lighting circuit will be
live and neutral only.

Mains appliances in bathrooms really should have RCD protection. Using a
SELV appliance is a way round this.

If your lighting circuit lacks an earth, then it sounds as if RCD
protection for that circuit would be very strongly advised anyway. See:

http://wiki.diyfaq.org.uk/index.php?...thout_an_Earth



--
Cheers,

John.

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