On Sun, 7 Nov 2004 23:23:28 -0000, "Sunbeam"
wrote:

This afternoon I turned off a switched fused spur supplying a 3kw water
heater and got a packet off the switch.
This is an MK dpdt thing with non-metallic front and pattress. Plastic for
want of a better word. Supply is from a 16A mcb via a 60A rccb.
All items and and cabling are new within the last 2 months.
All are located within an unheated outdoor, but waterproof, building.
Condensation may be a problem but there was no sign of any water in, on or
around the offending spur. I put a tester to the plastic casing and it
showed mains voltage over most of the surface.
Any ideas why I copped a packet and also why the rccb didn't trip?
Many thanks
Sunbeam


Hi,

Sounds like the there is a fault with the earthing of the switch. Is
there a plate behind the front which earths the two screw holes? If
this is floating it could allow some capacitative coupling or tracking
(through damp) of mains voltages.

If connected and there is a break in the earthing elsewhere then
capacitative coupling from live could allow it to float at a high
voltage, especially if the wiring is old.

If all the earthing of the switch and its supply is in order, it could
be defective plastic that can absorb water through being porous. Try a
different make switch so to be sure it is not from the same batch as
the original.

cheers,
Pete.