"David Hansen" wrote in message
...
The fact that
two electric showers are installed when the supply fuse is only 60A and the meter
is
only 40A does not inspire confidence.

That depends on the assessed maximum demand and diversity, but it is
certainly not ideal. Do you have an overhead line or cable supplying
the house?

A cable. The main earth terminal is a clamp around the incoming cable - so if I've
understood the FAQ correctly it's a TN-S system.

Is bonding the copper pipe just as it enters the shower sufficient, or should the
bonding be attached to the actual shower metalwork/earth terminal?

That depends:-)

With bonding one needs to understand what is required and what is
not. People not understanding come up with horrors from time to
time; such as metal window frames, radiators and the metal in a sink
strainer all being bonded with little green and yellow wires that
will soon be broken off. Fortunately such things are pointless
anyway.

Bonding metal window frames can be dangerous AIUI, as a fault could electrocute a
window cleaner outside.

Radiators surely need bonding? (assuming the resistance to earth is less than 50
kOhms).

If pipes are made out of metal and there is reliable metal to metal
contact between pipes and fittings then little is gained by bonding.
The pipes and fittings are more conductive than any bonding cable
one will see in a house anyway.

Exactly. I'd have thought a test would be to measure the impedance between metal
objects which are connected via pipes, and if this is greater than a certain value
bonding is required. After all bonding simply reduces that impedance. Obviously this
would need to be redone after any plumbing work is carried out.

What am I missing here?

--
Andy