Wanderer wrote in message ...
On Fri, 5 Sep 2003 20:49:41 +0100, Chris Oates wrote:
"Andy Dingley" wrote in message
...

Equipotential bonding is there so that no two metal objects can
develop a high voltage across them. This is typical from a high
impedance fault condition - maybe a heater with failing insulation,
not enough to cause an earth fault, but still enough to make the case
give you a shock. Humans are normally high impedance, so won't suffer
such shocks - but wet humans are much more conductive, so bonding
becomes especially important in bathrooms.

or to look at it another way....
(a)even more paths for across the chest shocks
(b)more things that can become live

you are not allowed bare protective conductors
but you can have acres of bonded metal

where I work bonding causes more problems than it solves
because it just increases the chance of electrucution


Err, are you suggesting that the Faraday Cage doesn't work? So how come
most leccy companies now do so much 'hands on' live working?


Hi.

A bathroom is not really like a faraday cage, since it has mains in
there that is not at the 'cage' potential. Its more like an earthed
cage with wired appliances in it, which occasionally become live.

2 issues with equipotential earthed bonding a

a) a shock from light fitting to bonded metalwork is worse than a
shock from light to unbonded metalwork
and
b) should there be a fault with the earth feed lots of metal will
become live instead of a little.

Those points dont make it bad, but they do make it less great than it
first looks.



But I would look at equipotential bonding from another point of
view...

How many lives has it saved? Our of 50 deaths per year from
electrocution in the UK, how many of those were bathroom
electrocutions? And how many of those would have been saved by
equipotential bonding?

Now, whats the cost of equipotentially bonding the nations bathrooms?
How much per life is that?

Now, people die en masse due to their own ignorance, eg due to stupid
eating habits. How much would a food education campaign cost? How many
lives would it save? How much per life is that? How many times the
number of lives would be saved with the same amount of money?


Regards, NT