Dorothy - I feel as if I am banging my head against a wall and I'm sure
person to person we would amicably reach agreed territory (perhaps some
of this is misinterpretation)
I disagree with your arguments - especially where coffee will now
conduct so much available current on the chassis and conversely, earth
impedance of an extra extension will not take the current???? - what one
in a million nonsense!
Lets look at an example where the earth of a premises is 0.5 ohms (which
is probably far from reality). Over here I could achieve a theoretical
current of 480A (I guess that is 240A over there). Now, if you extension
lead added another 0.5 ohm which is very unlikely (it is far more likely
the overused wall socket has a more worn and unreliable earth than the
extension), you will still have 240A over here (and 120A over there). To
drop it to 40A the earth would need an impedance of 6 ohms (3ohm in the
US) and if it was that high there would be inherent H&S risks in the
buildings wiring. That is NOT going to be as a result of a bloody
extension lead - or two or three.
to just retain our different opinions then Dorothy.
Any which way - any place who doesn't use a RCCB (ELCB whatever) is
mad. Very few places run without one. Doesn't much matter about the
arguable earth issue then really
Whatever you choose to call them - current imbalance devices are an
excellent idea. Provided the fault current goes to earth. They don't
Take the case above of the fan heater. This time it is double
insulated, no earth connection. In goes the coffee. The coffee short
circuits the live to neutral. The current imbalance device does not
trip - the currents are still balanced. The only protection now is the
fuse. But the fault current is limited by the loop impedance - and one
of those wiping contacts has a couple of ohms resistance. Result - 3kW
dissipating in that wiping contact for the next 10 seconds or more.
As you say, we'll just have to retain our different opinions. There
isn't much point going over the same ground (joke) time after time.
We can leave it to others to form their own opinions..
I am equally concerned about your explanation of the current imbalance
They do NOT measure leakage on the earth - and in fact operate the same
without any earth.
They purely rely on a current imbalance between L and N.
Naturally, a leak to earth will achieve this but this effect is not
exclusive to this as it is measured on the L/N imbalance.