"blackboab" wrote in message
oups.com...
Sparks

if the live wire comes loose and touches the metal case
of my toaster then the current flows from the generator down the live
wire , through the metal case, through the earth wire to ground,
through the ground back to the generator where it goes up the earth
wire there to neutral ?

That's right - but as there isnt much resistance in this circuit, lots and
lots of current flows (as it is effectivly a short circuit) so the fuse or
circuit breaker will brlow/trip

when the neutral wire touches the metal case is the circuit simply
totally grounded with the neutral wire at the same potential as the
ground to which its connected ?

yes - if you dont have an RCD, then this fault will remain undetected, but
as long as the earth is all connected properly, then the toaster will still
finction and you shouldnt get a shock.

If you did not have an RCD, and you connected somthing to Live and Earth,
the appliace should work and nothing should blow or trip

If the circuit has an RCD, then some of the current will return via the
nutral wire, but some will return through the earth. The RCD will see that
there is an inbalance between the current flowing from the live and
returning via the nutral (It doesnt care where it has gone, it just knows it
is missing!), and it will trip.
Sockets will usually have a 30mA RCD - this will trip if the inbalanace is
30mA or greater.

This means, if there was a fault with your toaster where either the live or
the neutral was in contact with the metal casing, but the earth wire was not
connected, if you touch the metal casing, some current will be conducted
through you to earth - the RCD will spot this missing current, and trip,
hopefully saving your life :-)

Sparks...