On 07 Jul 2005 20:48:55 GMT,it is alleged that
(Andrew Gabriel) spake thusly in uk.d-i-y:

45 amps will be generating some 10kW at the scene of the fault.
It would be pretty impossible to even deliberately engineer such
a fault which lasted more than a few seconds, without it either
shorting completely or blowing itself out into an open circuit.
The generation of 10kW will change the nature of a fault site
very quickly.

There just aren't credible scenarios where large currents flow
for an extended period in the earth conductor.

Fair point :-)

On a fully loaded US system, the neutral current is zero.
Same is true of a fully loaded 3-phase system in UK, which
is why 4-wire 3-phase circuits do sometimes have reduced
size neutrals (need to watch out for 3rd-harmonic components
though, which do add in the neutral rather than cancel out).

Yep, many people in the US are now being caught out by needing larger
size neutrals than phase conductors, especially in IT rich
environments such as office space etc, where the PC and IT equipment
PSUs generate nasty harmonics and cause local overheating of the
neutrals, not good.

--
I have left orders to be awakened at any time in case of national emergency,
even if I'm in a cabinet meeting.
- Ronald Reagan