[Amps] Safety grounding - was Mains Isolation Transformer

[Jim Smith]

> Lou said:
> > 3 insulated wires would be #6 and the bare bond wire would be #`10.<
> This is an interesting one. Is it assumed that you can't get a fault such
> that the full fault current flows down the ground (i.e. the protection)
> wire? Such fault current being greater than the normal load current?
> Intuitively, I'd sort of expect the protective ground conductor to be of
> at least the same gauge, if not bigger, than the  current carrying
> conductors.

All circuit breaker manufacturers publish trip curves for each of their
circuit breakers. This is a plot of time versus current required to trip the
circuit breaker. The higher the fault current, the faster the magnetic
sensor of a thermal/magnetic circuit breaker will act. These are used in
coordination studies to compare with other devices in the system as well as
equipment that can be damaged by overcurrent. The wire itself has a damage
curve that can be plotted on the same graph. If properly sized, the
equipment ground will be on the "safe" side of the trip curve.

Jim Smith,
KQ6UV