> In the US power distribution system, I understand that the neutral is
> connected to ground at the point of entry to the property's distribution
> board. Do the electricity company provide a ground wire in parallel with
> the neutral, or is the ground purely a local ground from a ground rod or
> similar?
Utility companies mainly use one ground wire. It serve all functions,
including neutral to balance uneven loads. At periodic intervals, it is
grounded to earth grounds. That is at every transformer, switching,
power factor correction, or lightning arrestor and normally at points
where the span is especially exposed to lightning. If the poles are
metal, it is grounded at every pole. Sometimes guy lines are used
as part of this ground.
> Is their any fault detection on that ground connection so that a ruptured
> neutral won't lead to the return current being through that ground
> connection?
No. Except at on main transmission lines where phases are
always balanced unless there is a fault, like a wire down.
Distribution lines are protected only by fuses or electronic breakers
that limit overall current. Electronic breakers often are three strike
breakers, that reset twice automatically before requiring a manual
reset at the pole.
> Are cables witha metallic sheath used in the US, with the sheath being the
> neutral? Here we have cables with 3 phase conductors and a metal sheath
> for neutral - and ruptured neutrals aren't unknown.
No, unless the wire is buried or exposed to possible destructive
contact.
It's only INSIDE the building where ground fault detection occurs.
The distribution and circuit breaker box in the building is where the
neutral and safety ground are split.
73, Tom W8JI
w8ji@contesting.com
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