Sylvia Else wrote:

D Yuniskis wrote:

Sylvia Else wrote:

Phil Allison wrote:

The MEN system:

In Australia, AC power delivery uses a system called " Multiple
Earth Neutral " - which requires that the neutral conductors in a
premises be connected to the plumbing system at the distribution
board (ie power box). It also requires that an earth stake be
installed for the same purpose, but some older premises may not have
this.


If as you say, neutral has to be tied to Earth at the premises, then
I can indeed see that the situation might not be so bad.


Grounding the mains to "plumbing" *was* common in the US many
years ago. Now, I believe, you *must* ground to a metal
rod driven into the earth (8 ft?). Note that if the water
meter was removed, your earth-through-plumbing would fail.

On the face of it, having significant current flowing from neutral to
Earth would have to indicate a fault. It would be nice for the
breakers to trip in such a situation, but I can't see that they will.


This is how GFCI breakers work -- they watch for current "leaking"
off to ground someplace other than in the "return" conductor.


In the scenario I outlined, the currents in the live and neutral
conductors passing through the breakers would remain equal, so they
wouldn't trip.

What I need is something to detect current through the link between
neutral and ground, which would then disconnect both phases. Of course,
it could trip as the result of a fault with the neigbour's neutral wire,
but I could live with that.

Sylvia.
You need to pass the live and neutral through a common mode
transformer. when one leg gets shorted to ground, it unbalances.
You wrap another winding in that coil which will then produce some
current for you to trigger a protection device. The current will only
be present when the common mode becomes unbalanced due to them
canceling each other out under normal operation.

This will accommodate for both legs.

have a good day..