In article , David Maynard
writes

You mean a separate earth.

I do, yes.

Neutral is, of course, earthed.

This is the distinction made in the wiring code between the "grounded"
and the "grounding" terminal... which causes confusion all of its own


No, they expect an earth ground too.

I've been over this with w_tom at considerable length in the past (feel
free to have a google.) Because American electrical outlets can't be
guaranteed to have an earth terminal (for example, in older construction
as you point out), the makers of surge protectors for the American
market have to wire them to the lowest common denominator, so that a
surge on phase is shunted to neutral using one MOV.

In the UK and Europe, two MOVs are used - one to shunt phase to earth,
and another to shunt neutral to earth. This makes surge protectors made
for this market much more effective.

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