"Sbharris[atsign]ix.netcom.com" wrote in
oups.com:

A GFCI works, in part, as you describe below.
In addition, it detects a ground/neutral short
as described at the following url:
http://www.codecheck.com/gfci_*principal.htm
I believe that function is what the poster was
referring to.

Correct. Modern GFI's really have two parts. The main one keeps you
from killing yourself, by cutting off current when you have a hot to
ground current. The active SECOND part (a second toroid) allows the
device to detect ground-neutral faults, so it can trip then, when its
sensing function has been compromised.

Look again. See the two wires going through the core? [ignore the test
line]

Each of those wires serves as the primary of a transformer.

As long as the SAME current flows in BOTH of those wires, they cancel each
other out. No current is induced into the secondary.

An imbalance in the current in those wires can be due to MORE current
flowing in EITHER of them than in the other.

An imbalance will trip the GFI.

Notice, there is NO second circuit to detect ground/neutral shorts. It is
an imbalance in current that trips the GFI.

The GFI depends on the current through BOTH wires being equal.




--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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