On Jul 26, 12:09 am, blueman wrote:
"John Grabowski" writes:
I fixed the problem by tracing upstream where I found that
the ground
wire had broken off in the box. Problem solved & thanks for
the help.

Thanks for posting the outcome. A broken ground; glad the OP found it.

BTW: I agree with the person who posted;
Quote: "If you'd read the entire thread, you would have seen that the
OP stated that
the GFCI trips normally when he presses the test button on the GFCI,
but fails
to trip when he presses the test button on his plug-in tester -- and
you would
have also seen an explanation of why this is so: the plug-in tester
shunts
current to *ground*, and *cannot* trip the GFCI unless there is a
functional
ground at the outlet.".

It seemed obvious the question was why didn't the 'test' feature of
the 'tester' work as expected!

Interesting thread and as often makes one think (and learn!). Thanks
for posting the original question.

Your welcome
And I learned a lot too -- it is always sobering to learn the
limitations of your test equipment (or any other limitations).

I wonder how many professionals (e.g., electricians, home inspectors,
city inspectors) let alone DIY'ers realize that:

1. A GFI tester can show the circuit being fine even though there is
no functional ground. Similarly a (digital) multimeter can read the
full 120V hot-to-ground. Both presumably due to induced currents.

2. The test button on a GFI can work also without a functional ground.

It all makes sense retrospectively, but probably not something that
most people think about...

*I usually use my Wiggly to test a GFI.

You must have either a very thin wiggly or special wide 'hot' slots

It will trip between hot and
ground. Using a wire to short between neutral and ground will also
trip the GFI.

Why would a short between neutral and ground cause the GFI to trip?

Because the GFI is comparing the currents flowing in the hot and
neutral. When you short the neutral to the ground, some of that
current goes to the ground instead of the neutral, so the current in
the hot and neutral becomes unequal.

The next logical question would be "But what if there is no load, so
no neutral current?" The GFI will still trip, because it constantly
injects a small test current itself to detect that situation.