jeff_wisnia writes:

blueman wrote:
jeff_wisnia writes:

blueman wrote:

stan writes:



On Jul 24, 4:01 pm, "Stormin Mormon"
wrote:


Much safer, now. Good job.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
.

"blueman" wrote in message

...

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.

I don't think that "induced" is quite the proper term to use for
what's happening there. "Current flow through capacitive reactance"
would be more correct.


Can you explain what that means...

I guiess I was (mistakenly?) thinking that it was just basic E&M where
an alternating current in one wire induces a similar current in an
adjacent wire.

No, that's electromagnetic induction, and while it too can cause ****s
and grins for the uninitiated, that's not what makes electronic test
meters show significant AC voltages where there "shouldn't be any".

As I learned it, any two unconnected conductive bodies in the entire
universe have a capacitance between them which increases as the
spacing between them decreases.

If one conductor in a length of Romex isn't connected to anything (at
both ends) a capacitor is created, with the wires in that Romex being
the "plates" and the wire insulation the "dielectric". There exists a
(measureable) capacitance between the "open" wire and the other
wire(s) in that Romex, and that capacitance's value will be linearly
proportional to the length of the Romex.
Sure because capacitance is proportional to plate size which in this
case is proportional to length.

Capacitors can "conduct" AC current, and that conductive property is
called "reactance" and its units are in ohms. So in a very crude and
overly simplistic sense a capacitor can be viewed as an "AC resistor"
(whose resistance will vary inversely with the AC frequency.)

Ah yes - brings back memory of my college circuits course with Laplace
transforms and Z = - i * 1/2pi*f*C (or something like that...)

So, a very sensitive AC meter (like a digital electronic one), which
needs only a minute amount of current to make display a reading, will
often find that a disconnected wire can provide a path for that
current to some other wire through its capacitive reactance, and
possibly cause a meter reading.

This article explains capacitive reactance better than I ever could:

http://www.electronics-tutorials.ws/.../filter_1.html

Thanks!