Weird GFI problem - wired correctly but not tripping
 

I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...

Weird GFI problem - wired correctly but not tripping
 

blueman writes:

I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.
CORRECTION, when I hold down the test button the lights show:
off, yellow, red
which in a normal situation would be signalling a Hot/Neutral reverse
but is probably just an artifact of the test button shunting current.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...

Weird GFI problem - wired correctly but not tripping
 

In article on Thu, 23 Jul 2009
23:32:52 -0400, blueman wrote:

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?


Your GFIs, both old and new, are fine. On a GFI, the tester built-in to
the receptacle works by shunting some current from hot to neutral.

Your hand held tester works a little differently - it shunts some
current from hot to ground. Either there is a grounding problem on that
circuit, or the hand held tester itself is faulty.

--
Seth Goodman

Weird GFI problem - wired correctly but not tripping
 

"blueman" wrote in message
...
I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...


*Pull out the GFI and use a pigtail socket and bulb to confirm that you have
a functional ground.

Weird GFI problem - wired correctly but not tripping
 

On Jul 24, 9:36*am, "John Grabowski" wrote:
"blueman" wrote in message

...





I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. *But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...

*Pull out the GFI and use a pigtail socket and bulb to confirm that you have
a functional ground.- Hide quoted text -

- Show quoted text -

Suggestion/question?????.
GFIs trip when there is a certain amount of (milliamps) unbalance
between current flowing in the live and neutral conductors; true?
If the tester itself use say LEDs which take a very small amounts of
current maybe there is not enough (total) current flowing to unbalance
the GFI?
Not familiar with the circuit arrangement of the tester.
Or as suggested the ground is imperfect.

Weird GFI problem - wired correctly but not tripping
 

blueman wrote:
I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...
Hmm,
I'd measure Ohmage between ground and neutral with a meter on that
outlet. Reading should be very close to zero Ohm.

Weird GFI problem - wired correctly but not tripping
 

*Pull out the GFI and use a pigtail socket and bulb to confirm that you have
a functional ground.- Hide quoted text -

- Show quoted text -

A GFI's operation has nothing to do with the ground. It monitors the
current flowing throught the hot and neutral.

Weird GFI problem - wired correctly but not tripping
 

In article , Mike rock wrote:
*Pull out the GFI and use a pigtail socket and bulb to confirm that you have
a functional ground.


A GFI's operation has nothing to do with the ground. It monitors the
current flowing throught the hot and neutral.

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.

Weird GFI problem - wired correctly but not tripping
 

"John Grabowski" writes:

"blueman" wrote in message
...
I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...


*Pull out the GFI and use a pigtail socket and bulb to confirm that
you have a functional ground.

BINGO - no *functional* ground.

Though not clear why the gfi tester didn't read it as an open ground
unless there was some "inducted" current flow from ground to neutral
in the cable sheathing. Also, interestingly, a digital (not analog)
ohmeter read 120v between hot and ground again maybe consistent with
inducted current. But as always resistive loads (i.e. bulb on a
pigtail) tell the truth.

This all does make me worry though about the accuracy of the low-end
GFI tester I have -- i.e., how many open grounds are there lurking
somewhere in the house that the tester has failed to detect...

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.

Weird GFI problem - wired correctly but not tripping
 

blueman writes:

"John Grabowski" writes:

"blueman" wrote in message
...
I have a Leviton GFI in my bathroom which I happened to test today
with my little 3 prong/3 lamp tester. The socket shows as being wired
correctly (2 yellow lights, no red) but pressing the 'trip' button on
my tester failed to trip the GFI (note when the trip button is
depressed all 3 lights (yellow-yellow-red) light up on the tester).
The test button on the GFI works fine though.

Still figuring that something must be wrong with the GFI, I replaced
it with a new one. The physical wiring is correct and again the tester
shows it is wired correctly. Also, the little green LED on the GFI is
lit presumably showing it is working. But again the trip button failed to
trigger the GFI even though again the manual test button on the GFI
worked.

My GFI tester worked fine triggering the other 13 or so GFI's in my house.

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?

I am stumped...


*Pull out the GFI and use a pigtail socket and bulb to confirm that
you have a functional ground.

BINGO - no *functional* ground.

Though not clear why the gfi tester didn't read it as an open ground
unless there was some "inducted" current flow from ground to neutral
in the cable sheathing. Also, interestingly, a digital (not analog)
ohmeter read 120v between hot and ground again maybe consistent with
inducted current. But as always resistive loads (i.e. bulb on a
pigtail) tell the truth.

This all does make me worry though about the accuracy of the low-end
GFI tester I have -- i.e., how many open grounds are there lurking
somewhere in the house that the tester has failed to detect...

Actually it is kind of ironic that while the GFI tester didn't detect
a floating ground in its normal mode, it (indirectly) signalled a bad
ground by failing to trip the GFI when the test button was pressed.

Do better quality GFI testers do a better job of testing for
*functional* grounds?

Also this led me to experiment and I noticed that if the ground and
neutral pin on the GFI tester are both wired to neutral then the GFI
tests ok which in some ways is electrically understandable since
ultimately the neutral and hots are bonded at the service
entrance. However, it is not a code ground.

Do better quality GFI testers have a way of testing for functional
ground vs. neutral used as ground? (perhaps as a proxy they could
measure resistance between neutral and ground???)

Weird GFI problem - wired correctly but not tripping
 

Weird GFI problem - wired correctly but not tripping
 

On 2009-07-24, blueman wrote:

But how does the GFI test button work? Does it really just test if
the breaker works or does it have a way of testing that the current
monitoring part works?

The GFI uses a current transformer to detect a downstream imbalance
between hot and neutral current. The test button has access to the
hot and neutral both before and after this current transformer. So it
shunts a small amount of current from the hot after the transformer to
the neutral before the transformer (or vice versa, I don't know),
which creates an imbalance in the current transformer.

Cheers, Wayne

Weird GFI problem - wired correctly but not tripping
 

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.

Weird GFI problem - wired correctly but not tripping
 

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.

Weird GFI problem - wired correctly but not tripping
 

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.

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...

Weird GFI problem - wired correctly but not tripping
 

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

Weird GFI problem - wired correctly but not tripping
 

On Fri, 24 Jul 2009 05:24:09 -0400, Seth Goodman
wrote:

In article on Thu, 23 Jul 2009
23:32:52 -0400, blueman wrote:

Any idea what could be happening here?
Why would both the old and new GFI show as being wired correctly and
yet fail to trip?


Your GFIs, both old and new, are fine. On a GFI, the tester built-in to
the receptacle works by shunting some current from hot to neutral.

Less incompletely, hot on the LOAD side to neutral on the LINE side.

Your hand held tester works a little differently - it shunts some
current from hot to ground. Either there is a grounding problem on that
circuit, or the hand held tester itself is faulty.

Weird GFI problem - wired correctly but not tripping
 

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.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.


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...

Weird GFI problem - wired correctly but not tripping
 

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.

Weird GFI problem - wired correctly but not tripping
 

"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?

Weird GFI problem - wired correctly but not tripping
 

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.

Weird GFI problem - wired correctly but not tripping
 

On Sun, 26 Jul 2009 00:09:10 -0400, blueman wrote:

[snip]


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

If current is flowing through that neutral, some would be diverted to
ground. That would cause an imbalance through the GFCI, tripping it.

Weird GFI problem - wired correctly but not tripping
 

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.

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.)

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

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

Weird GFI problem - wired correctly but not tripping
 

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!

Weird GFI problem - wired correctly but not tripping