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???)