Just spent the last two hours trying to figure out why the GFCI my
electrician installed in my new building doesn't trip correctly (that
includes at trip to the shop to get a new GFCI). I found out that the box
it is using as a ground isn't grounded. Another box 2 feet away is grounded
just fine and the GFCI housed by it trips under all tests.
What do electricians do in this case ? There's conduit to the box and I'm
wondering why it wouldn't be grounded in the first place. I'm thinking of
pulling a third copper wire and using that to ground the outlet but that
probably isn't the best solution.
If, as it sounds, you're talking a metal box and conduit, it should be
grounded. About the only way it can't be if the box feeding it is is if
the conduit isn't continuous or there was a plastic fitting used
somewhere. My first preference would be to fix the conduit rather than
pull another ground.
There must be something else going on.
A GFI will trip even if not grounded properly. That's why the GFI
comes with stickers that say "no equipment ground".
A GFI compares the hot current to the neutral current & based on a
I've installed GFI's in old houses w/o grounds (& applied the
sticker) ......they trip just fine.
The GFCI trips just fine when using it's self test button. It doesn't trip
when using the GFCI test button on the small outlet tester I am using. All
other (10 or so) GFCI outlets in the building trip when using the tester on
them but some of them didn't before I grounded them to the boxes they are
The tester has three lights on it - 2 yellow and one red and when an outlet
is well grounded to the box the 2 yellow lights are bright and the red one
is completely off. When an outlet doesn't seem to be grounded the two
yellow lights are lit but not too brighly and the red one glows a bit. The
instructions that came with the tester don't address what that means. I am
assuming that something is not right.
So, after doing everything possible to ground the GFCI to it's box I then
used a meter to measure the voltage difference between the hot lead and the
box. The voltage measured only 60V whereas a different, working box
measured 120V. That's why I assumed the box is not grounded.
Finally, I just hanged a copper wire from the ground screw of the
non-working GFCI to a good box and it then trips correctly.
Thanks the responses,
Good description of the situation.
Here's what I think may be happening..........
Your GFI tester works by generating a "true ground fault"....that is,
a small current leak to ground to simulate a problem (like you or
someone using power from the GFI about to get shocked).
So your tester cannot do this IF a ground does not exist.
I'm thinking that the GFI is fine but the method of test used by the
tester cannot work without a ground local to the GFI receptacle.
Other way to test the GFI is to get someone to stand bare foot on a
wet surface & stick a paper clip into the hot of the
GFI................j/k don't do this. :)
So, you're saying that the GFCI is probably working just fine and I can
ignore the results from the handheld tester? If that's what you are saying
then I think you are right but man, what good is this tester then ?
Possibly it is working 'correctly', that is as designed. There is no
promise it is going to provide protection
Only at your own risk.
See above! <g> The tester serves a useful purpose, you discovered
IMHO, and hell, I'm an idiot (but I do have an EE degree), one should
*NEVER* rely on conduit to provide ground paths. A seperate ground
wire must be installed. Relying on conduit to provide grounds leads to
floating boxes, outlets, GFI's that don't work, ARC fault interrupters
that don't work, and other strange and sometimes dangerous situations.
Pull a ground between the two boxes... But then again, I'm just a guy
on the Internet, so what do I know?
promise it is going to provide protection <<<<<
Do you mean it could be working as designed but provide no protection?
Correct me if I'm wrong but I was under the impression that a GFI
(that's what they were called when first introduced & what I still
call them) compares hot current to neutral current & trips based on
the presence of a small (ma) current delta.
Like I posted, the GFI's come with stickers that say "no equipment
Of course, a grounded box & grounded GFI are the best of all worlds
but unless there is a reason not to.......a GFI in an ungrounded box
is far superior a standard receptacle in an ungrounded box.
In my previous posts I was trying make sense of what was happening
hence the comment "probably ok", I was hoping that someone would jump
in and clarify the situation, having encountered similar.
Thanks for your interest in my problem. I learned alot from this thread.
To solve my problem I grounded the box. I know that I probably didn't need
it for the GFCI to work but I wanted to err on the side of safety.
The authors of the National Electrical Code do not agree.
Not if the conduit is installed properly.
It certainly does no harm to pull a ground, and there's no doubt that doing
so makes a better, more reliable installation. But it isn't necessary, and
it's not enough better than properly installed conduit to warrant the extra
Doug Miller (alphageek at milmac dot com)
conduits installed with shoddy workmanship, in high moisture/corrosive
environments, with gaps (!!!) in the middle, and all sorts of bad
I'm perhaps a bit conservative, I don't use (or allow to be used on
work that I'm involved in) push on terminals either--must use the
I really think the original post really reinforced my feelings: the
conduit wasn't making a good ground path between the boxes. Wire is
cheap, but one's life and the lives of others is not, so I always
insist on a pulled ground wire in these cases.
but, thanks for your comments! <g>
Unfortunately not everyone takes enough pride in his work to get the job done
right, and done right the first time.
I heartily agree with that.
But the GFCI will operate correctly even if there is no ground at all; they
simply don't need one. They operate by sensing a difference in the currents on
the hot and neutral conductors. If the current going out is not the same as
the current returning, it must be leaking somewhere, and so the device trips.
Doug Miller (alphageek at milmac dot com)
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