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Posted by Doug Miller on July 27, 2007, 10:57 pm
>>
>>
>>
>>
>> >> 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.
>>
>> >> Thanks
>>
>> > 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
>> > difference; trips.
>>
>> > I've installed GFI's in old houses w/o grounds (& applied the
>> > sticker) ......they trip just fine.
>>
>> > cheers
>> > Bob
>>
>> 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
>> installed in.
>>
>> 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,
>> Curt
>
>Curt-
>
>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.
Give that man a cigar.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
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