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I recently bought a house and am testing the GFCI outlets throughout the home to confirm they are working properly. All of the outlets work when the receptacle TEST button is pressed. However I also tested them with the Commercial Electric GFCI outlet tester (link below), and this is where I get confused.

In summary, the outlet tester will trip some GFCI outlets, but not all of them. For instance, I have identified that the outlets in the kitchen are on one of two circuits, and there are two GFCI outlets in the kitchen. As mentioned above, the TEST buttons work. One of the circuits will trip with the tester as well: I plug the tester in, push the button, the GFCI kicks in immediately, and there is no more power at the outlet. When I try the tester on a receptacle on the other circuit no trip occurs.

The tester instructions do say to hold the button for six seconds, which I tried to no effect. However, the circuit that does trip, does so nearly immediately.

For what it is worth I have only used the tester on the GFCI receptacles themselves at this point. I have not tried to use the tester on GFCI protected outlets that are downstream of the GFCI receptacle.

So I think I have a few questions based upon my experience:

  1. If the TEST button trips the GFCI, is the GFCI working? No exceptions?
  2. What would cause a GFCI outlet to trip with the TEST button, but not with the outlet tester?
  3. What does the GFCI outlet tester does to test the receptacle? How about the TEST button on the receptacle?

Thanks everyone!

Link to the tester used:

http://www.homedepot.com/p/Commercial-Electric-Tools-GFCI-Outlet-Tester-Green-MS102H/206029151

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    If your GFCI is missing a ground connection, it's TEST button will work, but a plug-in tester will not. – brhans Aug 24 '17 at 21:00
  • @haddsom You probably should check-out this short article which is about pre-2006 GFCI outlets failing after about 10 years. Testing GFCI Outlets familyhandyman.com/electrical/wiring-outlets/… – LongOfTooth Jul 16 '18 at 1:05
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Grounded circuit (green/bare ground wire wired properly):

  • Push "Test" on the GFCI protective device, and it trips -> PASS
  • Push "Test" on the GFCI protective device, and it does not trip -> FAIL
  • Push "Test" on a plug-in GFCI tester, and it trips -> PASS
  • Push "Test" on a plug-in GFCI tester, and it does not trip -> FAIL

A fail here indicates the GFCI unit is probably defective.

Ungrounded circuit (green/bare absent or defective):

  • Push "Test" on the GFCI protective device, and it trips -> PASS
  • Push "Test" on the GFCI protective device, and it does not trip -> FAIL
  • Push "Test" on a plug-in GFCI tester, and it trips -> FAIL FAIL FAIL
  • Push "Test" on a plug-in GFCI tester at the GFCI receptacle, and it does not trip -> PASS
  • Push "Test" on a plug-in GFCI tester at a downstream protected outlet, and it does not trip -> MEANINGLESS

Fail at the GFCI device probably indicates it is defective.

Fail on the plug-in GFCI tester (i.e. it trips!) indicates they have bootlegged ground at the GFCI receptacle- attached the neutral wire to both neutral and ground. It will seem to work at the GFCI, but is still dangerous.

Bootlegging ground at a downstream GFCI receptacle is a mistake, because one of several electrical faults could put 120V on the the grounds, e.g. the cover plate screws or a machine chassis. However this is difficult to detect, since a properly wired downstream receptacle will behave exactly the same way. This means for ungrounded downstream receptacles, plug-in tester testing is completely meaningless.

Once you have settled the question of bootlegged grounds, here's how you test an ungrounded GFCI. Plug your GFCI tester into your handy dandy 2-3 prong "cheater" - the kind with a short green wire as a pigtail. Extend that green wire all the way to a reliable ground source, e.g. the panel in the basement. Now, the GFCI tester should work normally, since you have rigged a proper ground to it.

GFCI protection is pretty effective, and I would be confident in an ungrounded circuit if it has GFCI protection. However if you are unable to get the external device to trip, you'll need to pop the cover off and see if the ground is present, missing or bootlegged.

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In turn:

  1. The answer is yes -- if the TEST button trips the GFCI and it stops providing power, then the GFCI is good.
  2. This is a classic behavior of a GFCI that has no earth ground connection, which is fine (it will still provide full protection)
  3. "GFCI testers" put a small load from load hot to ground, while the TEST button applies a small load between load hot and line neutral (or vice versa). As a result, the TEST button works no matter if the GFCI device has a ground connection or not.

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