On an inspection yesterday, the GFCI in the kitchen would not trip when I used my 3 light tester. When I tried the test button, it did trip and did not have power. When I plugged my tester into another receptacle, the GFCI did trip.
Why would it trip at another receptacle but not when I plug the tester directly into it? I have encountered similar before but in those cases, the GFCI still had power when it was tripped.
This comes up frequently on this forum many strings on GFCIs .see
I have experienced that with ungrounded GFCIs before but this one was grounded.
I have also encountered ones where the line was connected to the load terminals. In those cases, the GFCI receptacle still had power when it was tripped. In this case, the GFCI. will trip with the test button or a down stream receptacle but not with the tester plugged directly into it.
When it trips,it does not have power.
It is obviously a safety concern because if it will not trip from my tester, it will not trip if it needs to. I am just trying to figure out what would cause this.
I don’t think the manufacturers agree with that logic. The device’s ability to trip isn’t tied to your external tester’s “test button” functionality.
Mis-wired circuits account for most faulty GFCI issues, including functional receptacles that don’t “test” upon demand.
Dom.
The only recognized method to test a gfi is the built-in test button, not a 3 light tester.
With very few exceptions, if the GFCI does not trip with my tester, it also will not trip with the test button on the device. In almost all of the cases where it did trip with the test button, I found that the GFCI was not grounded or it still had power after tripping it with the test button indicating that it was miswired.
In this case it tripped at a remote receptacle and with the test button but not with the tester connected to it.
I don’t know about you, but I would not want to trust my life with it based on the way it responded to my testing. If I would not trust my life with it, I am not going to fail to call it out as a problem and trust that it will protect my customer either.
Did it trip with your back-up tester? You do carry a back-up tester specifically for this scenario, right?
.
Sorry I disagree with you .
Homes with Knob and tube can be protected by installing a GFCI in the first Receptacle in the circuit .
Using the receptacle test button will trip the circuit .
Using your simple three button tester will not trip the circuit .
see below on how to test the receptacle
Which is why as long as it trips with the device test button I care little if my 3 light tester trips it. 
I was taught early on the built in test button always trumps what the 3 light tester says because this issue can and will come up from time to time.
this has also happened to me, sometimes I write it up and others I remove the tester re plug it in and try it again and then it trips…
With that said , what are you thoughts on using a circuit analyzer after testing the button at the receptacle like the one by amprobe?
Sorry Ken, not an inspector and do not have a circuit analyzer.
You can test a GFCI device with an old solenoid style or low resistance tester simply by testing from the hot leg to any grounded object, even a nearby grounded water pipe will trip the protection.