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Given old two-prong (ungrounded) wiring where a GFCI is installed nearest the panel and other two-prong outlets are attached to the load side of that GFCI, how does one confirm that all the outlets are properly protected?

As far as I understand things, a GFCI tester must leak some current to earth to confirm that it triggers a fault. With the earth pin unconnected that test can't be done with a conventional three-prong tester.

Is there a more sophisticated test? Or is there simply no such thing as downstream protection in ungrounded circuits? Must every outlet have its own GFCI?

  • Don't waste your money installing GFCIs everywhere. One will suffice. Your notion is correct that a tester can't test a GFCI without a third path to leak current into. – Harper Nov 26 '17 at 20:42
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Testing the initial GFCI receptacle should be sufficient. No need to test the load side receptacles since they are protected by the GFCI. If the GFCI works, and the 2 prong receptacles are connected to the load side of the GFCI, then they are protected.

If however, you wish to pursue it, you would need a separate conductor run to a good ground. Insert the tester into a 3 prong to 2 prong adapter and attach the ground to the ground prong tab (or wire) of the adapter. Then plug in to each of the old 2 prong receptacles to test.

Good luck!

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    I don't have a lot of faith in what should work and I'm not comfortable putting the "GFCI protected" tag on an outlet I have not tested directly, no matter how much common sense tells me it must be protected. Anything could be going on within these 60-year-old walls. Looks like I'll have to build a rig for this. – sh1 Nov 26 '17 at 23:16

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