Re: Ground fault / residential
However, a GFCI tester will not work because these do need the equipment ground to operate.
The way that the test button in a GFCI works is by connecting a small resistor around the outside of the current transformer that senses ground faults, what is known a primary injection. For instance, the internal tester runs current from the hot lead on the load side of the CT to the neutral on the line side of the CT.
However, a plug-in tester does not have access to the line side of the CT so it must use an equipment ground.