Last year I installed an old GFCI outlet in a switch box. As verified with a multimeter, the white wire is neutral, and the black wire is hot. Note that this picture was taken after I took off the wire nut connecting the three white wires. At the time I installed it, everything worked fine.

Yesterday, I plugged an AC outlet tester, and it reported a swapped hot and ground. When I tested the outlet with a multimeter, I found that both prongs (as measured at the screw termminals) were were 120v to ground, and there was zero voltage between them. I replaced the outlet with a new one, and everything seems fine now.


  1. How could a GFCI fail this way?
  2. Is it likely that the GFCI should be thrown away?
  3. Why would this not trip the circuit breaker?



The GFCI is shot, the internal circuitry failed, the voltage measured on neutral may be a leakage from the damaged circuit very little current available but that’s probably why you are reading voltage. Why it did not trip the circuit breaker probably same issue the neutral opened. There are several different types of circuits used by the different companies so it is hard to tell the true cause. I do see failed GFCI’s regularly where garbage disposals are connected and less often but still several times a year where a vacuum cleaner is used on the circuit. These motors are very hard on the electronics in my experience.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.