GCFI "test" button will not cause a trip

Question

Preface to OP: I am a dope. The reason the GFCI does not trip when I push the "test" button is because the GFCI has failed. That's the whole point of the "test" button. End of story. Read on only if you want more details about how the things work.

I've noticed a GFCI outlet in which the "test" button depresses but does not cause a trip. Pressing the "reset" button temporarily disables the outlet, until it is released (which may be normal behavior).

I don't have a GFCI tester, so I tested it by shorting a 10K resistor between hot & ground. That's 12ma or so, which appears to be well over a typical trip threshold; and I've tried it on newer ones (elsewhere in the house) and it trips them just fine.

Furthermore, I have TWO GFCI outlets that are exhibiting this exact same behavior. However, they are the same brand and were installed when the house was built 32 years ago. Is this a known failure mode ? Seems like the problems most everyone reports are needless trips.

P.S. They were not wired incorrectly (e.g. "hot" to "load" terminals).

Answer 1

This can happen, just replace the GFCI outlets in question

The TEST button on a GFCI creates an actual ground fault (about 6-8mA, maybe up to 10mA, from load-hot to line-neutral or vice versa), so if a GFCI fails to trip when the TEST button is pressed, then it's dead and needs to be replaced. This can happen due to improper wiring (backfeeding a GFCI's LOAD terminals will burn out the trip solenoid), or more commonly due to damage to the GFCI's (largely analog!!) electronics package caused by mains surges and spikes. (More modern GFCI designs may have a varistor connected across line-hot and line-neutral to help protect the electronics from surges, but this is by no means guaranteed.)

Answer 2

This is exactly WHY there is a TEST button.

The TEST button is so that you can "test" the device. There are known failure modes, and because this is a life-safety device, testing is important. Many newer GFCI devices actually have automatic testing since most people don't bother with monthly (or yearly) tests of their GFCI devices. The automatic testing effectively (if it all works...) turns the device from a fail deadly (i.e., always "on" so failure is failure to turn off = deadly if there is a ground fault) into a fail safe mode (i.e., the automatic testing simulates a ground fault and if that fails then it will turn off, so that there is very little possibility of "on and not able to turn off when there is an actual ground fault").

How much electronic equipment do you have that lasts 32 years? Are you using the same TV, computer, smoke detector or any other sophisticated electronic device that you used 32 years ago? GFCIs are relatively simple, but they do wear out, just like most other electronic items. Unlike most, they have a test button. Actually, your smoke detectors also have test buttons, but now they are designed to be replaced after 10 years whether you like it or not - because too often the detector mechanism or other parts fail and too many people don't bother to test.

Nuisance trips are sometimes a too-sensitive or otherwise failing GFCI. More often they are appliances or other devices plugged into the GFCI circuit that actually have a ground fault.