Jadnashua
Retired Defense Industry Engineer xxx
A GFCI receptacle does not use the ground at all. It compares the power going out the hot side to that coming back on the neutral, and if they differ by more than about 5ma, it trips. Those 5 milliamps must have found another path to ground, possibly going through you, and then it trips to remove the power.
Now, in the scheme of things, in order of increasing overall safety it would be:
- two wire receptacle
- two-wire polarized receptacle
- grounded 3-wire receptacle
- two wire plug with GFCI protection (and maybe an AFCI)
- 3-wire with GFCI
- 3-wire with GFCI and AFCI
The house I grew up in was originally wired with BX, that MIGHT have provided a ground when it was new, but certainly did not after a bit of age and rust. Metal boxes today should be grounded, but they often weren't, at least in a reliable manner, ages ago. That meant that using one of those adapters with the pigtail intended to go on the cover mounting screw were often useless to anything that really wanted a ground.
I replaced the first receptacle in each circuit that needed it with a GFCI. That was cheaper than replacing the breakers, which might have made the discovery of the first in each chain as long as you don't have to pay the labor of someone doing it for you.
Some devices expect a real ground to perform their full functionality, but for safety, a fully functional GFCI means you should never get electrocuted. Without a ground, you might not trip the breaker or blow the fuse, as over-current is not something the GFCI monitors.
Now, in the scheme of things, in order of increasing overall safety it would be:
- two wire receptacle
- two-wire polarized receptacle
- grounded 3-wire receptacle
- two wire plug with GFCI protection (and maybe an AFCI)
- 3-wire with GFCI
- 3-wire with GFCI and AFCI
The house I grew up in was originally wired with BX, that MIGHT have provided a ground when it was new, but certainly did not after a bit of age and rust. Metal boxes today should be grounded, but they often weren't, at least in a reliable manner, ages ago. That meant that using one of those adapters with the pigtail intended to go on the cover mounting screw were often useless to anything that really wanted a ground.
I replaced the first receptacle in each circuit that needed it with a GFCI. That was cheaper than replacing the breakers, which might have made the discovery of the first in each chain as long as you don't have to pay the labor of someone doing it for you.
Some devices expect a real ground to perform their full functionality, but for safety, a fully functional GFCI means you should never get electrocuted. Without a ground, you might not trip the breaker or blow the fuse, as over-current is not something the GFCI monitors.