GFI electrical question

JRscooby wrote:

BB_TX wrote:

theoldwizard1 wrote:

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

This is correct. However, there must be some ground path back to the power source for the GFCI to be able to have a discrepancy between the current in the hot pin vs the current in the neutral pin. The GFCI works on the principle that that there is some current "leaking" out of the circuit. For there to be any current flowing outside the circuit in question, there must be some path for that current to flow back to the source. Electricity requires a closed path to flow. If that path does not exist, then current can not "leak" out of the circuit. In old ungrounded homes, that ground could be plumbing at the various sources of water.

That "leak" the GFI is detecting is what is running up your arm on it's way to ground. For decades, normal house wiring was only 2 conductors to outlet or lamp. There was no path to the water pipe for most uses.

Electric current requires a closed circuit, meaning a path back to the power source. Basic fundamental of electricity. In the case of utility power it means a path from hot back to earth ground or to neutral. It can’t just leak out to anywhere it wants. “Running up your arm” will only happen if you are grounded in some manner to the source or touching neutral. Standing on the ground would do it. Touching a metal plumbing pipe or fixture would do it. You can hold a live 120 vac wire if you are completely isolated from any other path to the power source.
https://www.dummies.com/article/technology/electronics/general-electronics/closed-open-and-short-circuits-141399