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.

A GFCI does not have to have a path to ground to work. It detects current flowing outside of the normal hot-neutral circuit as already described and assumes the leakage is through something else bad but it doesn't actually have to determine where it's going.

A warning on replacing GFCI's! A few years ago they changed the connection points so the old "Line In" and the "Out" were reversed on new GFCI's. If you don't look closely at what you're doing and hook the new one up exactly the same as the old parts, you can put the new one (or a whole kitchen full..) in backwards and it will be dead (but not damaged). Don't ask me how I learned this lesson..