Question for Site Sparky's

[WIP]

I have a question for the electrical people. When replacing an old duplex receptacle with no grounding slot in existing construction that does not have a grounding conductor, I believe the NEC allows for the use of a GFCI properly labeled "no ground." I realize this is not ideal but allowed rather than having to replace the entire circuit.

First question might make my second question a moot point. Am I correct with the above statement?

Second question is why does NEC allow this?

My understanding of how a GFCI works in simple terms is that it monitors the current flow on the ungrounded and grounded conductors for an imbalance in excess of 4 or 5 mA and if detected immediately opens the circuit.

Couldn't this still potentially expose a person to a ground-fault situation? Suppose an appliance like a microwave is plugged into a GFCI that is not wired with a grounding conductor and a ground-fault becomes present within the microwave resulting in live power on the exterior of the oven. Since there is no grounding conductor, the current flow would have only one path and that is through the grounded conductor unless some other form of conductive material touches the exterior of the oven, such as a human.

The only explanation I can come up with is that the GFCI is expected to trip and open the circuit within about .03 seconds so this should be fast enough to protect the person.

 

[JohnDB]

A GFCI will not work appropriately without a ground...don't waste your money on a GFCI plug when a normal one will do.

Bootlegging (making neutral a ground or vice versa) is how people get hurt. So don't do it.

If you need a working GFCI then run a single green wire from the outlet box inside a wall through to either floor or attic to a nearby copper cold water pipe and bond it to the water line. Chances are that the water line is bonded to a house ground to begin with.

Then you will have a great ground and your GFCI will work appropriately.