How well will a GFCI circuit be able to detect current flows, if both the "hot" input and the (supposedly) "neutral" input to a GFCI outlet are energized?
The reason I am interested in this is that I am renting an old (1915) townhome and have discovered that an (ungrounded) wall outlet and a ceiling fixture are both controlled by a wall switch that opens the netural wire instead of the hot wire. The result is that when switch is off, the direct neutral line is open, but the netrual input of the GFCI is connected to hot. When I reported this to the landlord, their electrical contractor put in a GFCI, but they do not want to correct the open neutral. (I think it may be a knob and tube circuit with only the neutral line going through the wall switch, so fixing it may require pulling apart the wall and/or rerunning the entire circuit.)
For what it is worth, when the switch is off (and both inputs are energized), the GFCI test button will trigger a disconnect, but the reset button is not functional. But I'm not sure if the test button guarantees that the GFCI is providing effective protection in this scenario, hence my question: will a GFCI circuit work when both inputs are energized and it has no real neutral and no ground?
Best Answer
A GFCI is only measuring currents and does not care about the voltages on either of the two wires going through it.
As long as the net current is always zero, it really doesn't matter how it is switched on and off.
The real problem with a "switched neutral" is that the contacts inside the fixture are live with respect to ground even when the switch is off. If you should accidentally touch the contacts while grounded, the GFCI will protect you by tripping. But if the fixture were wired correctly, that particular risk wouldn't exist at all.