My house was built in the 1940s and only part of the electrical has been upgraded. I am trying to replace an old outlet on my screened in porch with a weather resistant GFCI outlet but cannot get it to work. There are two sets of wires coming into the box, each has a black and white wire, no ground wire. Both black wires were connected to the black terminals on the old outlet and both white wires on the opposite side and everything worked fine. Using my multimeter, I found which black wire was the "hot" wire (line wire) and also determined the metal electrical box could act as a ground.
I connected a ground wire to the box and the other end to the ground terminal on the GFCI outlet. I connected my black hot wire to the hot wire terminal on the line side of my GFCI and then the white wire from the "hot" bundle to the neutral terminal of the GFCI on the line side. I then connected the black and white wires from the other bundle to the hot and neutral terminals on the load side of the GFCI (sorry I didn't take any pictures). Unfortunately the outlet doesn't work and neither do the electrical lights downstream of the outlet. I cannot reset the GFCI and cannot get anything to work in the outlets.
I did check the wires using my multimeter and with my red probe touching the hot wire, I will get a reading of 120 volts when touching the neutral terminals on my GFCI and the electrical box. But if I have my red probe touching the black wire on the load side of the GFCI, I won't get any voltage readings. Also, when I take the GFCI outlet out and replace it with the old outlet, it works again.
Does anyone know why I am having this issue? Am I wiring it incorrectly? Is the wiring of my house not correct? Any help would be appreciated.
Thanks,
Brian
Best Answer
OK first of all you cannot determine whether the box is properly grounded just using a multimeter. The fact that it reads "0V" does not mean it is properly grounded. The only way to determine that would be to confirm that there is a proper ground wire all the way back to the panel, or to confirm that grounded armored cable is used. In your case I would just forget about the ground and disconnect it, you don't need a ground for a GFCI.
Second, try to get the GFCI outlet working without the downstream outlets hooked up to the LOAD side. If you can get the GFCI working by itself but it trips when you hook up the downstream wires, that probably means there is something downstream creating a ground fault and the GFCI is tripping (as it's supposed to). A common cause might be a neutral wire touching a metallic box or a "bootleg ground" where neutral and ground are connected.
If the GFCI doesn't work even on its own, it's probably defective.