How should I wire my GFCI?

There are 5 wires from the box, two blacks, two whites and a copper wire. I used a multi-meter to test the blacks they both have voltage of 117v (-ish). One white has 30v (-ish) and the other white has none.

If I wire all of them to GFCI, two for Line and two for Load, its led turns green but it cannot be reset and there is no power from its socket.

If I only wire 1 set of black and white it works.

What should I do? Should I connect them to the same line port?

To fully power of this I have to switch the Disp and DW breaker off. (They are link together as the picture)

Edit: (add some images). Note both black wire have voltage before I group them like this so don't blame me. Both black wire have voltage before I group them like this Both black wire have voltage before I group them like this enter image description here Breaker

  • 1
    The 30V is probably phantom voltage (i.e., not "real", will go away under any significant load). But 117V on two blacks is concerning, and could mean a few different things. Can you upload pictures of the wires/junction box? Mar 16, 2021 at 18:40
  • Why do you want to connect to LOAD? Are there additional outlets you want to protect from this GFCI? Do you plan to install the "GFCI Protected" stickers... is this all going over your head? Mar 16, 2021 at 18:58
  • @Harper-ReinstateMonica. I don't know but the old GFCI have them and it work just fine. I'm new to the whole system. I don't know where the wire go to may be there will be another socket
    – James
    Mar 16, 2021 at 21:25
  • 3
    Interesting. What motivated you to replace the GFCI in the first place? Did it seem broken? (happens all the time). Mar 16, 2021 at 23:06
  • 1
    Can you please post photos of the inside of the box in question? Mar 16, 2021 at 23:38

1 Answer 1


The black with the 117 ish and the white from that same cable go to the line side then the black with 30 and that white go to the load. Make sure to get the correct black and white wires coming from the same cable on each side this configuration will provide GFCI protection to everything down from the GFCI connect the bare copper to the green ground screw. The 30 ish in almost every case phantom voltage it has no real potential and is induced voltage because the line wires are running with the load , nothing to worry about. This is how transformers work but they have lots of wire in close contact so you get the current there but not here.

Edited ; I misread the voltages thanks to doxylover, the white wire that appeared grounded and the black in cable that it is with is probably the line side The black and white on the load showing a voltage is still phantom, if we want to verify this the safest way is to tie the 2 whites together then with the blacks not connected plug in a load down stream the whites instantly go to ground when connected and since the 1 phantom black is now connected to a load the voltage will dive. If a hair dryer or other large resistive device is used the voltage on the load black will be close to zero but maybe a few volts. The line side black won’t change still 117 and the white that that black comes in with is the proper neutral for the line side.

  • 2
    As I read it, the OP said he saw 117 volts on both blacks. It sounds like doggy wiring to me.
    – DoxyLover
    Mar 16, 2021 at 19:38
  • 1
    I may have mis read that but that would normally be the load side neutral as it is not connected to ground and the line side is.
    – Ed Beal
    Mar 16, 2021 at 20:24

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