Two rooms in our house have older electrical wiring: two-wire 12 gauge insulated wire (no ground wire) that looks like an older version of romex (no metallic sheathing). These wires terminate outside the electrical panel at a 15 AMP GFI. The GFI is connected to the panel.
I recently replaced three older outlets that had been painted over too many times with new ones. As expected, the outlets in the older part of the house all show an "open ground" on my plug tester.
However! After I replaced the outlets the very last outlet on the circuit now displays "correct" on the plug tester! This surprised me: no other outlets in those room display this reading and there is no metallic sheathing terminating at the metal boxes and I know the two-wire terminates at the GFI.
Am I experiencing some kind of "phantom" voltage in the box enough to fool the plug tester?
I took it apart again and used my multimeter and put one lead on the hot wire and one lead on the metal box and found a voltage reading of 120v. (For comparison, I tested another box around the circuit and got a voltage reading closer to 30 volts.)
I unhooked the metal clamp and freed the incoming wire (just to see if any was frayed or maybe touching the box) but even with the wire suspended in mid-air I am still getting voltage reading from the metal box.
I am a little perplexed and don't have much experience with jumping/phantom voltage (if this is the case).
I am inclined to remove the metal box and put in an old work PVC box but I wonder is there something else I need to consider?
I have removed another box in a different part of the room and didn't find any secret grounding or bonding behind it and and suspect this is the same.
Appreciate your insight.