Why might hot and ground light a circuit tester; neutral and ground also light; but hot and neutral do not light a circuit tester?


I opened an old box to branch a new receptacle.

I used the circuit tester against the hot and neutral wires. It did not light.

I tested the circuit tester against hot and ground. It lit.

Neutral and ground also lit the tester.

I have never seen this before. What's going on? Is it possible the previous homeowner accidentally used ground for hot or neutral?

  • Do the previous receptacles read the same way? Can you get a voltmeter and get us H-N, H-G, N-G voltage readings at both the old and new receptacles? Apr 13, 2020 at 23:57
  • The box in question is a junction box in the attic. Without further discovery unsure which receptacles come from it. Will take a closer look tomorrow. In the meantime, the closest receptacle lights with H-G and H-N. N-G does not light. Apr 14, 2020 at 0:29
  • Can you plug in a two-prong (double insulated) load into the weird receptacle and have it work? Apr 14, 2020 at 0:50
  • Also, was there a receptacle, a switch, or both in the box you branched from? Apr 14, 2020 at 4:37
  • All, the box in question is a junction box (so can't plug anything in). I verified that the receptacles nearby all work as expected. Apr 15, 2020 at 13:13

1 Answer 1


Because Black = hot and White = neutral is not actually a hard and fast rule in household wiring. You are probably looking at a switch loop - no longer approved for new installs, but approved recently enough to be quite common. The white wire that's hot SHOULD be marked in some way to indicate that, but often is not, or the marking was impermanent. Red tape or paint or black tape on white wire are common methods of marking a white as not being Neutral.

  • This is the most plausible explanation so far. I turned on / off all nearby switches with no effect on the H-N, H-G and N-G tests with the circuit tester. However, this was not a comprehensive test of ALL switches in the house. Still somewhat of a mystery. In the interest of safety, I branched off a nearby receptacle instead for the new outlet. This is resolved, but still curious what the function of that box is. Apr 15, 2020 at 13:24

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