Diagnose 125v 20a receptacle voltage

Question

I am replacing a 20A 250V receptacle with a NEMA 5-20 and am seeing voltages I can't explain.

• Hot-ground: 122v
• Neutral-ground: 20v
• Hot-neutral: 95v

What could be the problem here?

Details

1. Turned off main
2. Removed 2 pole circuit breaker
3. Capped red wire
4. Installed 1 pole breaker and connected black wire
5. Turned on main
6. Remove old receptacle, discover there are only 3 wires - white, black, ground (this receptacle is labeled 20A 250V)
7. Installed NEMA 5-20 receptacle - black to brass, white to silver, ground to green as per instructions.
8. Read above voltages

Where did my red wire go?

I am certain I replaced the correct breaker. No voltage when I turn the breaker off.

The wire appears to be 12 gauge.

My outlet tester is inconclusive because all three lights appear to be lit.

Answer 1

So in the breaker box, you have black, red and ground but in the outlet box you have black, white and ground.

Odds are that you have a junction box somewhere where the red wire is connected to the white wire. Since you capped the red wire in the breaker box, the white wire is not connected, just floating.

I’m also assuming you checked the voltages with a digital voltmeter. In this case, you’re seeing a phantom voltage, induced from other wires. The voltmeter provides very little load.

To test this, plug an outlet tester into the outlet, it should show “open neutral”. You can also measure the voltage with the tester plugged in. You should now see 120 volts (or nearly that) on the white, conducted through the tester.

Assuming all of that proves true, you need to land the red wire onto the neutral bus in the breaker box. I’d also suggest marking the end of the red wire as white, either with paint or tape.

Answer 2

More than likely you have a junction box, receptacle or switch between there and the panel that drops the neutral and passes the "red" hot over the white wire.