I was going to upgrade a standard duplex outlet to one with USB capabilities, when I found the wiring to be... strange. The outlet's power can be killed by shutting off Breaker A. However, a proximity tester still showed voltage that only went away when Breaker B was also killed. I pulled things apart and did some voltage testing with a digital voltmeter with each breaker on or off or in combo.

(Incoming romex = 2-wire+G wire entering gang box on left side. Outgoing romex = 2-wire+G entering gang box from right side.)

Breaker A and B off: No voltages of any significance on any combination of wires.

Breaker A off, Breaker B on:
Incoming romex - no voltages of any significance. Outgoing romex - Neutral to ground shows 115V. Hot to ground shows 115V. Hot to neutral shows no significant voltage.


Breaker A on, Breaker B off:
Incoming romex - hot to ground shows 120V, neutral to ground show no significant voltage, hot to neutral shows 120V. Outgoing romex - no significant voltage on anything.

Also, Hot on incoming romex to Hot on outgoing romex shows 120V. Same with hot on incoming to neutral to outgoing...


Both Breaker A on + Breaker B on:
Incoming romex - Hot to ground shows 120V, neutral to ground shows no significant voltage, hot to neutral shows 240V! Outgoing romex - 115V hot to ground, 115v neutral to ground, no significant voltage hot to neutral.

I suspect crossed circuits somewhere... but I don't really know what the heck is going on. The outlet was working just fine how it was wired before, too...

Oh, when it's all wired together to the outlet, the outlet tests with 120v on hot to ground, 120v on hot to neutral, and no significant voltage on neutral to ground. Also, killing breaker A will kill the power to the outlets, even if Breaker B is active.

 

Welcome to the forums!

just as of note, a non-contact tester is just good for a quick test. They are not good for troubleshooting.

I think you have something crossed, as you suspected, and it involves a multi wire circuit.
You should have 120 volts from hot to neutral. Are you testing with all wires disconnected from each other? Were the wires all connected tot he outlet or were they pigtailed? You could be reading through something that is pluged into the circuit elsewhere.

 

Thanks Tolyn!

Yup, I just use proximity testers as a quick way to see if there might be a live wire in my work area. I then follow up with a voltmeter.

When doing the testing, I had all wires disconnected from one another. The wires were pigtailed to the outlet via wirenuts (three wires in each nut) when the outlet was assembled.

And again, when everything was assembled, all the voltages were as one would expect, and killing Breaker A would kill the power to the outlet, regardless of whether or not Breaker B was active or not.

I wouldn't be surprised if there was a miswired multiwire circuit somewhere. I've also found switches in this house (built in 1979) with switched neutrals instead of hots. I don't know why they were done that way.

 

Connect the white wires together again and recheck your voltages. Change in thinking: I suspect you opened up the neutral of a multiwire circuit and the other circuit had a load on it. This would give you a reading of 240 volts hot to neutral.

BTW - What is your location and how old is the house?

 

I agree with you Tolyn but technically that isn't the common neutral point. He should be working on only one half of the circuit as I haven't read anything in the thread about a red wire.

 

Tolyn,

I've reassembled the outlet as it was before I messed with anything, as I don't have much more time today to devote to the troubleshooting. =( But when everything is all wired together, the voltages all seem proper.

There is no red wire to be seen anywhere within this gang box. Also, would a 3-way switch on the circuit ever cause both hot and neutral to show 115v to ground?

I'm located in SW Michigan and the house is 36 years old (built in 1979).

I think there is one pair of 3-way switches energized through Breaker B. I wouldn't be surprised if there is something not quite right with them as I've found a couple 2-way switches in this house switched on neutral.

 

The red wire is someplace else. He is reading from the A phase, through something like a light bulb on the B phase. This could give 240 volts from hot to neutral.

You mean single pole switches Are you sure they were not just a switch loop? Not too many switched neutrals on a 1979 house unless it was done wrong.

 

Sorry yes... I always get confused on switch terminology. Searching online they always say 3-way for two switches that control one light. But in this case, these were single pole switches switched to neutral, in no loop. I found out the hard way when I cut through one cable leading to the light when the switch was off and sparks flew everywhere. Now I don't trust switches and make sure the breaker is off.

 

That doesn't necessarily mean the neutral was switched. It sounds more like a proper switch loop and even with the switch off, you cut through the hot wire and ground wire.