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fishmanflats 12-23-2009 06:34 PM

open circuit unknown location / voltage leakage
This will be a little long. I called an electrician who will be out on Saturday, but I wanted to get some advice going forward.

My wife started the vacuum cleaner today and killed a circuit. No breakers were tripped so I reset all the breakers, still the circuit was dead. I replaced the circuit breakers (new from depot) and still nothing. There is residual voltage in the circuit at the panel and at the first receptacle. (I have a 1952 house with a newer panel, all copper.)

The wiring going to the receptacle has three wires; red, black and white and metal cable outside. At the panel i noticed that the red and black on this line are both energized to separate breakers. The red and white are connected to the receptacle and the black is wire capped to another black wire of another set of wires (red, black and white). The red and white are connected to the same receptacle as the lead from the panel. When I shut the circuit off for the red at the panel, I have about 6 volts at the receptacle between the second set of red and white and the the black wire at the panel.

I am having a hard time understanding the creative wiring here and trying to find the 1) source of the residual/voltage leakage and 2) why the circuit is open somewhere (no power on the rest of the circuit). I am assuming a wire got fried somewhere and the odd wiring did not trip the breaker.

For the time-being, I shut off the breakers off. I have lived in this house about 10 years and have not had any other issues.

Has anyone experienced something like this?

Thanks and Merry Christmas.


hayewe farm 12-23-2009 07:29 PM

You are probably using a digital meter and the residual voltage means nothing. It sounds like you have 2 circuits with a shared common. The cable leaving the outlet box probably goes to anther outlet box and somewhere along the line the black and a whit goes to a different set of loads.

220/221 12-23-2009 07:58 PM

1) Forget about the 6 volts.

2) Your circuit is not uncomon. It's actually two circuits using the same neutral (white) The red wire is one hot and the black is another hot on a different breaker and a different leg. Your voltage will be 240 volts between black and red if it is wired correctly.

The way you described it, it sounds like the recep with the red wire is working and the problem is downstream on the black circuit.

The wiring in your house goes from one recep/switch/light to another in a somewhat logical manner. One common failure point is at a recep. The recep is often used to connect the incoming and outgoing wires by stabbing them in the back of the recep instead of landing them under the screws.

You can pull out a few receps and see if you find anything amiss.

Do not do this hot and whatever you do, don't take apart any white wires while the circuits are hot.

Yoyizit 12-23-2009 08:29 PM


Originally Posted by fishmanflats (Post 371333)
My wife started the vacuum cleaner today and killed a circuit.

The heavy load caused a bad connection to fail to an open circuit. Wire insulation near the bad connection might be charred.

Your house is safer now because an open circuited "connection" cannot heat up from current flow and cause a fire.

As a coarse test, I recommend plugging a hair dryer into each outlet to look for other trouble spots. If it doesn't run at full speed there is a connection integrity problem.
A voltmeter plugged into the same outlet will let you can run more sophisticated outlet tests. With the dryer on, a good outlet will drop the voltage no more than about 3vac, depending on the wire size and the distance to the panel.

fishmanflats 12-23-2009 09:04 PM

I will look at all the receptacles tomorrow that seem to be on the same circuit.

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