Intermittent low voltage on one leg

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IT'S FIXED! I called Duke Energy early this morning and restated my case for getting a monitor on the meter. Later in the morning I got a notification email that my Honeywell thermostat was not communicating. It has something called Total Connect that allows you to control the thermostat remotely via a web browser. I was at work so I assumed Duke had pulled the meter at my house to put on a monitor. However, I got a second notification email an hour later so I decided to go home to check things out. The problem was back and Duke hadn't been there yet. I was afraid it was going to start working before they got there so I called to see if they could expedite the service call. I wanted their tech to see the problem for himself.

In the meantime, I disconnected the air conditioner so it wouldn't come on and "fix" the problem. I think that by drawing 240v the A/C, range and/or water heater may be what was "fixing" the problem in the past. The Duke tech arrived about 30 minutes later. It was the same tech who left the door tag saying everything was fine on their side. Before he pulled the meter I took him to the circuit breaker panel, turned off the main breaker and showed him that the voltage was low on the suspect supply line. He started saying it could be this or that but he checked it at the meter and found there really was a problem with their supply line. He disconnected our house at the transformer and used a Vision FLX locator to find the bad section. The wire was corroded and falling apart. After he cut out the bad section and spliced in a new section everything was good.

FWIW, here's my theory on what created the problem to begin with... our section of the development is about 2 years old but the street lights weren't installed until about a year ago. The bad section of wire was about 2-1/2 feet from the concrete footing for the street light. I suspect they nicked or partially cut the wire when they were digging (perhaps even drilling with an auger?) the hole for the footing. They probably realized they hit wire or something and simply moved over a couple of feet.

Thanks to all for your assistance and input!
 

Reach4

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Does everyone agree that if the low voltage condition exists with the main breaker off then the issue is not the circuit breaker panel or house wiring?
Yes. But not the other way around... if the voltage looked OK at the input terminals with the breaker off, there could be a high resistance in one of the lines, and that would still give good looking voltages.

I am going to call the good leg L1. If I understand correctly, you are probing the input terminals and see 120 VAC from L1 to neutral but much less than 12o from L2 to neutral. Not much to go wrong with your test procedure there. It sounds to me as everything you are doing is the right thing.

When things work, you should get about 240 L1 to L2, and much less during the problem. Turning on the oven would make some L2 to neutral voltage, but the L1 to L2 voltage would go down a lot in that condition.

Unlikely to be the case, but you could measure the voltage between the L2 wire and the L2 terminal that clamps that wire. (talking about probing two spots maybe 1/4 inch apart, just to be clear) If that does not read zero, you found the problem. But with your electrician tightening that terminal more, that is very unlikely to be the problem area.
 
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BadWire.JPG
 

jadnashua

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Most people don't think of aluminum degrading like that, but under the right conditions, it can happen, and it can happen fairly quickly.

Look up thermite reaction and see how much aluminum really likes to combine with oxygen! Once you get the reaction started, powdered aluminum will pull the oxygen out of iron oxide (rust), leaving molten iron. Gives you an idea how much aluminum doesn't like being elemental.
 

WorthFlorida

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Most people don't think of aluminum degrading like that, but under the right conditions, it can happen, and it can happen fairly quickly.

All you need is a small hole or extremely small cut in the insulation on buried aluminum wire and the process will start. Back in 1982 my neighbor asked me to help him restore his telephone service (I'm a retire telephony engineer) after someone install a patio deck. I was digging with a small hand garden shovel looking for the telephone wire at one 4x4 post near the electric meter. I felt an AC tinkle when I touched the underground power cable (I didn't see it but I felt it). The very next day the wire burned open and lost power to the house. Three days all it took as Jadnashua explained.
 
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