I have a friend who called me over to check his garage voltage out. He had some 120 volt outlets not working. He has a 120/240 feeder coming from his house feeding underground to a garage about 75ft. away. I check the voltage and find out that there's one phase not getting the right voltage. I was getting 123 volts to ground on one phase, and around 74 volts on the other phase. At first I thought one of the conductors were broken or burned under ground, then I traced it down to a HID fixture mounted on the outside of his garage. When I turned this breaker off, the voltage came back to 245 volts between phases. I then hooked up everything the way it was before ( I had to change the piece of rusted conduit that was coming up into the panel. After I hooked it all back up, I checked the voltage again. It corrected the voltage almost, but I'm still getting 123 volts on one phase and only about 111 volts on the other phase. Still seems to be something not exactly right.First question is how would a bad ballast in the light make the power to fluctate on the main lugs like this? 2nd question: Do you think there still might be a "bad wire" under ground causing the difference in voltage on the two phases? Thanks for the input.. Steve

Sounds to me like an underground problem. When there is no heavy load, likely you read "normal" voltage. When load is applied, then the probs manifest itself.

Yes, a bad wire. A bad neutral wire.

Since the neutral path back to the main panel is broken, you aren't drawing current from a hot wire and neutral. You are drawing current from the hot wire and all of the appliances, lights, stereos, etc on the other hot wire.

When the load is balanced perfectly between the two legs, the voltage will be balanced. Any imbalance in load will cause an imbalance in voltage.

I would check the neutral out, it's connection, and also the connections of the grounding electrode. I've seen a corroded attachment to a grounding rod cause some odd things, like getting 75 volts from the water running out of a faucet to a stainless steel sink or a guy's wife getting a shock by the water in her washer.

111 volts on one leg is indicative of the failure being on that particular hot leg, not the neutral. It should be easy to determine by removing all loads and measuring between each leg to the neutral (NOT the ground).

Ed, what if it measures 111 on one leg, and 129 on the other?

(The neutral would be the suspect)

I agree with your method of removing the loads, it should read 120 on A, and 120 on B to the neutral conductor.

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If it's a separate structure, then it needs to comply with 250.32(A) in regard to having the required grounding electrode installed, and its connection.

Thanks for the replies. I haven't got a chance yet to go back and check the voltage again. It only has a 3 wire feeder to the panel in the garage. There was some digging in the near proximity of it a few months ago( 3 feet or so), but the owner hasn't said anything about any problems til now. I guess it's possible a wire got nicked somewhere, and is just now deteriorating to the point of causing a problem. We will just have to dig in the general area and see if that's the problem. I originally told him, it looked like a wire was broken underground, so we may still have that problem. Thanks again... Steve

You could disconnect the wire at both ends and loop a load through them in different combinations checking voltage drop across the link. Use something hefty like a space heater so the voltage drop was apparent.

Did you check it back at the main? May not be the sub at all.