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Voltage problem #181382 10/06/08 12:08 PM
Joined: Oct 2002
Posts: 830
sparkync Offline OP
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

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Re: Voltage problem [Re: sparkync] #181383 10/06/08 12:39 PM
Joined: Dec 2001
Posts: 444
Sandro Offline
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.

Re: Voltage problem [Re: Sandro] #181387 10/06/08 02:02 PM
Joined: Dec 2001
Posts: 300
maintenanceguy Offline
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.

Re: Voltage problem [Re: maintenanceguy] #181429 10/07/08 05:07 PM
Joined: Sep 2003
Posts: 60
gunther Offline
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.

Re: Voltage problem [Re: gunther] #181431 10/07/08 07:04 PM
Joined: Oct 2006
Posts: 745
EV607797 Offline
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).


"But the guy at Home Depot said it would work."
Re: Voltage problem [Re: EV607797] #181434 10/07/08 08:13 PM
Joined: Dec 2000
Posts: 4,287
electure Offline
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.


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.

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.

Re: Voltage problem [Re: electure] #181439 10/07/08 10:28 PM
Joined: Oct 2002
Posts: 830
sparkync Offline OP
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

Re: Voltage problem [Re: sparkync] #181441 10/07/08 10:44 PM
Joined: Jul 2004
Posts: 9,577
gfretwell Offline
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.

Greg Fretwell
Re: Voltage problem [Re: gfretwell] #181442 10/07/08 11:47 PM
Joined: Aug 2007
Posts: 853
leland Offline
Did you check it back at the main? May not be the sub at all.


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