The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
Live Chat Feature
by Admin
40 minutes 47 seconds ago
Safety at heights?
by gfretwell
Today at 07:16 PM
failed home inspection.
by gfretwell
Today at 07:03 PM
Webmaster > Admin
by Admin
Today at 05:49 PM
Old Bath Fan
by gfretwell
Today at 01:38 AM
New in the Gallery:
Desk-mounted "power-board"
Top Posters (30 Days)
Admin 33
HotLine1 21
Ruben Rocha 16
gfretwell 15
Trumpy 13
Who's Online
1 registered (Admin), 0 Guests and 184 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#181382 - 10/06/08 09:08 AM Voltage problem
sparkync Offline

Registered: 10/17/02
Posts: 811
Loc: NC
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

Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#181383 - 10/06/08 09:39 AM Re: Voltage problem [Re: sparkync]
Sandro Offline

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
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.

#181387 - 10/06/08 11:02 AM Re: Voltage problem [Re: Sandro]
maintenanceguy Offline

Registered: 12/02/01
Posts: 303
Loc: Southern NJ, USA
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.

#181429 - 10/07/08 02:07 PM Re: Voltage problem [Re: maintenanceguy]
gunther Offline

Registered: 09/17/03
Posts: 59
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.

#181431 - 10/07/08 04:04 PM Re: Voltage problem [Re: gunther]
EV607797 Offline

Registered: 10/25/06
Posts: 756
Loc: Fredericksburg, VA, USA
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."

#181434 - 10/07/08 05:13 PM Re: Voltage problem [Re: EV607797]
electure Offline


Registered: 12/24/00
Posts: 4229
Loc: Fullerton, CA USA
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.

#181439 - 10/07/08 07:28 PM Re: Voltage problem [Re: electure]
sparkync Offline

Registered: 10/17/02
Posts: 811
Loc: NC
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

#181441 - 10/07/08 07:44 PM Re: Voltage problem [Re: sparkync]
gfretwell Offline


Registered: 07/20/04
Posts: 9065
Loc: Estero,Fl,usa
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

#181442 - 10/07/08 08:47 PM Re: Voltage problem [Re: gfretwell]
leland Offline

Registered: 08/20/07
Posts: 856
Loc: Lowell area, Ma. USA
Did you check it back at the main? May not be the sub at all.


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals