O.T. Electrical Quandry

[George Summers]

The electrical drop (220V) for the shop comes off a breaker by the meter box of the house. The line runs underground, through a conduit, to the box in the shop. Three days ago I was in the shop working with no problems. I went out yesterday and the saw nor the DC would start (both are 220V). After much checking: the voltage at the output of the breaker at the house is 220V, the voltage at the same two wires coming into the box in the shop is approx 150-160V (hard to measure on the 600V scale on my multimeter - it softly pegs on the 150V scale). All 110V outlets in the shop read 110V. The two 220V outlets in the shop read 150-160V (same as the output of their respective breakers and the incoming voltage to the box). I have flipped all breakers several time. I have thrown the breaker out of the meter box and pulled all the breakers in the shop box. All contacts look good and not burned or discolored. All screws have been tightened.

How can one end of the feed read 220V and the other end of the same line read 150-160V. Please tell me what to check so I don't have to call an electrician tomorrow.

George

[Kevin Gerstenecker]

Goerge, what are the 2 Hot Conductors reading when you place one meter probe on the Hot Conductor and the other probe to ground, or neutral? You want to take this reading on the Lugs in the panel, where the feeders from the house connect to the sub panel in the garage. You should be getting approx. 120V on each leg in the panel. Of course, you should also be getting approx. 240V between the 2 Hot Legs also. Check as mentioned above, then check the load side of your breaker to see it it is the same.

[George Summers]

I have continued to check. Conduit is continious PVC. All installation (four wire) was done by an electrician three years ago. At the shop end: one feeder to hot and to ground is 110V, other feeder to hot and to ground is approx 25V. Looks like a problem in that one feeder wire but I still don't understand why or how. I have called the electrician who installed it.

George

[Paul Kunkel]

I have continued to check. Conduit is continious PVC. All installation (four wire) was done by an electrician three years ago. At the shop end: one feeder to hot and to ground is 110V, other feeder to hot and to ground is approx 25V. Looks like a problem in that one feeder wire but I still don't understand why or how. I have called the electrician who installed it.

George
Check to make sure that both the ground (bare wire) and the neutral(yellow stripe usually) are connected good at both ends. Sometimes a little corosion can cause the connection to fade.

[Ron Meadows]

George,

It sounds to me like the breaker in the panel at the house has pooped out. Kick the main breaker on your house and pull it out and replace with another one.

Only other thing that I can think of is that you have developed corrosion in the connection for the offending hot line. With the power turned off take each end of the offending wire out and look for oxidation. I know that you said an electrician did the work for ya, but maybe he forgot to add the compound that keeps the aluminum wire from corroding the copper lugs. Electrolysis occurs at this junction rather easily between the dissimiar metals.

Ron

[Steve Clardy]

If you check your connections as Paul suggested and all is well, you may have a wire burnt underground. Hope not, but-----Steve

[Mac McAtee]

Meanwhile I wouldn't run any 220v equipment even if it will turn over and start. You could burn up a motor. I'm sure you know that but can't help but put my oar in the water.

[George Summers]

Paul, Ron -

Re: The Corrosion Idea: If one feed is 110V between the feed and neutral and between the feed and ground, wouldn't that show that the neutral and ground are corrosion free?

Re: Bad breaker at house end: Still get full 110v on all 110V circuits in shop. Wouldn't some be off if breaker bad?

Re: Alum wire: House only has Alum wire in it (old house built when they were experimenting with alum wiring). The new box the electrician put in is what they call in NC, a mobile home box. Mounts to outside of house, feed comes from the pole to the meter (mounted to the box) to breakers in the box, in my case one breaker feeds through to the main house panel and one feeds underground to the shop panel. House wiring would have no effect on the circuit to the shop.

George

[Steve Clardy]

My neighbor down the road 1/2 mile had the same problem at his house three years ago. I went down with a meter and it checked exactly like you first described your problem. No 220 in the house, just 110 on one side of the inside box. Water heater, ac would not work. Did a little digging and found the alum. wire corroded and broke almost completely through. There was just enough connection to get 20-30 volts to show.
He rewired, conduit and all underground and fixed the problem. Next year had the same problem after an electrical storm, burnt one wire in to.
So I think maybe you have a wire broken, corroded, or maybe a rodent chewed through. Yes, rodents do chew through plastic conduit.
Hope I'm wrong here as the electrican will probably have to dig it up if he cannot get new wires pulled through. Steve

[Rob Russell]

Re: The Corrosion Idea: If one feed is 110V between the feed and neutral and between the feed and ground, wouldn't that show that the neutral and ground are corrosion free?


Yes.




Re: Bad breaker at house end: Still get full 110v on all 110V circuits in shop. Wouldn't some be off if breaker bad?


Again - sounds reasonable.




Re: Alum wire: House only has Alum wire in it (old house built when they were experimenting with alum wiring). The new box the electrician put in is what they call in NC, a mobile home box. Mounts to outside of house, feed comes from the pole to the meter (mounted to the box) to breakers in the box, in my case one breaker feeds through to the main house panel and one feeds underground to the shop panel. House wiring would have no effect on the circuit to the shop.


You're correct that the house wiring on another panel won't affect your shop feeders.

Some things to check. If the shop was wired 3 years ago, is the wire that the electrician pulled "wet location" rated? That would make it THWN or similar. If it's straight THHN, you could have a crack in the jacketing/insulation and a voltage leak. One way to check that it's a bad conductor is to switch the conductors on the supply breaker terminals. Note - if the problem disappears, you should clip and reterminate with a fresh end and properly torque the connection. Over-torqueing the connection is as bad as undertorquing it. I learned this recently - breakers et all have fairly specific torque settings based on the cycle of wires heating up and expanding, cooling off and contracting. With an external box, you'll be subject to a wider range of temperature fluctuations and more potential of loosening up the connections.

Rob (unlicensed, amateur, homeonwer electrician)

[George Summers]

New Update So You Know The Outcome

I was wrong on one count. The line was not in conduit (old age and memory, you know). One of the hot conductors was on small rock and chafed through the insulation. The voltage kept dropping until it hit zero on that leg by the time the electrician got here. He dug it up and 12" of the line had vaporized, just plain missing. He said that he sees this about 2-3 times a year on the farms in the area with cable running to the out buildings. Has a neat instrument that told him, within an inch, where the wire was open so we didn't have to dig up the whole trench. It could last another three years or another forty years.

George

[Kneale Brownson]

I had the same thing happen to the underground lines to my barn from the breaker in the house panel. They'd been buried maybe 15 years when the power to the barn just failed. When I dug it up, I found about a foot of missing wire on the two hot leads and a damaged insulation on the ground wire. Even though it was wire rated for burial, it apparently had developed a damaged insulation and then grounded to ground. The remaining ends showed burns. When I reburied it, I put it in Schedule 40 (sewer) piping. The barn is 30 years old, so the replacements probably are safe in their conduit.

[Matt Meiser]

Wierd. This morning I read this thread and then went downstairs. A few minutes later my wife said the power was out. We figured it probably had something to do with the events of last week since we didn't get power back until Friday evening and Detroit Edison is asking people to conserve.

Anyway, after a little while I figured we should switch to the generator so I went in and turned off the main breaker. It didn't feel right, so I pushed it back on and the lights came on. Didn't really think much of it, I figured maybe it wasn't seated right or something and tripped off. Then I went out to mow the lawn and found out the lights in the garage/shop were out. I went back in and found that breaker (100A) also tripped. When I turned it back on and went out, I discovered that I had no 220 service and only 1/2 of the 110 stuff worked.

I pretty quickly figured out that exactly the above had happened, only in my case the melting wire also buned through the adjacent line and shorted line-line resulting in blown breakers. It looks like we maybe nicked the line doing a landscaping project earlier this year and it finally gave out, judging from the location.

That was at 10AM this morning. A trip to Home Depot, $100, and many hours of work later, everything is back up and running, this time in PVC conduit and properly buried rather than 6" below ground. We finished up right about dark. All that's left is some cleanup work in the landscaping. and I need to caulk and paint the new conduit at the service entrance.

Good thing for SMC or I would probably still be figuring out what happended!