[Bythepond88]

The circuit breaker to my detached garage kept tripping. I traced the problem to an improper splice in the underground cable from the house to the garage. I fixed that with an underground approved splice kit. I double checked with a simple test light after the repair, and had power to the ends of the cable. But when I hooked the cable up to the garage wiring, nothing worked. I touched the test light to splices between the cable and garage wiring, and no light. Oddly enough, if I touch one lead of the test light to the common wire, there is a faint glow that goes out when I touch the other to the power wire.

The breaker does not trip, but there is no power when connected to the garage wire.

Apparently, there is a problem in the garage wiring (everything worked fine before the splice shorted out). Do these symptoms ring a bell with anyone. Any suggestions as to what to look for, other than to just disconnect the branch circuits in the garage one by one and track it down that way?

 

[mako1]

Could be as simple as a bad ground.Start with the lowest common denominator and a meter .Not a test light.Also double check the last change in the system which would be your work.

 

[sparky48]

So as I understand what you're saying, you have power to the garage from the wire that you repaired. If that's the case and nothing works when you hook it up to the original wiring of the garage, leave that wire detached and start taking everything apart in the garage. Somewhere there is a problem with the garage wiring. Could be a bad splice in a box, a staple that has comprimised the insulation on the NMB if that's what was used. You basically have to check it all. If you have a multi-meter that would be a BIG help over a test light. If you have one, set it on the OHMS setting and start ringing out the wires.

 

[Bythepond88]

Well, I started out by disconnecting wires, as Sparky said, but it seemed that every circuit with a switched load would drop the voltage to zero. Then, on a whim, I used the test light on an outlet, and it showed power, but when I plugged in a lamp, the lamp wouldn't work, either.

So I went back and disconnected the feed to the entire garage and hooked up the multimeter to the feed cable wires. I'd done that to begin with, and got a reading of 115v. This time, however, I kept the meter attached and watched the readings. Although they wandered up and down, on the whole, the readings were steadily decreasing from the initial 115v, to 100v by the time I stopped.

I went back to the breaker box, and took a reading from the power pole on the breaker to the bar where the common wires connect, and got a reading that hovered around 124v. So now I'm thinking that there's still a problem in the feed cable, maybe I didn't do the splice quite right.

Does that make sense?

 

[bob22]

Seems like the likeliest spot for a problem if the feed source is solid.

 

[sparky48]

May I ask how you found the broken wire in the ground? It's beginning to sound like there may be another compromise underground somewhere.

How far is the run from the house to the garage? Did the garage circuit ever work properly, or is this something that just started?

I surely can't understand why the differential in voltage in the garage. If you start with 115v it should remain at that. Being you have 124v in the house, the distance of the run could contribute to a voltage drop in the garage. But the fluctuation shouldn't be happening. What size conductors are involved in the run of wire?

 

[AllanJ]

Likely situation is a rusted out wire in the feed. Are the underground wires aluminum, which could rust out not so slowly if the insulation had biodegraded and cracked.

May be at the same place where you made the splice but not guaranteed.

The rusted out remains mixed with dirt could sizzle and change resistance from minute to minute or second to second as you have your meter or a load connected thus you might see a variation in voltage before your eyes.

 

[sparky48]

I've never heard of copper or aluminum rusting. That's a new one on me.

 

[Bythepond88]

Update on the situation.

In answer to Sparky, the run from the breaker box to the garage is 40-50 feet, and is 12 gauge solid wire.

I recently moved to this house, and when I moved in, everything in the garage worked fine. The way I found the underground problem is that originally, the garage was wired to the same circuit as the back door light. As part of my troubleshooting when that light stopped working, I disconnected the garage from the circuit, and that circuit breaker stopped tripping.

I started digging up the cable to the garage, and found the bodged splice. I used an approved underground splice kit, and then added a new junction box in the crawlspace and added a separate circuit for the garage to the breaker box.

You are correct that the cable is compromised in addition to the bodged splice. After I noticed the voltage anomaly, I cut apart my new splice (I wasn't going to bury it again until I knew everything was working), and did another check at the end of the cable from the house, and found the same dropping voltage, albeit it wasn't dropping so quickly.

Further investigation is needed, and I will report back what I find.

 

[Bythepond88]

Re: Garage electrical problem - Solved!

Sorry for not posting back earlier. I climbed back into the crawlspace and discovered that there was indeed another splice and the common wire connection had come apart. I guess there was enough wire in the circuit for a microcurrent to get through, which is why I was getting a voltage reading. I'm also guessing that as that wire "filled up," it caused the voltage to slowly drop.

So I didn't have to undo my original underground splice, but that was a blessing in disguise, because I now realize that the cable running from that splice was regular NM, and not suitable for burying. (Up to that point, it was UF) So I replaced that run with proper UF cable.

Anyway, the lights are on again in the garage. Thank you all for all your help!

Next issue is that the cable from the house is only two conductor, with no ground wiring, but I'll start a new post regarding that.