Service Entrance Cable low voltage

[Bacchus]

I'm helping relatives out because they lost a phase going from their trailer to their panel in the back bedroom 120 ft away. Everything was working great for 2 weeks and all of a sudden one of their phases now only reads 80 volts and phase to phase @ 190

More info:
- Service is coming from a trailer 100 amp breaker near their meter box.
- I tested the voltage reading at the time of installation and everything checked out 100%: 246 volt phase to phase, 123v phase to ground.
- Yesterday tested both wires every way I could, now this:
o 246 volts at main breaker box on line and load. I even went so far as to try the red phase (80 volt) on the left side of the breaker.
o At trailer panel I am getting 123 volts on the black phase and 80 volts on the red phase and 192 volts phase to phase.
o I have everything I can put on the black phase ATM. Everything works except for the hot water heater @240 volts. It has a super saver system which won't run off 190 volts.
o I eliminated the possibility that it's a bad connection that's causing a problem. I even went so far as to disconnect the wires at the panel and tested them separately.
- Ran #2 aluminum USE-2 in the ground. I was going to run a pipe but likely too many bends (I count 6). I did not test the wire out beforehand, but since everything worked before we back filled the trench, I didn't worry.
- Went underground until and trench reached back of trailer, then ran PVC pipe from the end of the trailer 15' away with two 90s to the panel. In retrospect I think I should have dug the rest of the way all the way to the panel. If anywhere there was damage it's likely in there because how it had to be done, plus running with non-electricians.

Experience. I apprenticed industrial/commercial with little residential. Got license and have been using it intermittently in residential and some simple commercial jobs. Mostly lights, receptacles and friends from time to time. This is my first SE job. It's easy right? Run in ground, run to panel, connect, done? right? :/

Is there any way to test the wire as to where the break might be? Something I can rent? I'll be getting a meggar tonight or tomorrow to test the wire. But at this point it looks like I'm going to have to start digging! I can't see how I can get around it. Any advice will be appreciated.

Ron.

 

[readydave8]

I'm tired and so not completely comprehending your situation, but seemed similiar to one I ran in to a while back.

This was a doublewide, to make long story short:

After long troubleshooting process, following many false trails, finally found problem to be POCO bad connection.

Don't completely rely on your volt meter, put a load as close to POCO meter as possible and see if anything changes with voltage readings.

 

[GoldDigger]

I'm helping relatives out because they lost a phase going from their trailer to their panel in the back bedroom 120 ft away. Everything was working great for 2 weeks and all of a sudden one of their phases now only reads 80 volts and phase to phase @ 190

More info:
- Service is coming from a trailer 100 amp breaker near their meter box.
- I tested the voltage reading at the time of installation and everything checked out 100%: 246 volt phase to phase, 123v phase to ground.
- Yesterday tested both wires every way I could, now this:
o 246 volts at main breaker box on line and load. I even went so far as to try the red phase (80 volt) on the left side of the breaker.
o At trailer panel I am getting 123 volts on the black phase and 80 volts on the red phase and 192 volts phase to phase.
o I have everything I can put on the black phase ATM. Everything works except for the hot water heater @240 volts. It has a super saver system which won't run off 190 volts.
o I eliminated the possibility that it's a bad connection that's causing a problem. I even went so far as to disconnect the wires at the panel and tested them separately.
- Ran #2 aluminum USE-2 in the ground. I was going to run a pipe but likely too many bends (I count 6). I did not test the wire out beforehand, but since everything worked before we back filled the trench, I didn't worry.
- Went underground until and trench reached back of trailer, then ran PVC pipe from the end of the trailer 15' away with two 90s to the panel. In retrospect I think I should have dug the rest of the way all the way to the panel. If anywhere there was damage it's likely in there because how it had to be done, plus running with non-electricians.

Experience. I apprenticed industrial/commercial with little residential. Got license and have been using it intermittently in residential and some simple commercial jobs. Mostly lights, receptacles and friends from time to time. This is my first SE job. It's easy right? Run in ground, run to panel, connect, done? right? :/

Is there any way to test the wire as to where the break might be? Something I can rent? I'll be getting a meggar tonight or tomorrow to test the wire. But at this point it looks like I'm going to have to start digging! I can't see how I can get around it. Any advice will be appreciated.

Ron.

Hi Ron,
I will suggest a systematic approach, with some analysis along the way. Some of the alternatives below are improbable, but I am including them anyway for completeness.

1. Measure the voltage at the utility end of the SE if you have not done so already. It should be 120-0-120 or close to that. Check?
2. Put a load of some sort, even just a light bulb, on the red phase at the house and see if the voltage holds constant at ~80 or goes to zero.
If it goes to zero, the 80V you are reading is a phantom voltage from capacitive or inductive coupling and the wire is completely open at some point. You will have to figure out where that happened. If you have a circuit tracer that can sense the wire while buried, use it to find out where the signal goes away and dig there. BTW, the fact that the (phantom) voltage is out of phase with the black wire (123 adds to 80 to get 192) suggests that it is NOT capacitive coupling. Maybe still inductive coupling because it does not add up to ~203 as I would expect if it were a "real" voltage.
If it does not go to zero, continue.
3. If the voltage stays at 80 with the lamp on (dimly) and you still measure 120V at the trailer end, then you do not have just a high resistance in the wire, you have a fault to ground that it pulling a LOT of current but is not tripping the breaker. Be careful not to try digging anywhere near the USE with the power on, because you could get a shock from elevated earth potential. On the other hand, checking the potential along the route by sticking a screwdriver (with insulated handle!) into the ground and measuring voltage with respect to a remote ground (another screwdriver) may help you zero in on where the fault is.
But before you do any of that, check the current in the red phase at the source with a clamp-on ammeter. If it is dangerously high for the wire size you will have to do the rest of your troubleshooting with that wire disconnected.

 

[meternerd]

If you think it's a POCO problem, they'll probably come out and do a load test with a "Beast of Burden" which puts up to 80 Amps on each phase and measures voltage under load. If it's OK, then they are out of the loop. Shouldn't be any cost to the customer.

 

[tek9]

My daughter said,use a thumper,i said yeah,right,forget the thumper,used one of those things once as an apprentice to find a fault in a 33Kv underground cable that had faulted with watertrees,it located the short alright,blew the top off a manhole cover,and ruptured a 400 pair telephone cable installed the week before.The telephone company were not amused,old bean,that's what this Brit told me,he was an employee of Telecom Australia.

 

[Bacchus]

Hi Ron,
I will suggest a systematic approach, with some analysis along the way. Some of the alternatives below are improbable, but I am including them anyway for completeness.

1. Measure the voltage at the utility end of the SE if you have not done so already. It should be 120-0-120 or close to that. Check?
2. Put a load of some sort, even just a light bulb, on the red phase at the house and see if the voltage holds constant at ~80 or goes to zero.
If it goes to zero, the 80V you are reading is a phantom voltage from capacitive or inductive coupling and the wire is completely open at some point. You will have to figure out where that happened. If you have a circuit tracer that can sense the wire while buried, use it to find out where the signal goes away and dig there. BTW, the fact that the (phantom) voltage is out of phase with the black wire (123 adds to 80 to get 192) suggests that it is NOT capacitive coupling. Maybe still inductive coupling because it does not add up to ~203 as I would expect if it were a "real" voltage.
If it does not go to zero, continue.
3. If the voltage stays at 80 with the lamp on (dimly) and you still measure 120V at the trailer end, then you do not have just a high resistance in the wire, you have a fault to ground that it pulling a LOT of current but is not tripping the breaker. Be careful not to try digging anywhere near the USE with the power on, because you could get a shock from elevated earth potential. On the other hand, checking the potential along the route by sticking a screwdriver (with insulated handle!) into the ground and measuring voltage with respect to a remote ground (another screwdriver) may help you zero in on where the fault is.
But before you do any of that, check the current in the red phase at the source with a clamp-on ammeter. If it is dangerously high for the wire size you will have to do the rest of your troubleshooting with that wire disconnected.

Bravo, this did it for me. I found the problem and fixed it.

In summary it was a wire that had melted in one spot. It was the oddest site because 4 inches of the aluminum wire was missing and on the line side it was melted. The insulation was only split wide open and not burned in half like the wire. The only reasonable explanation is the wire had a fault in it. There was no mark on the insulation being hit by anything solid like a shovel.

More information:
- The voltage on the red phase was a phantom voltage. I should have used my wiggy from the start. I do normally but I was @ residential and I have had no problems with phantom voltages with my Fluke 87V, but commercial is another story. The wiggy showed no voltage at all on the red phase at the panel but showed 120v at the main disconnect. A wiggy will always be relevant.
- I tried your suggestion about testing for phantom voltage. I put a load on the red phase and the voltage went to ~zero. Good technique.
- I tested load side of disconnect for red phase @ 0.5 amps with amprobe. The black phase had 0.0 amps. It was relatively safe to work while live.
- I drove a 2 foot piece of all-thread in the dirt to use as a ground. I attached a 30+ foot wire to the all-thread via 5 tight wraps and attached the other end to one of the leads of my Fluke with a clamp lead. After a continuity test, I stuck my 6" screwdriver in the dirt and read any voltage along the wire path from beginning to end. I got about ~2 volts along the trench path. At about 50 feet the voltage started to raise, from ~2V to ~9V for about 10 feet and then returned to 'normal' until the end.
- I returned to that 'higher voltage' spot and drove another 2 foot all-thread into the ground (with tape covering the top) outside the trench zone on an angle and retested it. I was thinking I might get a higher voltage reading but it stayed about the same ~9v.
- We dug at the likely break. Bingo! we found the break. They were happy and as surprised as I was but I tried to keep my emotions in. I was surprised because I was expecting the voltage to be much higher in the ground, possibly 20 or 30v at least. I'm glad I was wrong.

Fix: UL listed underground splice and refilled trench.

The advice was much appreciated. The poor man's tracer worked like a charm.

Ron.

[Edit: I don't know what happened with the previous reply. I only hit reply once. ]

 

[meternerd]

My daughter said,use a thumper,i said yeah,right,forget the thumper,used one of those things once as an apprentice to find a fault in a 33Kv underground cable that had faulted with watertrees,it located the short alright,blew the top off a manhole cover,and ruptured a 400 pair telephone cable installed the week before.The telephone company were not amused,old bean,that's what this Brit told me,he was an employee of Telecom Australia.

A thumper? Those are for direct buried primary cable fault locating. Use it on secondary and you'll blow the $#@& out of it.