256 ° emt with no conductors in it

Status
Not open for further replies.
J

jim gage

Member
Location
longmont Co. Boulder County
I have an issue that is making me scratch my head. I was called to an apartment house of a popping breaker trip on a lighting circuit. I opened the 4/0 oct. Box and found it packed with 21 spliced 12 solid wires and it appeared that one of the wires had pinched to an emt connector and blew up. I replaced all wires in that conduit because of arch damage and pulled and reconnected everything existing with 12 stranded along with addind an extension box to create more space so I did not have to stuff the box so tightly. After redo I turned everything back on and checked all outlets lights etc for function and all was good. The following morning I was called and told is blew up again in the same location and it tripped the same two breakers. I assumed I would find a different problem in the same box due to the previous short circuit damage on some of the wires I thought looked undamaged and that all my work would still be intack but when I returned my new wires were grounded out to the connector and melted and tripped out. I noticed this time that there was extremely high temp reading on the connector that was shorting to the wires. I pulled the bad wires out of the pipe and then noticed the connector was arching to the 4/0 box therfore causing it to heat up to 256° F according to my IR gun. This prompted me to clamp on to the pipe with all breakers off in that units sub- panel and the conduit had 12 amps of current on it even with no power in the apartment panel. I then had my apprentice watch my meter as I cycled all 10 apartment feeder breakers off to see if I could find out where the source of current was coming from and none of them made it go away when off. Then I shut the main down and of course it went away. I tightened the lock rings on the emt and bonded the subpanel can to the neutral and had a fair arch but it cleared the meter from current and stopped the conduit from heating up. When I found that turning the building main off had put the emt current reading to zero I also observed that when I re-energize the main the current reading spiked to 47 amps on the empty conduit and over a brief time returned to the original fluctuating 4 to 12 amps.
What is going on I am wandering if this could be a result of non bonding and ground at the main service 12 bank meter stack. Feeling dumb please advise.
 
It sounds like some type of open service neutral problem with the neutral current current flowing on the raceway and creating heat a the mechanical connections.
But just a guess and it will take some digging to find out what the issue is for sure.
 
I had a few spelling errors I didn't notice before posting but it looks like you got my intended meaning.
I didn't have time to look in to it further because it was 8 pm and totally dark by that old meter stack and the temp bond in the sub-panel seemed to take care of the immediate problems along with tightening the lock rings. Here is hoping it settles the issue until supply houses open up again on monday and I can open things up and check out the service bonding and grounding.
Thanks for your input.
 
I agree with Don, the conduit is serving as a return path. Since it didn’t disappear after each apartment was turned off, but did when the main service disconnect was turned off, it is a little puzzling, unless it’s a ground fault in the wiring to the meter stack. Check the voltages from the conduit to neutral and phases to see if there is any anomalies there.
 
On a troubleshooting job, it will be easier better in the morning.
I agree with Don, a open neutral is likely. It may be there is a ground connection to a metal water pipe which could allow a path for neutral current back to source.
 
Thanks to all for the input.
I was confused about how an empty conduit could have current on it in a apartment that has been turned off at the service gear and while monitoring the current on the pipe it did not go away by dropping power to each individual apartment one at a time. My first thought was a neutral from another unit had failed and was making contact to a conduit using the conduit system as a path back to the service neutral and if I am thinking correctly, wouldn't disconnecting power to that circuit source make it go away?
 
jim gage said:
... This prompted me to clamp on to the pipe with all breakers off in that units sub- panel and the conduit had 12 amps of current on it even with no power in the apartment panel. I then had my apprentice watch my meter as I cycled all 10 apartment feeder breakers off to see if I could find out where the source of current was coming from and none of them made it go away when off. Then I shut the main down and of course it went away.
Click to expand...
hillbilly1 said:
... Since it didn’t disappear after each apartment was turned off, but did when the main service disconnect was turned off, it is a little puzzling, unless it’s a ground fault in the wiring to the meter stack.
Click to expand...
I'm thinking that maybe the OP meant he turned off each apartment feeder breaker one at a time but with the others turned on. If all of them were turned off and the current remained then I agree that's very puzzling.

I agree with Don,etc. that there is probably a break in the neutral, with the neutral bonded both before and after the break so that the EGC's are carrying neutral current.
 
Turning off the apartments were mentioned, but does this complex have a house panel? It was not mentioned. That would explain why the current went away when the main for the complex was turned off, if the fault is in the house panel.
 
jim gage said:
Thanks to all for the input.
I was confused about how an empty conduit could have current on it in a apartment that has been turned off at the service gear and while monitoring the current on the pipe it did not go away by dropping power to each individual apartment one at a time. My first thought was a neutral from another unit had failed and was making contact to a conduit using the conduit system as a path back to the service neutral and if I am thinking correctly, wouldn't disconnecting power to that circuit source make it go away?
Click to expand...
Maybe some of the conduits coming from different apartment panels are bonded together somewhere, perhaps to the building steel they have in common, if not from a mistaken connection of conduits from different apartments. Then a combination of an open neutral and any neutral bonding downstream from this open neutral might cause current coming from breakers in one apartment to flow through conduits in another apartment.
 
I apologize for not mentioning the house panel And 1 additional unlabeled panel with a 2 pole 30 and a single pole 20 in it but I cycled them off as well with no loss of current on the emt. Basically I turned off all feeder breakers from the meter stack and none of them removed the current from the emt until I cycled the Service Main when it was off the current was gone but no individual feeder breaker made any change except for a small spike when turned back on with a couple of the apartments. The current was fluctuating during my time there from 4 to 12 amps and steady at times anywhere from 4 to 6 amps.
When a couple of the apartment breakers were turned of a small drop would occur and a spike of 4 to 5 amps would would occur when turned back on but it would then go back to the baseline of 4 to 12 amps with random fluctuating.
 
I should also mention the feeder breakers were cycled 1 at a time. I was looking for what panel the source of current was coming from. I did not turn all panels off at one time except when I cycled the Service Main. When the Main was turned back on that is when the high current spike occurred at 47 amps.
 
jim gage said:
I was confused about how an empty conduit could have current on it in a apartment that has been turned off at the service gear and while monitoring the current on the pipe it did not go away by dropping power to each individual apartment one at a time.
Click to expand...
Sounds like the neutral current for the entire building.
 
Proved service neutral
Proved bonding
I think we proved meter stack neutral buss
Great, now the fun begins I am thinking this may be a real easter egg hunt now.
Thanks for all input
I will let all know what is found when we know it is remedied.
 
When I returned to begin the hunt for the problem, we started with a feeder conduit wiring j-box due to a high resistance to ground reading from the de energized panel neutral and water pipe in the apartment. Crawled through the nasty attic opened the j-box and found nothing. I crawled out whet down to my service van for a drink of water and did a little more testing at the meter stack . I was sure I would find nothing but did it anyway. I clamped the conduit that had current on it and it was still there of course but it was only 4 amps at this time. At this time I noticed the main was not properly secured to the 1880 brick building and was putting diagonal torque on the connection busses.
Tested neutral to main line voltage in bank 1 meter stack had perfect balance then I tested neutral in bank 2 to main line voltage and this time I had 121v A phase and 123v B phase.
Same one bank 3 meter stack. Bingo light went on just like in the cartoons!
Continued test from bank 2 to line and pushed slightly on the main enclosure and it went back to balanced voltage. Called LPC power they came out and removed meters so I could access buss connection bolts and they were all loose in both section 1 and 2. In my opinion they were never tightened during original installation orver 30 years ago. I got 9 turns out of every one on both sections re-energize gear all issues of unbalanced voltage and conduit current and ground current were solved. Due to observations of arching on A and B phase we have a meter bank and main to replace some time in the near future. Just wanted to say, sometimes even when all things point to a bad piece of service bussing and you cannot find anything wrong with meter testing look around and if something in the install isn't look right just give it a little tug or a shove you may be surprised what you will find after that.
 
jim gage said:
When I returned to begin the hunt for the problem, we started with a feeder conduit wiring j-box due to a high resistance to ground reading from the de energized panel neutral and water pipe in the apartment. Crawled through the nasty attic opened the j-box and found nothing. I crawled out whet down to my service van for a drink of water and did a little more testing at the meter stack . I was sure I would find nothing but did it anyway. I clamped the conduit that had current on it and it was still there of course but it was only 4 amps at this time. At this time I noticed the main was not properly secured to the 1880 brick building and was putting diagonal torque on the connection busses.
Tested neutral to main line voltage in bank 1 meter stack had perfect balance then I tested neutral in bank 2 to main line voltage and this time I had 121v A phase and 123v B phase.
Same one bank 3 meter stack. Bingo light went on just like in the cartoons!
Continued test from bank 2 to line and pushed slightly on the main enclosure and it went back to balanced voltage. Called LPC power they came out and removed meters so I could access buss connection bolts and they were all loose in both section 1 and 2. In my opinion they were never tightened during original installation orver 30 years ago. I got 9 turns out of every one on both sections re-energize gear all issues of unbalanced voltage and conduit current and ground current were solved. Due to observations of arching on A and B phase we have a meter bank and main to replace some time in the near future. Just wanted to say, sometimes even when all things point to a bad piece of service bussing and you cannot find anything wrong with meter testing look around and if something in the install isn't look right just give it a little tug or a shove you may be surprised what you will find after that.
Click to expand...
Frustrating. Glad you found it
 
Pictures would have been amazing !!! I had one house with 3 amps on the copper water main. Even with the main off. Never found it, never will. Something on the POTS, somewhere in the neighborhood.
 
Status
Not open for further replies.
Top