The picture shows a commercial building with a gutter and two meters. The gutter drops to each meter/main and on the left side is the circuit panel that feeds sub panels inside the two buildings. The tenents in building A have complained and I have varified that their voltage drops considerably and their computers shut off. This might happen 2-5 times a week. When I tested, I saw the voltage at 100V. I then went to the inside subpanel and tested several times however each leg was 120V and the screw side the the breakers was good too. I tightened all the neutrals I could opened the panels and checked for anything loose but didn't see anything. What I did notice was the other meter/main (Left side) had a burning hot spot . That meter/main is connected to the subpanel on it's left with a small chaise nipple. On both sides of the chaise nipple where the lock nut tightens against the panel there were at least one glowing hot spot that came and went every so often. I did have the power company come out and do a through inspection of their side and they said the voltage was steady. I may have been a bit permature in doing that but I was out of ideas. I would appreciate some other ideas on what to check before I go out there next.
Let me know if you need more information.
Many thanks, Byron
edited to add picture
[This message has been edited by electure (edited 06-23-2006).]
I ran into a similiar situation years ago. Low voltage condition intermittently at some receptacles in one of three shops.
What my problem turned out to be was some prior electrician had bonded the grounded and grounding conductors to each sub-panel via installing lugs and bolting them to the main disconnect enclosure, rather than installing a single bus with enough openings for all the conductors.
The neutral current flow would depend upon the connection to the enclosure for low impedance. I see the parallel with yours in the "burning hot spot".
I fixed the problem by replacing all the lugs with multi-opening bus, and connecting all enclosures together with a copper bonding conductor, directly connected to each grounded and grounding conductor.
POCO, may have only checked thier side of the equipment, most wont go any further. "NMJ" But wise to rule it out...
"prior electrician had bonded the grounded and grounding conductors to each sub-panel via installing lugs and bolting them to the main disconnect enclosure, rather than installing a single bus with enough openings for all the conductors."
Nothing wrong with that... So long as ground on ground bar, and neutral seperate in main panel, and bonded there, even in multiple services.
Anyway, I'm lost as to what feeds the affected area? But either way it sound to me that the panel on the left is either carrying load or fault current on the ground. This is a potentialy dangerous situation if left to continue for any period. In my professional opinion, it should be shut down until located. As it is a high fire or shock risk.
You could locate this a few different ways...
The hot spots are resistive, and creating heat due to current flow, but only a symtom of the real problem. But will need to be corrected any way. Don't fix this yet, it will aid you in locating the fault.
By now the whole kit and cabootle of the affected panels should be off.... Not kidding. Wait for the hot spots to cool! If they don't you have other problems, like current flowing out toward branch areas = BAD! (Bigger problems - loss of GEC, and the system found a better one for you...) If they do cool off... Attach a solidly connected insulated #6 between the panels with the hot spots, or better between the the best grounded portion of the panels closest to the GEC, and the other side of the affected panels. Then turn breakers on one at a time, and then back off while checking amperage on that #6 you installed. The one that gives you an amperage reading jump is the fault, if all of them give an amperage reading to some degree, the neutral is toast. Or a ground and neutral are connected down the line, and this is parralel current coming back.
I'll opt for neutral is toast! (with secondary screw up's.)
Good luck, but get on it quick.....
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: Loose neutral?#66980 06/24/0607:18 AM06/24/0607:18 AM
Perhaps I did not make myself clear. In my case, the neutral current was flowing through the main enclosure, through the equipment, and then back to the transformer. There should not be any current flow normally through the locknuts on your conduit. Only in fault conditions. With normal voltages sometimes, and low voltages other times, I'm guessing a high resistance neutral connection somewhere.
Well I have been reading post hear for almost a year but never given my thoughts. This one I will put my 2 cents in. Last fall I got a call from a Handy man that I do electrical work for he told me that the house he was working on had a bad GFIC in the grudge and when he replaced it half the house lost its power. I went over tested power at plug got a low volt reading I went to meter got same on one side of main checked buss coming from meter and same low volt. I called POCO they came out and found power to meter was fine I told them meter must be bad they pulled meter I looked in and seen the buss had been burnt look a little farther and seen were the manufacture left out the bolt that connects the meter socket to the buss we clean it all up and put in a bolt.This house was about 25 years old. I was amazed it lasted that long with the two metals just touching. So what I want to say is check all connections by manufactures as well as others. Cal
Re: Loose neutral?#66983 06/26/0611:26 AM06/26/0611:26 AM
Quick update: POCO went out there and put their testing equipment on the load side of the meters and left it for a couple days. They said it varied only 2 volts.
I went out there today to check on a few things. I only looked at one meter/main the sub panel to it's left and the three sub-panels that are fed on the inside. I did find a neutral that was loose in one of the inside sub-panels. I figured this was it. I then opened all panels and tightened everything. I then checked my voltage at a few outlets. I found that the voltage was high this time (128); a problem the tenant told me about. Infact he said if it wasn't around 100V it was up around 140V. Still collecting data, I decided to check the meter/main case to the sub-panel case it fed to the left. I got around 30V. I then decided to shut the sub-panel breakers off (all of them) and test the ground to the load side of those breakers. Again, around 30V. Finally, I decided to shut the meter/main off and test it's case to the sub-panel case; around 30V. The one thing I did notice is there isn't a good bond between the meter/main case and the sub-panel case. They rely on a chase nipple and lock nuts. I know to neutralize the case to case voltage I could put in a bonding jumper, but this doesn't fix the real problem. I did examine the GEC and it seemed to be in fine shape. The wire went underground so I couldn't see if there were any further problems with it.
I've said it, Reno said it again, I'll say it again... "The "burning hot spot" says it all. Kill it NOW!
The two cans should NOT be carrying current! This is NOT a time to be collecting data in a situation like this. A high/low voltage problem is indicative of a lost neutral, and should not be left in this manner for any amount of time...
We can not go troubleshoot it for you, but it is obvious that the neutral is gone! And it sounds like a second connection of the grounded conductors (Neutrals) to the ground(s) of the sub-panel.
I hope your liability insurance is top notch.... The joint could be on fire right now, some items react that way with the voltages you've described.
Heres a simular example . Ignore the roaches and needle containers, focus on what happens when a ground becomes a current carrier, and choosing paths on its own.
Mark Heller "Well - I oughta....." -Jackie Gleason
Byron, I am somewhat baffled that, as a licensed EC, you don't seem to feel a bit of urgency in the fact that you're describing a metal box and fittingGLOWING RED HOT!! It's simple to figure out that you've lost a neutral somewhere downstream (It's not the poco's issue if they already checked their side under load,) and current is finding a HIGH impedance path back to the main service. I certainly hope no one bumps their arm on that service and gets nailed !!
SHUT THE POWER OFF!!! If you can't find an obvious place where the neutral/ground are being tied together, other than at the main service point, then turn all the branch breakers off, disconnect your neutral feeders to the subpanels at the main service disconnect and ring them out to ground. (Open noodle test) You shouldn't get anything. Likely from your described scenario, at least one will give a reading.. Follow it until you find the point downstream where it has faulted and/or been tied together with your grounding. (a toner might be helpful here incase the wire itself might have failed underground)Follow it from point "A" to point "B". If youre lugs were tight and not corroded at each end, you'll find it along the way with the toner when you lose tone.
I might also suggest replacing the parts that became "burning hot", and even though it may not be required, pull a properly sized ground wire to help eliminate "glowing fittings" should another fault occur down the road. You stated you found loose fittings here and there... It's an easy "peace of mind".
Of course, this is all dependant on your jobsite not becoming a "Structure Fully Involved" call to your local fire department before you decide to lock the power out!!
I did mention shutting the power off to the owner of the complex and she flipped. Believe me, I have expressed the importance of getting this fixed but she says it has been going on for over a year and she seems to be more interested in tenents paying rent and being happy. This problem is noticed by only one tenant. She only hired me about a week ago to check it out. I'm not sure how many electricians have looked before me. You know how that is.
If I shut off the both meter/mains and then go from the case to the water/ground below and get a reading of 30Amps don't you think that should be POCO's problem??