Need ideas

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Ebow

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I need some second and third opinions on this please.

Went on an after hours service call the other night to a sprawling apartment complex. The building I went to had twenty-four apartments with two 800 amp mains (twelve apts. per main) one of the mains had been tripping and every time they reset it, it would trip again in a few minutes (maint. guy said about two minutes). When I got there they had the door open and the main reset after about thirty minutes of off time. I looked it over and saw no physical problems everything nice and new looking as it was just barely a year old. A quick check with the thermal thermometer showed that L1 was running about 20 deg. F hotter than L2. I tried to do an amp check but with three paralell 500's it was not easy and I am sure not accurate. I left an hour later and the main was still holding and the block temps had decreased as had the ambient (92 deg F to 86 deg F).


I figured there must be a loose connection somewhere on L1 either at the breaker lug or in the meter bank. Anybody got a suggestion as to what else it might be?

Gene
_______________________________

Remember - Speed Kills and its not always you.
 
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
I would look again at the termination to the breaker itself. Use a flashlight. I would also look to see that there are not more splices on one of the legs, causing an imbalance. you mention the temperature was high. Has the tripping been occuring when the temperatures are higher? A/C usage may be an issue, causing overloads. Just guessing outloud.
 
quogueelectric

quogueelectric

Senior Member
Location
new york
Check the depth on all of the set screw comp lugs that they are all the same depth and look for discoloration. You are just wasting time without an acurate amprobe reading. Get the right test equip and check the amperage.
 
P

Power Tech

Senior Member
Location
Lebec, California
Ebow said:
I need some second and third opinions on this please.

Went on an after hours service call the other night to a sprawling apartment complex. The building I went to had twenty-four apartments with two 800 amp mains (twelve apts. per main) one of the mains had been tripping and every time they reset it, it would trip again in a few minutes (maint. guy said about two minutes). When I got there they had the door open and the main reset after about thirty minutes of off time. I looked it over and saw no physical problems everything nice and new looking as it was just barely a year old. A quick check with the thermal thermometer showed that L1 was running about 20 deg. F hotter than L2. I tried to do an amp check but with three paralell 500's it was not easy and I am sure not accurate. I left an hour later and the main was still holding and the block temps had decreased as had the ambient (92 deg F to 86 deg F).


I figured there must be a loose connection somewhere on L1 either at the breaker lug or in the meter bank. Anybody got a suggestion as to what else it might be?


Gene




I had a situation where the screw from the factory connected to the bussing. The screw welded the threads and could not be tightened. Had to get a new main breaker. Sounds like something is loose but you do need to get a good FLA reading. Also the time of day may give some clues.
Click to expand...
 
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e57

e57

Senior Member
Location
San Francisco, CA
Yeah should have chucked a clamp on it and hung around a little - the thermometer however can be good qick way to located any loose connection IMO. But won't tell you what is actually happening.

That said - there may have been something happening down the line on the load side that was being the 'straw that broke the camels back' so to speak... 12 apartments on 800a - gives no indication of how loaded they all were... Somebody may have decided to sneak in a hot tub install, and that same person may like the AC on too - while in said hot tub. Who knows???
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Rewire said:
You did not mention what type wire was used aluminum has a tendancy to "crawl' and can create a bad connection.
Click to expand...
That is most commonly caused by excessive termination torque on the original installation or being re-torqued after the original installation. It is not normally an issue if the connector was designed for aluminum conductors and it was installed with a torque wrench.
 
Rewire

Rewire

Senior Member
Location
Lake of the Ozarks
don_resqcapt19 said:
That is most commonly caused by excessive termination torque on the original installation or being re-torqued after the original installation. It is not normally an issue if the connector was designed for aluminum conductors and it was installed with a torque wrench.
Click to expand...

I think to often termonals are "feel" tightened
 
E

Ebow

Member
Thanks for the input. You have all pretty much validated what I suspected from the beginning. Some things you mentioned that had caught my eye but had not mentioned -

Wire was aluminium.

Lug set screws were all tightened down to different depths on the block.

There was not any obvious signs of discoloration but in pale evening light with a flash light for back up it could have been missed if it was slight.

A new tenant had moved into one of the apartments that day.

And yes as I stated it has been hot. The high temp for the day had been 96+ and the electrical panel and meter array were on the west side of the building. All the a/c units were running while I was there and more than likely been running all day if not all night being as the night time temp only gets to the low 80's.

The problem with checking the amperage was the three paralelled lines, all I could do was check them individually. Add them together and come up with an estimated amperage. Even using that method the amperage on L1 would have been about 230 and L2 about 210.

Gene
______________________________________

Remember - Speed Kills and its not always you.
 
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