Humming then main trips

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AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
I have a job that is associated with a previous post I made. I need help turned into something I was not expecting.
I was called for a 200 amp main tripping in a heated storage unite complex. They say it has been tripping for 3 months when the temps get in low 30’s. They wanted me to change the main out cause they thought it was going bad. I asked them if they added any new loads or if something has changed, they said no. I could not see if the breaker was overloaded when I was their. I was planning on popping out late at night when it got cold again.
I I told them you might be overloaded and will have to go to 400 amp. This complex’s has multiple services all 200amp 120/240. They insisted to just change breaker and it’s not overloaded.

I got the PO to come pull meter then we found the neutral almost blown apart.Main breaker was striped out. I jumped to the conclusion that this was the problem, at the time it made sense.

slaped a new 200 square d homeline meter main up last night. Got it powered up today. Flipped the breakers on and a humming noise starts. Every load came on, they sat all night with no power so they were all cold . Checked with my amp meter and it was reading 180 and bang main tripped.

I usually use CH but wanted to try square d.So the main breaker has 4 copper wires feeding the200 amp main. I can only get the clamp in between the end wires. phase a is drawing about 40 amps more than b. Though when I try and check the other phase a it only reads a fraction. Since it’s in the middle of the breker would it not read it correctly since i am not fully seating the wire and any cancelation from other phase. It feels warmer also. I am charging my thermal camera to check it out
Latter.
Is the humming i hear from the large load .if I turn any large load off it dies down a lot. The squad d panels allowed me to fish the conductors behind the panel so it looked neat and it would actually fit.

The meter main feeds three sub panels and a lot of their breakers and buss are correded.
My biggest concern is that that the 200 amp breaker wires got damaged somehow When I got my Conductors behind the panel. I checked when installing and the back side was completely smooth.
I left cause I need to think. I turned off a few heaters so they can atleast have lights. The connection to the main were not tourqed correctly from factory, I corrected. could I have a lose connection on my high reading a phase in the meter section?
Any help will be appreciated. Attached are some picture of the blown out panel and the new on
 

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Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
I would check the service wires to the main breaker with a megger.
Are any breakers in any of the subpanels tripping?
What size breakers are feeding the subs?
Have you checked the loads on the subs with a meter?
 
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
no other breakers tripping. The breakers feeding the subs are 2- 125 and 1-100 . Then the meter main also has 60 amp breaker. I thought when I first got their it was overloaded. Though I can’t get in the heater rooms and read the unites. If it is overloaded how come it worked for 13 years just luck I guess. And it passed inspection also. I will try and and get power company to come back out and pull meter so I can insulate test wires.

How would you approach it. I wanted to do check it out more but they said we will try the breaker and work up from their. Should I say I need to load calc these and size appropriate. Then say just cause it was working dnot mean it was properly sized.
This is my first issue we’re I kinda feel I jumped the gun when he saw the issue in the old panel.

Also wanted to mention. These heater don't run more than 3 hours so I did not consider continues loads. The only thing running for more than 3 hours are out side lights which are about 20 house hold cfl bulbs. I went to the power company and asked them what the peak demand was and they said 180 normally 160. So sinced they don't run more than three hours i thought we were fine.
 
Last edited:
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Since I can't edit my page anymore. Was I Wrong to assume Non Continues. 220.51 heating load shall be calculated at 100 percent. 424 address 125% for branch circuit sizing.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Try not to ass-u-me anything.
Under normal circumstances the heater loads most likely will not cycle at the same time. You turned them all on. The peak the POCO gave you could be a 15 minute time frame. The new meters allow our POCO to send us a graph for a complete billing cycle which would help to determine if this has been a long term issue which is finally rearing it’s ugly head.
 
StarCat

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
Wow.
Is this Electric Heat you are dealing with?
All of those loads need to checked in detail to be sure they are running as they should and there are no problems.
Electric heat, depending on the type can develop some large problems. Many caused by hack job repairs.
I have seen things like one element in a FCU cycling on high limit with no thermostat call, and the heat wire never failing.
This guy was complaining of high electric bill. I have seen all kinds of configuration and wiring errors that will cause problems with Electric FCUs.
As was noted when your main goes down, you lose all your diversity. This is major on all electric heat subdivisions and so forth.
I would go and verify all units are running correctly one at a time and then decrement some of the load if possible at individual heating units to buy some time.
 
kwired

kwired

Electron manager
Location
NE Nebraska
The evidence in your pictures of arcing, especially around what appears to be a bonding screw in grounded bus bar, tells me there has been ground fault current and that screw connection apparently was weak enough it couldn't carry the fault very well.

You might have some load that takes a little time after it is energized before it goes into full fault mode, maybe thermal expansion/contraction are a factor in whatever is faulting. A little odd you don't also have a branch circuit/feeder breaker tripping on affected circuit as well, but definitely getting into the trip curve of the main breaker when this fault happens.

Maybe at very least turn all feeders/branches off, reset the main then turn one circuit on at a time but wait a bit between turning each one on to see if you can narrow it down to one feeder/branch that has the fault.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
I'm with Kwired, sounds like a electric strip heater, The units are probably all the same kw, so amp them all out and see if one is being a pig, or maybe unbalanced due to a fault to ground.
 
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
One thing has me worried For the main breaker .Would the clamp on meter not read the same for the second wire on phase A. I can’t get a complete grip around it and was wondering If phase B magnetic field would be messing with that since i cant get good separation in that section. It shows only 50 -60 amps when the other phase shows 180. I should be reading a equal between the two. some connections were lose and from factory. It’s going to be hard for me to get the PO out. They are supposedly closing for this corona epidemic.

when I take a thermal image I should know more.

something Is unbalanced though cause phase A and B are about 40 amps different. I think I narrowed It down to at least one sub panel
 
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Okay thank you guys for your help. One more question. I feel I kinda messed up assuming that the burnt neutral and striped screw on old buss for 200 amp was the cause. If You guys came to this situation and saw these issue would you do a service change. Or would you do a load calculation on site. I was going to take amp readings if changing the new 200 amp breaker would of not fixed it. Then I saw the burnt issues. All Equipment is locked in different rooms and manger does not know all the location. Been bugging me all night.
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Can you get the amp clamp around the neutral wire that feeds the main's neutral bar? The amount of neutral current there would indicate how much imbalance there is between the phase A and phase B currents.
 
kwired

kwired

Electron manager
Location
NE Nebraska
synchro said:
A QOM-2 200A breaker would require at least 2 times the rated current (i.e., 400A) to trip in 1 minute. And at least 300A to trip in 2 minutes. I expect Homeline to be similar but I haven't checked.

Click to expand...
I was going to say something similar - still think there is a ground fault and it is delayed for some reason before it happens. 180 amps on 200 amp breaker should hold indefinitely, or at least until some deteriorating condition contributes to it tripping
 
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