7 Breakers tripping

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Natfuelbilll

Senior Member
Please help list the things to look at to help investigations into why 7 breakers are tripping at the same time.

Some 480 three phase
Some are motors
Some are 120v single phase
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Please help list the things to look at to help investigations into why 7 breakers are tripping at the same time.

Some 480 three phase
Some are motors
Some are 120v single phase

Would this happen to be a corner grounded system, then a transformer to supply the 120?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
are they all "standard breakers" (as opposed to gfci, etc)
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Is this a new installation?

If not, what has changed?

This seems like 20 questions... Can't you give us a little more information?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Please help list the things to look at to help investigations into why 7 breakers are tripping at the same time.

Some 480 three phase
Some are motors
Some are 120v single phase

I would suggest you give us as much info as you have available rather than have us try and guess.

There is just no way to even start without more information.

you might start by what you mean by "at the same time". Do you now with certainty they are actually tripping simultaneously? is it possible they are not actually tripping but being turned off?

It seems highly unlikely that seven circuit breakers that are otherwise not connected would just up and trip for no reason. Perhaps you could elaborate a lot more.
 
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hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
Does it only happen when there is a utility loss, and the building has a backup generator that powers only a portion of the service? Breakers are tripping in a non generator powered panel?
 

Natfuelbilll

Senior Member
The facility does have 100% backup power. But this occurs on utility only.

Look at the OP.

What things would you look for?
 

Natfuelbilll

Senior Member
utillity 13.2 kV
3000' to transformer
customer owned 750kVA xfmr to 480/277
brand new installation
distribution built around a MCC
no TVSS installed
cable tray with tray cable distribution
no vfd loads are trupping
tripping at same time
tripping at various different loading conditions
description of loads that are tripping
block heater 480V3P
lighting 277V
heat trace 120V
 

zog

Senior Member
Location
Charlotte, NC
Did anyone do acceptance testing on this new system?
Have you meggered the cables/bus? What were results?
What are measured voltages phase to phase and phase to ground?
 

brian john

Senior Member
Location
Leesburg, VA
1. Does it happen on transfer from generator to utility?
2. Megger all feeders and loads if it is safe to megger loads.
3. Infrared or fall of potential test.
4. Power Monitor loads for during normal operation
5. Check coordination study and breaker settings (If Applicable)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
That is down right weird. How are you generating the 120? Another xfmr? It seems really strange that it would trip downstream of another transformer and upstream at the same time?

Electronic Cbs by any chance?
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
The facility does have 100% backup power. But this occurs on utility only.

Look at the OP.

What things would you look for?

Your original post did not say anything about a generator, but if it was happening on transfer from utility to generator, and you did not have 100% of the loads on generator, I would say one or more generator feed circuits were parralleled somewhere, back feeding the utility until they tripped. But since 100% of the loads are generator powered, this should not be the problem. I had this problem on a blue box store, the lighting maintenance contractor had tied both generator and utility circuits together in the fixtures while changing ballast. They did this to approx. 50 fixtures. Since both circuits were the same phase, but out of different panels, no breakers were tripping until they lost utility, and it backfeed the POCO until the all of the affected breakers tripped due to overload.
 

Haji

Banned
Location
India
I would bet if it is happening on re-transfer to utility it is inrush and is very common.
I think the breakers might be equipped with no volt coil or under voltage relay and short time loss of power during power transfer would trip the breakers.
 
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