What is the problem?

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anbm

Senior Member
Switchboard 'MA' (4,000A, 480Y/277V) has a 800A LSIG breaker, this breaker feeds ATS-1.

ATS-1 feeds panel 'B' (800A MLO, 480Y/277V).

Panel 'B' has a 300A branch breaker which feeds motor control center 'C'.

The elevator was fed out of motor control center 'C' via a fused disconnect switch and starter (fuse size couldn't be identified, but disconnect size was 30A).

When the elevator starts and fails, 800A CB in switchboard 'MA' was tripped but not 300A CB in panel 'B' or neither fused disconnect that feeds the elevator.

Do you think this is a coordination study problem or something else? I couldn't understand...
 

charlie b

Moderator
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Location
Lockport, IL
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Retired Electrical Engineer
Do you think this is a coordination study problem. . . ?
Yes. When a short circuit happens, the high fault current travels through every breaker or fuse from the fault point back to the main service. All such devices are going to go into their "I gotta trip" mode. One of them will trip before the others. Why would you expect any one in particular to be the one that wins the race? The instantaneous trip of an 800 amp breaker can act as fast as that of a 30 amp breaker. If you want to prevent this from happening, you need a coordination study, and you need to reset the breakers based on the results of the study.

 

zog

Senior Member
Location
Charlotte, NC
Switchboard 'MA' (4,000A, 480Y/277V) has a 800A LSIG breaker, this breaker feeds ATS-1.

ATS-1 feeds panel 'B' (800A MLO, 480Y/277V).

Panel 'B' has a 300A branch breaker which feeds motor control center 'C'.

The elevator was fed out of motor control center 'C' via a fused disconnect switch and starter (fuse size couldn't be identified, but disconnect size was 30A).

When the elevator starts and fails, 800A CB in switchboard 'MA' was tripped but not 300A CB in panel 'B' or neither fused disconnect that feeds the elevator.

Do you think this is a coordination study problem or something else? I couldn't understand...

Does the 300A CB have a ground fault function?
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Well there you go, if the elevator has a ground fault the first protective device that will respond is your 800A breaker.

Good call, first thing to check.

If the fault is not GF, then most likely the instantaneous on the 800A is tripping. As cb pointed out you have a coordination issue.

I would suspect that the factory settings on the breakers were not updated with the actual settings needed for coordination.
 

zog

Senior Member
Location
Charlotte, NC
Switchboard 'MA' (4,000A, 480Y/277V) has a 800A LSIG breaker, this breaker feeds ATS-1.

800A CB in switchboard 'MA' was tripped but not 300A CB in panel 'B' or neither fused disconnect that feeds the elevator.

.

What function is the 800A breaker tripping on? Your trip unit should tell you this and that is a big clue.
 

anbm

Senior Member
Good call, first thing to check.

If the fault is not GF, then most likely the instantaneous on the 800A is tripping. As cb pointed out you have a coordination issue.

I would suspect that the factory settings on the breakers were not updated with the actual settings needed for coordination.

The fuse size for elevator can't larger than 30A, so I assume elevator inrush can't be larger than 800A?
 

anbm

Senior Member
Depends on the model trip unit you have. It is possible there are no indicators, some older (>30 years) ones don't, some it is an option when purchasing, most modern ones have them.

Kill me...if I understand what you wrote (-:
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Do you have a TCC for the switchgear main, feeder, and elevator protection? I am guessing no, but that is what is needed. Wouldn't take but a few minutes to generate once the correct info is in hand. Would need it for GF and phase protection plots.
 
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