circuit breaker magnetic trip
- Thread starter electrics
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kingpb
Senior Member
- Location
- SE USA as far as you can go
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- Engineer, Registered
Trip rating and withstand rating are two different things.
For instance the breaker may be capable of withstanding 14,000 amps, but it may be set to trip at 5000A. So as long as the fault current is limited to 14,000 A or less, then it will not be damaged. However, if you set it at 5000 A to trip instantaneously (magnetic) and there is only 4000A of fault current, the breaker will not trip for the fault.
Very important to do fault current calculations and protective device coordination.
For instance the breaker may be capable of withstanding 14,000 amps, but it may be set to trip at 5000A. So as long as the fault current is limited to 14,000 A or less, then it will not be damaged. However, if you set it at 5000 A to trip instantaneously (magnetic) and there is only 4000A of fault current, the breaker will not trip for the fault.
Very important to do fault current calculations and protective device coordination.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Magnetic trip settings are intended to protect the LOAD.
Interrupt Ratings (AIC) are what the breaker can withstand without creating shrapnel.
Most modern breakers have a high limit of 10X the frame rating as a magnetic over ride trip value, meaning that regardless of the setting of the magnetic trips, the breaker will try to open at 10X current. At that point if the available fault current is lower than the AIC rating of the breaker, it should interrupt the fault and be capable of being reset at least once. But if the available fault current is higher than the AIC rating of the breaker, it may explode in it's attempt to interrupt the fault current by the magnetic forces the current created.
But if that is the case, someone picked the wrong breaker!
Interrupt Ratings (AIC) are what the breaker can withstand without creating shrapnel.
Most modern breakers have a high limit of 10X the frame rating as a magnetic over ride trip value, meaning that regardless of the setting of the magnetic trips, the breaker will try to open at 10X current. At that point if the available fault current is lower than the AIC rating of the breaker, it should interrupt the fault and be capable of being reset at least once. But if the available fault current is higher than the AIC rating of the breaker, it may explode in it's attempt to interrupt the fault current by the magnetic forces the current created.
But if that is the case, someone picked the wrong breaker!
brian john
Senior Member
- Location
- Leesburg, VA
If you have a 100 and CB with adjustable instantaneous, typically they are 4-10 times or 400-1000 (though these are plus or minus these settings), some may be 6-10, 4-12 and with larger draw-out circuit breakers some may be 2-14. Depends on manufacture and job requirements.
If you have an CB with instantaneous set at 8 and your inrush current is 10X, then the CB will (SHOULD) trip.
If you have an CB with instantaneous set at 8 and your inrush current is 10X, then the CB will (SHOULD) trip.
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