In addition to the complexities in determining the possible
end of life for a MCCB, electrical safe workplace standards
such as the National Fire Protection Association’s NFPA-70E
[4] place a new emphasis on a circuit breaker interrupting a
fault as designed and also clearing the fault in a repeatable
fashion, within a prescribed clearing time. The IEEE
companion document Standard IEEE1584 [5] includes
methods to calculate downstream electrical arc flash energy
based on breaker time-current curves published by the
manufacturers of these products. If a MCCB has been in
service for a long period of time and has not been properly
maintained, or if the device has repeatedly interrupted high
level faults near the device’s interrupting rating in the past, it ‘s
difficult to know with some measure of confidence that the
breaker is capable of interrupting a future fault.