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Circuit Breaker Ratings

June 2nd, 2009 2 comments

Many circuit breakers have labels displaying the breaker’s amperage rating and the interrupting current rating based on different voltage levels.  Circuit breakers have an interrupting rating of so many thousands of amps at so many volts.  The higher you go with voltage, the lower you should try to interrupt with the breaker.  Another way, the available fault current should not exceed the interrupting rating of any of the circuit breakers on that circuit.  Excluding some problem with an importer of inferior products that could not pass acceptance tests, it is doubtful that a circuit breaker manufacturer would produce a circuit breaker that could be used at 208 Volts and no higher.  So circuit breaker manufacturers make a given breaker to handle multiple voltages.  The first or highest interrupting rating applies when the system voltage is 240AC, 250 DC or 208 AC.  The breaker could also have an interrupting rating for 480 Volts and an even lower interrupting rating for 600 Volts.  You can not pick and choose the ratings to try to get more from a circuit breaker.  Your system voltage dictates which interrupting rating applies.