Archive for June, 2009

Circuit Breakers Are Not Always Trouble Free

June 10th, 2009 Comments off

Circuit breakers are unlike fuses as they are designed to open and close all three phases at once.  This is a definite plus as the power can be restored after the system problem has been corrected.  But even circuit breakers have their warts.  They can be slower acting than fuses and sometimes one or more of the poles can fail in the ‘open’ or ‘closed’ position.  If they have not been maintained for years, they could act even slower than usual or worse they may not react to a faulted condition at all.  This could result in the same kind of overheating condition you could experience with two out of three fuses providing some power to a machine.  You know where one fuse blows or ‘goes’ prematurely and the other two hold and then you slowly cook the machine’s motor to death.  Why? Because the power from the remaining two phases, if it will spin the motor at all, will not be able to turn the fan blade on the motor shaft fast enough to provide adequate cooling. 


Best remedy to keep circuit breakers fit is to routinely open and close them to keep the mechanisms moving a few times, maybe ten or so times, so all of the moving parts break through any accumulated buildup of grease and grime.  Remember just because a machine is not moving does not mean the power is turned off. 

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.