Circuit Breaker Frame Size Rating

In the range of molded case circuit breakers conforming with the ul 489 and csa c22 2 standard abb proposes an entire range which covers current ratings between 15 a and 2500 a and interrupting ratings at 480 v ac which can reach 150 ka.

Circuit breaker frame size rating.

60 amp low voltage molded case thermal magnetic breaker must be able to open or close at 48 amps 80 of its rating or less. Overloads for our purposes can be understood by reference. The general rule of thumb is that circuit breaker size should be 125 of the ampacity of cable and wire or the circuit which has to be protected by the cb. Frame size rating a circuit breaker which can be fitted with overcurrent tripping units of different current level setting ranges is assigned a rating which corresponds to the highest current level setting tripping unit that can be fitted.

Interrupting ratings like 10k 22 5k and 65k rms ensure the breaker has an interrupting rating sufficient for the maximum possible fault current available on the line side terminals of the equipment. The rated continuous current of a circuit breaker equipped with direct acting trip devices or fuses of a lower rating than the frame size of the circuit breaker is determined by the rating of those devices. Rounded up to 50a. And cedar rapids iowa respectively.

The preferred continuous current ratings of the various frame sizes are listed in ansi c37 16. To determine the appropriate size of circuit breaker for single phase supply it depends on multiple factors like type of load cable material and environment temperature etc. And intended for continuous operation at 100 percent of rating shall be marked. A circuit breaker having a frame size of 250 a or greater or a multi pole type of any ampere rating rated over 250 v.

Jim pauley is manager industry standards and sandi young is circuit breaker product specialist with square d co lexington ky.