Circuit Breaker Frame Size Rating

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

Circuit breaker frame size rating.

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. 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. 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. Although 100 rated devices typically are not available in sizes this small the permitted rating would still be 50a 16a 30a 46a.

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. Overloads for our purposes can be understood by reference. 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 preferred continuous current ratings of the various frame sizes are listed in ansi c37 16.

Next up in current quantity this same breaker must be able to open overload level currents. 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. 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. 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.

Rounded up to 50a.