Circuit Breaker Frame Size Rating

Paragraph 9 1 4 4 of ul standard 489.

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. And intended for continuous operation at 100 percent of rating shall be marked. Overloads for our purposes can be understood by reference. 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.

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. 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. 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. 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 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. The preferred continuous current ratings of the various frame sizes are listed in ansi c37 16. And cedar rapids iowa respectively. Next up in current quantity this same breaker must be able to open overload level currents.

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.