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.

Rounded up to 50a. Next up in current quantity this same breaker must be able to open overload level currents. Paragraph 9 1 4 4 of ul standard 489. 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. 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. 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. And cedar rapids iowa respectively.

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. 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. And intended for continuous operation at 100 percent of rating shall be marked.

Overloads for our purposes can be understood by reference.