The X/R method of applying power circuit breakers

A NEW BASIS for rating power circuit breakers was proposed at the January 1954 AIEE Winter General Meeting by the Working Group on Methods of Rating Power Circuit Breakers. This group proposed that the making, latching, and interrupting current ratings of circuit breakers be combined into one rating, rated short-circuit current, having specified characteristics which a breaker shall be able to close, carry, and interrupt with any permissible delay in tripping on a predominantly resistive or inductive circuit. To compare these specified characteristics with the decrement rates for asymmetrical fault currents on high-voltage systems, a so-called X/R method has been developed and is intended for use as the basis for a simplified application procedure for power circuit breakers rated on the proposed new basis.