American and European circuit breaker rating

THE DIFFICULTY in comparing the ratings of European and American power circuit breakers results from differences in the methods of stating the interrupting rating. The rms value of a short-circuit current usually varies with time. Its maximum value occurs at the initiation of an asymmetrical short circuit and is the value of current which must be closed or carried by the breaker. The currents to be interrupted include those which are initially asymmetrical and which at contact parting still may have appreciable asymmetry. Consequently the ratings must state the ability of the breakers to close or carry and to interrupt both symmetrical and asymmetrical currents.