Power-circuit-breaker ratings

CIRCUIT breaker application is being simplified. A subcommittee of the protective devices committee of the AIEE has studied methods of calculating short circuit currents and has prepared a report which presents a simplified procedure based on standardized contact parting times and typical current decrements.¹ To facilitate the use of this method, circuit breakers should have ratings which conform to the short circuit characteristics assumed in the calculations. At the present time, while the industry is preparing a revised list of short-time current ratings for circuit breakers, an opportunity exists to correlate the short circuit ratings so that a breaker selected for adequate interrupting current by the new method automatically has ratings adequate for the other short circuit currents. The rating of a power circuit breaker as given by AIEE Standard 19–200 includes the following items: