This publication represents standard practices in the United States relating to alternating-current power circuit breakers. It contains data secured from many sources notably the established standards of the American Institute of Electrical Engineers and the National Electrical Manufacturers Association. It also includes data prepared by the Association of Edison Illuminating Companies. This publication combines, in one reference work, information relating to the terms and conditions upon which the rating and behavior of alternating-current power circuit breakers are based. The publication is divided into six parts. The main part consists of a definite Standard, C37.4-1945, for alternating-current power circuit breakers, which covers definitions and ratings of apparatus coming within the scope of this work. The remainder consists of supplementary standards, one of which, C37.9-1945, covers the procedure for testing circuit breakers. The Schedule of Preferred Ratings for Indoor and Outdoor Circuit Breakers, C37.6-1945, is included.

These standards apply to all indoor and outdoor types of alternating-current power circuit breakers rated in excess of 600 volts