This standard pertains to the requirements for direct-acting current and voltage protective functions of the following that are integral with low-voltage ac and dc power circuit breakers covered by IEEE Std C37.13 and IEEE Std C37.14: a) Direct-acting overcurrent electromechanical trip devices b) Direct-acting overcurrent electronic trip systems c) Reverse-current trip systems for dc circuit breakers d) Undervoltage trip devices This standard describes the requirements for available settings and time delay characteristics for preferred protective functions as well as their operational and calibration requirements. The functional requirements for the overall circuit breaker, including test requirements (whether design, production, or conformance) are specified in the latest versions of IEEE Std C37.13, IEEE Std C37.14, and ANSI C37.50. This standard does not restrict the inclusion of additional internal or external functionality in the trip system or device.