Electronic trip unit for circuit breakers

An electronic trip unit for a circuit breaker is disclosed. The electronic trip unit has a processing circuit, a real time clock chip, and a power source for powering the real time clock chip in the absence of current in the circuit breaker. The processing circuit is responsive to input signals representative of a current in the circuit breaker, and productive of a trip signal for tripping the circuit breaker. The real time clock chip is in signal communication with the processing circuit. In response to an off event at the circuit breaker following a current flow condition thereat, the real time clock chip is configured to generate time information for use by the processing circuit, which is configured to apply the time information to calculate a cooling effect arising from the circuit breaker being off, thereby providing for thermal memory.