The automated circuit breaker diagnostic system described in this paper is an extension of the widely used portable circuit breaker testing device concept. The testing devices can be connected to the circuit breaker's control circuit to record analog and digital signals. The automated system consists of a signal processing module and an expert system module. The two modules process the voltage and current signals recorded by the testing device, diagnose and report any abnormalities that are discovered. The paper describes the system requirements, the implementation of the two system modules, and provides an example that demonstrates the entire process. Real data recorded in a substation has been used to test the system.