A system for checking synchronization of AC voltage sources before closing a power circuit breaker is provided comprising two power circuit breakers connected by a power transmission line, such as by using remote voltage via fiber channel. Each circuit breaker is respectively connected to a bus and a protective relay. The circuit also comprises voltage transformers between the bus and the protective relay. The protective relays monitor the voltages on the bus side of the circuit breakers and current flowing through the circuit breakers in order to detect short circuits on the line. A bidirectional communications link is further provided for connecting protective relays together.