A power line communication system. The system includes at least one transmitter for generating and transmitting signals over a power line and at least one receiver for the receipt of signals transmitted over the power line. The transmitter and receiver(s) devices include a storing mechanism containing the address of the device and a programming port for electrical connection to a mating connector of a programmer. The programmer also includes a selector for selection of a desired address such that the address of the addressable device may be changed by the programmer. The transmitter also includes a timing mechanism for automatically retransmitting signals over the power line and the receiver includes a time measuring mechanism for ascertaining whether a signal has been received within a predetermined time period and a mechanism for setting the receiver in a default state should no signals be received within that time period. The invention also includes a test transmitter capable of generating and transmitting selected signals over the power line for testing the receivers connected to the power line, and a test receiver for monitoring and displaying both the data and the strength of signals transmitted over the power line.