In a utility power distribution system having at least one primary electric power
source and at least one secondary electric power source, each of said primary and
secondary sources being connected to the distribution system through respective
controllable circuit breakers, the improvement comprising communication signal
generating apparatus arranged for introducing a communication signal into the power
distribution system from the connection of the primary power source, communication
signal receiving apparatus arranged for receiving the communication signal via
the power distribution system at the secondary power source, and apparatus responsive
to the interruption of receipt of the communication signal at the receiving apparatus
for operating the circuit breakers at the secondary power source for disconnecting
the secondary power source from the power distribution system.
