Power line communication over ground and neutral conductors of plural residential branch circuits

Claim 1

A power line communication system for signalling over a low voltage AC power distribution system for distributing electrical power at an AC power frequency throughout a building, wherein the power distribution system includes a load center and a plurality of branch circuits, the load center having at least one main busbar to which a main of a service entry feed is connected and a neutral bus to which a neutral cable of the service entry feed is connected, the neutral bus being solidly clamped to ground potential, each branch circuit having a line conductor electrically connected with the main busbar and a neutral conductor terminated in electrical connection with the neutral bus, said communication system comprising, in combination: A. a ground bus included in the load center; B. a tie conductor electrically connecting said ground and neutral buses in common; C. a signal communication link consisting of at least one of the branch circuits, said one branch circuit including, in addition to a line conductor and a neutral conductor, a ground conductor terminated in electrical connection with said ground bus and otherwise electrically isolated from the neutral conductor thereof downstream from the load center; D. a transmitter for transmitting voltage signals of a frequency greater than the power frequency and coupled onto said communication link; E. a receiver tuned to said voltage signals and coupled onto said communication link; and F. inductive means associated with said tie conductor to introduce an impedance between said ground and neutral buses at the signal frequency such as to accomodate the propagation of voltage signals along said one branch circuit between said transmitter and receiver, said voltage signals being precluded from propagating onto the neutral cable of the service entry feed by virtue of the neutral bus being clamped to ground potential at the voltage signal frequency.