Patent ID: 8514531
Filing Date: 2013-08-20
Classification: H02H

Abstract:
1. A trip unit comprising: a current sensor structured to sense a value of current flowing through a conductor; a circuit structured to receive first frequency pulses having a number of first frequencies from said conductor; a transmitter structured to transmit second frequency pulses having a second frequency to said conductor, said second frequency being different than said number of first frequencies; and a processor comprising a routine structured to input the sensed value of current from said current sensor, determine if the sensed value of current exceeds a predetermined value and responsively cause said transmitter to transmit the second frequency pulses having the second frequency to said conductor, monitor within a predetermined time after determining that the sensed value of current exceeds the predetermined value if a number of the first frequency pulses having the number of first frequencies is received by the circuit from said conductor, and responsively delay outputting a trip signal, and, otherwise, immediately output the trip signal.