Method and apparatus for protecting alternating current circuits

An apparatus for protecting a circuit from excessive current flow, comprising:

• sense transformer means for sensing the current flow through the circuit;
• pulse shaping means for generating a sense pulse whose width is related to the rate of current flow into the sense transforming means;
• 1st single shot multivibrator means for generating a reference period at the occurrence of each sense pulse;
• 2nd single shot multivibrator means for providing a second pulse each time a sense pulse occurs;
• comparator means for providing an enabling command as long as the sense pulse's width is greater than the reference period and to provide a reset at a fault condition when the sense pulse's width is less than the reference period;
• selectable time delay means for providing a command signal after a fault condition and the occurrence of a selectable number of the second pulses;
• and
• relay means activated by the command signal.