Directional zone select interlock method

A method of operating a circuit breaker in an electrical circuit configured with at least one of a first circuit breaker defining a first zone of protection at a first layer of circuit protection having a first direction of current flow, and at least one second circuit breaker downstream of said at least one first circuit breaker defining a second zone of protection and having a second direction of current flow, and at least one third circuit breaker downstream of said at least one second circuit breaker defining a third zone of protection and having a third direction of current flow, wherein one of said at least one first, second, or third circuit breakers is in short time pick-up, the method comprising the steps of:

• a) identifying a one of said at least one first circuit breaker as a reference circuit breaker;
• c) determining if said identified reference circuit breaker is in reverse current pick-up;
• and if not, determining if a one of said at least one second circuit breaker is in short-time pick-up, indicative of a fault on the circuit;
• and if not;
• d) comparing said third direction of current flow through each of said at least one third circuit breaker with said first direction of current flow through said identified reference circuit breaker;
• e) determining if a one of said at least one third circuit breaker is carrying current in a forward direction with respect to said identified reference circuit breaker;
• and is in short-time pick-up, and if so;
• f) increasing by a predetermined amount the trip time delay of said at least one first and said at least one second circuit breakers upstream of said identified one of at least one third circuit breaker.