CIRCUIT BREAKER THERMAL MAGNETIC TRIP UNIT

A thermal-magnetic trip unit (22), suitable for use in a circuit breaker (9), for eliminating the requirement for latching surfaces while still providing the additional force and motion required to trip the breaker (9) during a short circuit or an overcurrent trip event. The trip unit (22) comprises a link (34) that is biased based on the position of a trip bar (30). A spring (42) biases the link (34) in a first direction when the trip unit (22) is in a reset condition and biases the link (34) in a second direction when the trip bar (30) is rotated about a pivot point (32). A trip unit (22) further including an improved indication-of-trip system comprising a two-piece trip bar mechanism and flag system is described to discriminate between overcurrent and short circuit faults. In this embodiment of teh invention, visual confirmation of the cause of the trip is provided. The case (11) of the circuit breaker (9) in this embodiment of the invention includes a window 8124) disposed therein in a location conducive to a user viewing an identification flag (132, 134) thus enabling the rapid determination of the type of trip which has occurred. To identify a trip caused by an overcurrent condition, a first flag (132) is employed. To identify a trip caused by a short circuit condition, a second flag (134) is employed. If an overcurrent event occurs then the first slide (38) of the two piece trip bar mechanism moves to expose the first flag (132). If a short circuit event occurs, only the second slide (104) of the two-piece trip bar system moves to expose the second flag (134).