This invention relates generally to a circuit breaker, and, more particularly, to a circuit breaker cassette assembly.
Circuit breakers are one of a variety of overcurrent protective devices used for circuit breaker protection and isolation. The basic function of a circuit breaker is to provide electrical system protection whenever an electrical abnormality occurs in any part of the system. In a rotary contact circuit breaker, current enters the system from a power line. The current passes through a load strap to a stationary contact fixed on the strap and then to a moveable contact. The moveable contact is fixedly attached to an arm, and the arm is mounted to a rotor that in turn is rotatably mounted in a cassette. As long as the fixed contact is in physical contact with the moveable contact, the current passes from the fixed contact to the moveable contact and out of the circuit breaker to downline electrical devices.
In the event of an overcurrent condition (e.g. a short circuit), electro-magnetic forces are generated. These electro-magnetic forces repel the movable contact away from the stationary contact. Because the moveable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and moveable contacts, thus tripping the unit. When the contacts are rapidly opened, as is the case during a trip caused by a short circuit event, an arc is produced. It is common practice to employ an arc chute assembly to extinguish this resultant arc.
Circuit breaker design, and more particularly, cassette design should enable the efficient and proper positioning of the various components, such as the rotor, arc chute assemblies and vent screens, into the cassette. For example, improper installation of a rotor into a cassette can result in the two cassette half pieces not mating correctly together. Also, care must be taken to ensure that an arc chute assembly is correctly positioned into the cassette. This ensures proper rotation of the moveable contact arm as well as the proper spacing between the moveable contact and the plate closest to the moveable contact. Improper installation of a rotor, an arc chute assembly or a vent screen into a cassette half piece will require disassembly and reassembly of the cassette. Such disassembly and reassembly is time consuming and can increase the production cost of the circuit breaker.