a method of manufacturing a circuit breaker comprises the steps of preassembling the movable parts of the circuit breaker between a pair of frame members and providing a housing that is configured for supporting the unitary breaker assembly without attachments . other circuit breaker components , attached to the unitary breaker assembly , are also supported in the housing without attachments . a cover is secured to the housing to complete the circuit breaker . another version of the invention preassembles the movable parts of the circuit breaker and the stationary contact mechanism and trip coil , with the line and load terminals attached , between a pair of supporting frame members to form an operable circuit breaker module . the module is in turn supported in a housing without attachments . the circuit breaker module may be tested and adjusted prior to final assembly .