1.  Field of the Invention
The present invention relates to protective switching apparatus of the circuit breaker kind, comprising in an insulating case an interruptible current path in which cooperating contacts are disposed, one of which is fixed and the other of which is mobile in response either to the actuation of a member tripping on a fault of electromagnetic and/or thermal origin via a lock, or to the actuation of a voluntary tripping and resetting member such as a lever via a toggle joint mechanism. 
2.  Description of the Prior Art
Circuit breakers of this type are known more especially from the U.S. Pat.  No.  2 352 517.  In these circuit breakers, the mobile contact is disposed at a first end of a contact holder arm whose second end is associated with a retractable support forming the output member of the lock, the contact holder arm being subjected to the action of a quick opening and closure resilient means; the contact holder arm is mounted without a fixed fulcrum point, so as to pivot either by bearing on a surface of the toggle joint mechanism during tripping on a fault, or on a surface of the retractable support of the lock during voluntary manual or automati c tripping. 
The resilient quick opening and closure means is then formed by a member applicable, on the one hand, against the contact holder arm at a point thereof situated between its second end and its bearing point on the toggle joint mechanism, on the other hand, against the case. 
It is more particularly desirable to give to the resilient opening and closure member a simple and compact configuration.