Circuit breaker with adjustable magnetic trip unit

A circuit breaker structure for responding to abnormal current conditions in an electrical distribution system, comprising:

• a circuit breaker mechamism having separable contacts and having a releasable member movable to an unlatched position from a latched position to effect opening of the contacts;
• a latch lever movable between latched and unlatched positions of the releasable member and being biased in the latched position;
• a trip bar movable to unlatch the latch lever and being biased in the latched position;
• a trip unit comprising a stationary magnetic structure for each conductor of the distribution system and including a coil and core assembly and an armature;
• lever means associated with the stationary magnetic structure for moving the trip bar to the unlatched position;
• the lever means comprising the armature and movable in response to abnormal currents in at least one of the conductors;
• the armature being positioned at a constant distance from said assembly;
• tension means for varying tension on the lever means and comprising adjustable spring means operatively connected to the lever means so that the force required to attract the armature to the assembly is adjustable without varying the distance between the armature and the coil and core assembly;
• the tension means also comprising a manually operable cam and a cam follower;
• the cam follower being operatively connected to the spring means for increasing and decreasing tension on the spring means in response to rotation of the cam;
• and
• indexing means adjacent to and contacting the cam for positively indicating the position of the cam and comprising a retractable member and spaced member-receiving indentations, one of which is disposed in the housing and the member being biased into the indentations, whereby an adjustable magnetic trip is effected by changing the spring force on the armature.