Stored energy trip unit

In a circuit breaker including

• a housing;
• a fixed contact held by said housing;
• a contact movable within said housing, adapted to engage with and disengage from said fixed contact;
• a contact arm coupled to said movable contact;
• means coupled to said contact arm for causing said contact arm to trip when said means is actuated;
• and
• apparatus for actuating said means, the improvement wherein said apparatus comprises
• an electrical circuit including
• a load terminal,
• a bimetal strip having one end fixed to said load terminal and having an opposite end free to bend when thermally excited, and
• a flexible conductive braid having an end fixed to said opposite end and having a second end coupled to said contact arm,
• said load terminal being fixed with respect to said housing;
• an armature latch of ferrous material partially rotatable about a point with respect to said housing;
• having a first end adapted to engage with said opposite end of said bimetal strip,
• having a second end provided with a first retaining means, and
• having an intermediate coupling portion;
• a latch member partially rotatable about a point with respect to said housing,
• having a portion thereof provided with a second retaining means;
• having a coupler adapted to couple with respect to said coupling portion, and
• having an arm for recoupling said coupler subsequent to said coupler becoming uncoupled from said coupling portion;
• and
• a spring coupled between said first retaining means and said second retaining means;
• whereby
• a current overload of a small magnitude through said electrical circuit causes said bimetal strip to be thermally excited and bend, moving and partially rotating said first end of said armature latch, thereby uncoupling said coupling portion from said coupler, whereupon said spring causes said latch member to be rotated, providing an impact momentum to actuate said means coupled to said contact arm, thereby tripping said contact arm, opening said contacts, and
• a current overload of a high magnitude through said electrical circuit sets up a sufficiently strong magnetic field to thereby rapidly attract and partially rotate said ferrous armature latch, thereby uncoupling said coupling portion from said coupler, whereupon said spring causes said latch member to be rotated, providing an impetus to actuate said means coupled to said contact arm, thereby tripping said contact arm, opening said contacts.

A trip unit for a circuit breaker comprising

• a carrier member having two separate, spaced-apart axes;
• a first member adapted to pivot about one of said axes, said first member having a latching portion distant from said one axis;
• a second member adapted to pivot about the other of said axes, said second member having a latching portion distant from said other axis;
• and
• a spring connecting said first member to said second member so that said first member and said second member are latched together at said latching portions thereby forming a triangular geometry with said members, whereby
• rotation of said first member about said one axis in an unlatching direction causes said first member to unlatch from said second member, and
• rotation of said second member about said other axis in a latching direction causes said second member to latch with said first member.