Variable thermal and magnetic structure for a circuitbreaker trip unit

A thermal and magnetic trip unit for a circuit breaker, the circuit breaker including a principal conductive current path through which load current flows, the circuit breaker further including first and second contacts which are closed to allow the load current to flow through the principal conductive current path and which are opened to stop current flow through the principal conductive current path, wherein the breaker includes a trip bar that is engaged to open the contacts of the circuit breaker on the occurrence of a trip condition, the trip unit comprising:

• a bimetallic element configured adjacent to the trip bar and having a conductive path which is coupled to conduct at least a portion of the load current when the contacts of the circuit breaker are closed, the conductive path of the bimetallic element having an ohmic resistance such that, during an overcurrent condition, the current conducted by the conductive path generates heat within the bimetallic element and the bimetallic element is responsive to heat to bend and engage the trip bar;
• a generally "U" shaped conductive heating element having first and second legs which define a resistive current path, wherein the load current flows through the heating element from the first leg to the second leg;
• a configurable insulator adapted to be inserted between the heating element and the bimetallic element to insulate the heating element from the bimetallic element
• a configurable connecting bus element which is adapted to electrically connect the second leg of the heating element to the bimetallic element,
• whereby when the insulator and the connecting bus element are inserted, the resistive current path of the heating element is in series with the conductive path of the bimetallic element and the combination of the heating element, the connecting bus element and the bimetallic element form a coil, and whereby, when the insulator is removed, the resistive current path of the heating element is in parallel with the conductive path of the bimetallic element.

A thermal and magnetic trip unit for a circuit breaker, the circuit breaker including a principal conductive current path through which load current flows, the circuit breaker further including first and second contacts which are closed to allow the load current to flow through the principal conductive current path and which are opened to stop current flow through the principal conductive current path, wherein the breaker includes a trip bar that is engaged to open the contacts of the circuit breaker on the occurrence of a trip condition, the trip unit comprising:

• a bimetallic element configured adjacent to the trip bar and having a conductive path which is coupled to conduct at least a portion of the load current when the contacts of the circuit breaker are closed, the conductive path of the bimetallic element having an ohmic resistance such that, during an overcurrent condition, the current conducted by the conductive path generates heat within the bimetallic element and the bimetallic element is responsive to heat to bend and engage the trip bar;
• a generally "U" shaped first conductive heating element having first and second legs which define a resistive current path, wherein the load current flows through the first heating element from the first leg to the second leg;
• a configurable first insulator adapted to be inserted between the heating element and the bimetallic element to insulate the heating element from the bimetallic element
• a configurable first connecting bus element which is adapted to electrically connect the second leg of the heating element to the bimetallic element,
• a generally "U" shaped configurable second conductive heating element having first and second legs which define a resistive current path, wherein the load current flows through the second heating element from the first leg to the second leg;
• a configurable second insulator adapted to be inserted between the second heating element and the first heating element to electrically insulate the second heating element from the first heating element
• a configurable second connecting bus element which is adapted to electrically connect the second leg of the second heating element to the first heating element, whereby when the second insulator and the second connecting bus element are inserted, the resistive current path of the second heating element is in series with the conductive path of the first heating element and the conductive path of the bimetallic element and the combination of the first and second heating elements, the first and second connecting bus elements and the bimetallic element form a coil, and whereby, when the first and second insulators are removed, the resistive current paths of the first and second heating elements are in parallel with the conductive path of the bimetallic element;
• a magnetically permeable yoke having a generally "U" shaped cross section which surrounds one leg of the combined first and second heating elements and bimetallic element on three sides such that the yoke concentrates a magnetic field generated by the combined first and second heating elements and the bimetallic element;
• a ferromagnetic armature, separated from the yoke by a gap such that the magnetic field concentrated by the yoke produces a magnetic force which causes the armature to engage the yoke when the magnetic force is greater than a predetermined threshold force, the armature being positioned, with respect to the trip bar such that, when the armature engages the yoke, the armature also engages the trip bar.