Abstract: A circuit breaker actuating mechanism has a magnetic frame and a load coil, with a magnetic pole piece which is aligned with the axis of the coil. An elongate L-shaped armature pivots on the magnetic frame and has a head which moves transversely relative to the axis of the coil towards the pole piece. The pole piece is typically circular in section, and the head of the armature has a circular recess which matches the shape of the pole piece. The head of the armature has a pair of projections which extend relatively close to the pole piece when the armature is in a retracted position, increasing the initial attractive force between the pole piece and the armature. The mechanism is relatively simple and economical to manufacture, and offers an improved pull-in force.

Abstract: A circuit breaker includes a tripping device in which a magnetic core is contained in a vessel of viscous fluid in a magnetic frame. An armature is disposed adjacent the core and is connected to a toggle mechanism. Under conditions of moderate overloads, the armature and the core ineract and the tripping device provides a time delay before it operates. Under severe fault conditions the armature is activated directly and the effect of the core is of less significance. The core or the armature are tapered, to provide a desired balance between the delayed and instantaneous operating characteristics.