Abstract: A switch has contacts constructed so that an electro-dynamic force is created by the current flowing through the switch which tends to maintain the switch in a closed state. This force counteracts other electro-dynamic forces which tend to open the switch. The contact design is particularly adapted from use in a single pole-double throw switch having a contact arm that is movable between two fixed contacts. The electro-dynamic force compensation exists between the contact arm and whichever one of the fixed contacts the contact arm is against. The fixed contacts also include arc runners so that any arc that develops as the contacts separate eliminates electro-dynamic force which tends to maintain the switch in a closed state.

Abstract: An automatic electric load transfer switch incorporates an over-the-center spring mechanism to operate switch contacts. The spring mechanism has a first position at which the electric load is connected to one electricity source and a second position at which the load is connected to another electricity source. The spring mechanism is driven by a solenoid activated cam shaft. An apparatus is provided for halting the movement of the spring mechanism at a position intermediate the first and second positions at which the load is not connected to either electricity source. The halting apparatus is releasable so that the spring mechanism can continue its movement between the first and second positions.

Abstract: One or more sets of auxiliary contacts are contained within a cartridge which mounts to the side of an electromagnetic contactor. The cartridge snaps into position and is firmly supported at each of its ends. A cam member slidably mounts to the cartridge and couples to the contactor actuator. It includes a sloping cam surface which engages a cam follower pivotally mounted within the cartridge and translates the sliding motion of the contactor actuator into a pivotal motion which operates the auxiliary contacts.