A slide bar interlocking device includes a first group of constrained switch actuators and a second group of unconstrained switch actuators. Only one unconstrained actuator in the first group may be thrown in combination with any switch actuator in the second group and any combination of switch actuators in the second group. A base plate has a fixed position and a movable plate is slideably mounted to the base plate. A plurality of elongate slots is formed in the movable plate and at least one truncate slot is formed in each of the elongate slots. The movable plate has first, second, third, and fourth positions where a switch actuator in the first group is in alignment with a truncate slot so that the aligned switch actuator can be thrown and where all other switch actuators in the first group cannot be thrown.