Abstract: An interlock for first and second circuit breaker switch mechanisms which respectively have first and second operating handles thereon oriented such that the direction of operation is transverse in relation to the other. The interlock includes an interlock mechanism disposed between the first and second switch mechanisms and includes a support, a first interlock member interconnected with the first operating handle, and a second interlock member interconnected with the second operating handle. The first and second interlock members are mounted to the support for movement relative to each other along with the respective first and second operating handles. The interlock members include interference structure to prevent the second switch mechanism from being in an ON position when the first switch mechanism is in its ON position and likewise to prevent the first switch member from being in an ON position when the second switch member is in its ON position.