Abstract: An apparatus selectively connects a normal power line and an emergency power line to a load, and includes two interlocked switching mechanisms, each having individual interlocks, for selectively connecting the power lines to the load, and an interlock mechanism for interlocking the switching mechanisms in order that only one of the power lines at a time is connected to the load. The switching mechanisms may each have two drawout cassettes including associated switching devices for switching the power lines to the load and, also, including an isolated position for isolation of the associated switching device from at least one of the switched power lines and the load. Each switching device may be a circuit breaker having a trip unit for sensing current flowing from a power line to the load and tripping the circuit breaker. The interlock mechanisms may include keylock mechanisms which selectively disable closing of the switching devices.

Abstract: An uninterruptible power source having a static transfer switch which switches rapidly between a commercial power source and an alternate power source is removed from service by a maintenance bypass switch having a first switch in series with the uninterruptible power source and a second switch which shunts the uninterruptible power source and the first switch. The first and second switches are circuit breakers having handles which toggle between open and closed positions. The maintenance bypass switch includes an operator which operates the two circuit breakers in opposition with a closed transition so that one switch is always closed. An interlock prevents operation of the maintenance bypass switch when the alternate power source of the uninterruptible power supply is selected by the static transfer switch.