A power unit in a motor control center comprises an extendable/retractable carriage assembly and a power connection configurable to prevent an operator from accidentally energizing the power unit. A carriage follower coupled to the carriage assembly and in contact with a rotatable linkage may rotate the rotatable linkage to position an operator handle blocking surface. In a blocking position, the blocking surface prevents rotation of an operator handle to an operator handle position associated with energizing the power unit and in a nonblocking position, the blocking surface allows rotation of the operator handle to the operator handle position associated with energizing the power unit.