An adjustable mounting assembly for a power circuit breaker includes a frame having a first sidewall disposed opposite a first side of the housing of the power circuit breaker and a second sidewall disposed opposite the second side of the housing. At least one moveable block is disposed between the first and second sidewalls of the frame and the corresponding first and second sides of the housing. An adjustment mechanism, such as a jackscrew coupled to the moveable block, adjusts in order to move the block into engagement with the corresponding sides of the housing. A fastening mechanism, such as a lock screw, secures the moveable block and the frame with respect to the housing. The adjustable mounting assembly securely mounts the frame and the power circuit breaker within a switchgear enclosure in order to resist damage potentially caused by an impact force sustained thereby.