A circuit breaker cassette comprises a housing having a fixed contact, and a movable contact on a contact arm. The contact arm is positionable in a closed position and an open position, wherein the contact arm is closed when the movable contact is in contact with said fixed contact. A spring biases the movable contact arm towards the closed position A kinetic energy-absorbing stop is positioned to absorb kinetic energy of the contact arm resulting from magnetic repulsive forces forcing the movable contact and the fixed contact apart during a short circuit condition.