A shutter system for a cradle of a rack out circuit breaker comprising: a first rail assembly configured to snap into an interior surface of a side wall of a cradle and a second rail assembly configured to snap into an interior surface of an opposing side wall of the cradle, each of the rail assemblies including: a snap-in lock assembly having: a tab configured to engage an opening in a side wall of the cradle, and a spring guide, at an end of the rail, which is configured to exert a force against a back wall of the cradle to lock the rail along the side wall when the tab is engaged in the opening, and a slider (250,350) movable between a front and back of the cradle along the side wall; a shutter connected to and between the sliders, the shutter being configured: to move with the sliders toward the back of the cradle and into an open position which allows access to buses at the back of the cradle when racking in the circuit breaker, and to move with the sliders away from the back of the cradle and into a closed position which restricts access to the buses at the back of the cradle when racking out the circuit breaker; and a cam actuator, arranged on the first rail assembly or the second rail assembly, configured to cause the shutter to move to the open position when racking in the circuit breaker, and to the closed position when racking out the circuit breaker. a first rail assembly configured to snap into an interior surface of a side wall of a cradle and a second rail assembly configured to snap into an interior surface of an opposing side wall of the cradle, each of the rail assemblies including: a snap-in lock assembly having: a tab configured to engage an opening in a side wall of the cradle, and a spring guide, at an end of the rail, which is configured to exert a force against a back wall of the cradle to lock the rail along the side wall when the tab is engaged in the opening, and a slider (250,350) movable between a front and back of the cradle along the side wall; a shutter connected to and between the sliders, the shutter being configured: to move with the sliders toward the back of the cradle and into an open position which allows access to buses at the back of the cradle when racking in the circuit breaker, and to move with the sliders away from the back of the cradle and into a closed position which restricts access to the buses at the back of the cradle when racking out the circuit breaker; and a cam actuator, arranged on the first rail assembly or the second rail assembly, configured to cause the shutter to move to the open position when racking in the circuit breaker, and to the closed position when racking out the circuit breaker. a tab configured to engage an opening in a side wall of the cradle, and a spring guide, at an end of the rail, which is configured to exert a force against a back wall of the cradle to lock the rail along the side wall when the tab is engaged in the opening, and a slider (250,350) movable between a front and back of the cradle along the side wall; a shutter connected to and between the sliders, the shutter being configured: to move with the sliders toward the back of the cradle and into an open position which allows access to buses at the back of the cradle when racking in the circuit breaker, and to move with the sliders away from the back of the cradle and into a closed position which restricts access to the buses at the back of the cradle when racking out the circuit breaker; and a cam actuator, arranged on the first rail assembly or the second rail assembly, configured to cause the shutter to move to the open position when racking in the circuit breaker, and to the closed position when racking out the circuit breaker. to move with the sliders toward the back of the cradle and into an open position which allows access to buses at the back of the cradle when racking in the circuit breaker, and to move with the sliders away from the back of the cradle and into a closed position which restricts access to the buses at the back of the cradle when racking out the circuit breaker; and a cam actuator, arranged on the first rail assembly or the second rail assembly, configured to cause the shutter to move to the open position when racking in the circuit breaker, and to the closed position when racking out the circuit breaker.