The trolley can only be closed when it is in the test/isolation position or working position, and once the circuit breaker is closed, the trolley cannot be moved, thus preventing accidental connection or closing of isolation contacts under load.

When the trolley is in the working position or approximately 10mm away from the test/isolation position, the earthing switch cannot be closed, preventing accidental closing of the earthing switch while live.

When the earthing switch is closed, the trolley cannot move from the test/isolation position to the working position, preventing the closing of circuit breakers when the earthing switch is in the closed position.

Once the chassis trolley enters the cabinet and moves away from the test isolation position, the trolley cannot be withdrawn from the cabinet.