Abstract: A mechanism for a circuit breaker includes a support lever insulated from a contact arm and a trip lever supported by a plate fitted with limited swivelling on a pivot. A mechanical link arranged between a toggle-joint and the contact arm includes a latching stop fixed on the plate. The stop is formed by a notch cooperating with a step of the trip lever to push the end of a toggle rod back to a retracted unlatched positon, as soon as the trip lever is actuated to the tripped position. The support lever is equipped with a locking arm having a sloping part cooperating with a pawl of the handle to form a high-speed contact closing device.