A locking device for an electrical switchboard, comprising: - a housing designed to be mounted on an electrical panel between a first switching device and a second switching device, each of the switching devices comprising a control lever (24, 28) that can be moved between a low position corresponding to an open state and a high position corresponding to a closed state; - a locking component rotatable about an axis of rotation substantially perpendicular to a front face of the housing, the locking member comprising a blocking edge, a first contact edge and a second contact edge, the blocking edge lying between the first contact edge and the second contact edge, the locking member being reversibly movable between: - a first locking position, in which the locking member locks the control lever of the first switchgear in the open position, by cooperation of the locking edge with the control lever of the first switchgear, the second contact edge being aligned with the direction of movement of the control lever of the second switchgear to allow movement of the control lever of the second switchgear towards its closed position, and - a second locking position, in which the locking member locks the control lever of the second switchgear in the open position, by cooperation of the locking edge with the control lever of the second switchgear, the first contact edge being aligned with the direction of movement of the control lever of the first switchgear to allow movement of the control lever of the first switchgear towards its closed position, characterised in that: - the locking member is also movable into a third locking position intermediate between the first locking position and the second locking position, in which the first control lever and the second control lever of the switching devices are both locked in the open position by the locking member and held in the open position. - a housing designed to be mounted on an electrical panel between a first switching device and a second switching device, each of the switching devices comprising a control lever (24, 28) that can be moved between a low position corresponding to an open state and a high position corresponding to a closed state; - a locking component rotatable about an axis of rotation substantially perpendicular to a front face of the housing, the locking member comprising a blocking edge, a first contact edge and a second contact edge, the blocking edge lying between the first contact edge and the second contact edge, the locking member being reversibly movable between: - a first locking position, in which the locking member locks the control lever of the first switchgear in the open position, by cooperation of the locking edge with the control lever of the first switchgear, the second contact edge being aligned with the direction of movement of the control lever of the second switchgear to allow movement of the control lever of the second switchgear towards its closed position, and - a second locking position, in which the locking member locks the control lever of the second switchgear in the open position, by cooperation of the locking edge with the control lever of the second switchgear, the first contact edge being aligned with the direction of movement of the control lever of the first switchgear to allow movement of the control lever of the first switchgear towards its closed position, - a first locking position, in which the locking member locks the control lever of the first switchgear in the open position, by cooperation of the locking edge with the control lever of the first switchgear, the second contact edge being aligned with the direction of movement of the control lever of the second switchgear to allow movement of the control lever of the second switchgear towards its closed position, and - a second locking position, in which the locking member locks the control lever of the second switchgear in the open position, by cooperation of the locking edge with the control lever of the second switchgear, the first contact edge being aligned with the direction of movement of the control lever of the first switchgear to allow movement of the control lever of the first switchgear towards its closed position, characterised in that: - the locking member is also movable into a third locking position intermediate between the first locking position and the second locking position, in which the first control lever and the second control lever of the switching devices are both locked in the open position by the locking member and held in the open position. - the locking member is also movable into a third locking position intermediate between the first locking position and the second locking position, in which the first control lever and the second control lever of the switching devices are both locked in the open position by the locking member and held in the open position.