A mechanical interlock assembly for a disconnector and an earthing switch, comprising: a main interlock disc configured to actuate a movable contact of a disconnector, and at least one earthing switch interlock disc (173, 173') configured to actuate a respective movable contact of at least one earthing switch (12, 13) respectively; wherein the main interlock disc is provided with at least one first groove, and each of the at least one earthing switch interlock disc (173, 173') is provided with a third groove, and between the main interlock disc and each of the earthing switch interlock disc (173, 173') is provided with a movable interlock pin respectively; wherein the at least one first groove is aligned with the respective interlock pin (174, 174') when the movable contact of the disconnector is in an open position, such that each of the earthing switch interlock discs (173, 173') is rotatable to push the respective interlock pin (174, 174') to engage with the at least one first groove respectively to stop the main interlock disc from rotating so as to lock the movable contact of the disconnector in the open position while the movable contact of the at least one earthing switch (12, 13) is moved to a closed position; and the third groove on each of the at least one earthing switch interlock disc (173, 173') is aligned with the respective interlock pin (174, 174') when the movable contact of each of the earthing switch (12, 13) is in an open position, such that the main interlock disc is rotatable to push the respective interlock pin (174, 174') to engage with the third groove on each of the at least one earthing switch interlock disc (173, 173') respectively to stop each of the at least one earthing switch interlock disc (173, 173') from rotating so as to lock the movable contact of each earthing switch (12, 13) in the open position while the movable contact of the disconnector is moved to a closed position. a main interlock disc configured to actuate a movable contact of a disconnector, and at least one earthing switch interlock disc (173, 173') configured to actuate a respective movable contact of at least one earthing switch (12, 13) respectively; wherein the main interlock disc is provided with at least one first groove, and each of the at least one earthing switch interlock disc (173, 173') is provided with a third groove, and between the main interlock disc and each of the earthing switch interlock disc (173, 173') is provided with a movable interlock pin respectively; wherein the at least one first groove is aligned with the respective interlock pin (174, 174') when the movable contact of the disconnector is in an open position, such that each of the earthing switch interlock discs (173, 173') is rotatable to push the respective interlock pin (174, 174') to engage with the at least one first groove respectively to stop the main interlock disc from rotating so as to lock the movable contact of the disconnector in the open position while the movable contact of the at least one earthing switch (12, 13) is moved to a closed position; and the third groove on each of the at least one earthing switch interlock disc (173, 173') is aligned with the respective interlock pin (174, 174') when the movable contact of each of the earthing switch (12, 13) is in an open position, such that the main interlock disc is rotatable to push the respective interlock pin (174, 174') to engage with the third groove on each of the at least one earthing switch interlock disc (173, 173') respectively to stop each of the at least one earthing switch interlock disc (173, 173') from rotating so as to lock the movable contact of each earthing switch (12, 13) in the open position while the movable contact of the disconnector is moved to a closed position.