A three-position disconnector switch, comprising: - a power in contact ; - a piston ; - a power out contact ; - a plurality of flexible locking elements ; - an earthing contact ; and - a threaded rod ; wherein a length of the piston is such that in a first switch position an outer surface of a wall of the piston makes an electrical contact between the power in contact and the power out contact; wherein the length of the piston is such that in a second switch position the outer surface of the wall of the piston does not make an electrical contact with either the earthing contact or the power in contact, and wherein in the second switch position the outer surface of the wall of the piston makes an electrical contact with the power out contact; wherein the length of the piston is such that in a third switch position the outer surface of wall of the piston makes an electrical contact between the earthing contact and the power out contact; wherein the piston comprises an inner threaded section configured to engage with the threaded rod, and wherein rotation of the threaded rod is configured to engage with the inner threaded section to move the piston along an axis of the switch between the different switch positions; wherein the piston comprises a groove extending in a direction parallel to the axis; wherein each of the flexible locking elements is configured such that a part of each of the flexible locking elements moves into and out of the groove as the piston is moved along the axis of the switch between the different switch positions as the piston is moved in both directions along the axis; wherein, as the piston is moved along the axis the switch is configured such that there is always a part of at least one flexible locking element in the groove; and wherein when a part of at least one flexible locking element is in the groove the piston is constrained from rotating about the axis. - a power in contact ; - a piston ; - a power out contact ; - a plurality of flexible locking elements ; - an earthing contact ; and - a threaded rod ; wherein a length of the piston is such that in a first switch position an outer surface of a wall of the piston makes an electrical contact between the power in contact and the power out contact; wherein the length of the piston is such that in a second switch position the outer surface of the wall of the piston does not make an electrical contact with either the earthing contact or the power in contact, and wherein in the second switch position the outer surface of the wall of the piston makes an electrical contact with the power out contact; wherein the length of the piston is such that in a third switch position the outer surface of wall of the piston makes an electrical contact between the earthing contact and the power out contact; wherein the piston comprises an inner threaded section configured to engage with the threaded rod, and wherein rotation of the threaded rod is configured to engage with the inner threaded section to move the piston along an axis of the switch between the different switch positions; wherein the piston comprises a groove extending in a direction parallel to the axis; wherein each of the flexible locking elements is configured such that a part of each of the flexible locking elements moves into and out of the groove as the piston is moved along the axis of the switch between the different switch positions as the piston is moved in both directions along the axis; wherein, as the piston is moved along the axis the switch is configured such that there is always a part of at least one flexible locking element in the groove; and wherein when a part of at least one flexible locking element is in the groove the piston is constrained from rotating about the axis. <EOS>