493,648. Electromagnetic relays. RYDER, C., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. May 31, 1937, No. 15125. [Class 38 (v)] Springs, arrangement of ; switches, latching and unlatching.-A switchgear installation comprises in combination with a remotely-controlled main switch of the switchgear proper, a plurality of auxiliary switches for controlling auxiliary circuits involving interlocks and indicating devices at or in the neighbourhood of the remote place of control, the auxiliary switches being disposed together with said devices and circuits at or in the neighbourhood of said remote place of control, and mechanically coupled with an electric servomotor located adjacent the auxiliary switches. The servomotor-operating circuits are associated through pilot wires with switch means disposed adjacent the main switch andmechanically coupled therewith so as to be actuated by movement of the main switch to cause operation of the servomotor to actuate the auxiliary switches in accordance with the movement of the main switch. Fig. 2 shows a control circuit extending over pilot wires 29, 30 from the switch 31 operated by the main switch to the reversing-switch and windings of the servomotor itself, the latter and the auxiliary switches being shown in Fig. 1, in which the switches are in the form of contacts 4.. 6 mounted on a drum 2. The drum, servomotorarmature 8, and a disc 19 are fast on a shaft 3, the rotation of which in either direction is limited by the engagement of an arm 26 on the drum 2 with fixed stops 27, 28. Disc 19 is pivoted to an over-centre spring arrangement 22, 23, and is notched at 20 to receive a rod 21 on an arm 12, which is freely mounted on shaft 3 and carries change-over contacts 13, 14 co-operating with contacts 15, 16 and 17, 18, respectively. The engagement at 20, 21 is such that when the armature 8 is rotated anticlockwise, its stroke is almost completed before it operates arm 12, and similarly in moving back to the position shown. The armature carries a winding 11 which is connected across contacts 13, 14. If the main switch is closed, switch 31 is moved to the dotted position to energize the armaturewinding 11 and field-winding 10 in series over pilot 29 and contacts 15, 17. The armature is thereby moved to its other position and at the end of the movement, changes over contacts 13, 14 to the dotted position in which they engage contacts 16, 18, so breaking its own circuit. When the main switch is opened, switch 31 is moved back to the full-line position to energize the windings 11, 10 in series over pilot 30, and as in these positions of contacts 13, 14 the current traverses winding 11 in the opposite direction, the armature 8 rotates back to its original position, thus restoring contacts 13, 14 to their original position. In Fig. 3, the change-over switch of the servomotor comprises a pair of mercury-containers on or coupled to the armature 8. When switch 31 is moved to the dotted position, a circuit is made over pilot 30, contacts 39 and mercury 37, from left to right in winding 11, contacts 38 and mercury 36, and field winding 10. Armature 8 is rotated anticlockwise but owing to centrifugal force acting on the mercury, the circuit is not broken at 38, 39 until the armature has completed its stroke. When 31 is moved back, contacts 40, 41 are bridged and winding 11 traversed by current in the opposite direction. The over-centre arrangement of Fig. 1 may be replaced by the locking arrangement of Fig. 4, comprising a disc 42 fast on shaft 3 and provided with notches 43, 44 co-operating with a spring-controlled locking-arm 46 in the extreme positions. The winding 51 for raising arm 46 is in series with winding 10 so as to be energized and deenergized therewith. In a modification of this last arrangement, Fig. 6 (not shown), each of a pair of locking-levers has a recess co-operating with a projection on the disc, their operating magnets being connected in the respective pilots 29, 30, so as to be alternately energized to unlock the disc.