Patent GB-191505201-A (GB)
Title: Improvements in and relating to Circuit Breakers, Current Limiters, Excessive Current Indicators and the like for Electric Circuits.
Inventor: MURRAY ETHELBERT THOMAS RUTHVE
IPC: H01H71/24
Filed: 1915-04-06
Abstract: 5201. Murray, E. T. R., and Shotter, G. F. April 6. Electro-magnetic switches; electrically tripped and released switches.-Relates to electro-magnetically-actuated current-limiting devices adapted to interrupt the circuit or include in it a " dimming " or other resistance only in the event of a persistent, predetermined overload. According to the invention, an alternative circuit controlled by an alternative switch is provided in parallel with the main circuit through the automatic switch. The main switch arm 1 pivoted at 2 and co-operating with the mercury cup 10 is provided with an armature 33 having a hooked end 32 engaged by a spring catch 29 whereby the arm is held in the closedcircuit position against the action of the overbalancing weight 3. The alternative switch arm 5, pivoted at 6, and co-operating with the mercury cup 11, is over-balanced so as normally to assume the closed circuit position. The arms 1, 5 have extensions 42, 41 engaging below a pivoted lever 38 provided with a contact 40, and the arm 1 has an extension 43 engaging above the lever 38. The main switch arm is released on the occurrence of a predetermined overload, through the coil 17, by the attraction of the cam-adjusted armature 21, the adjustment of which is indicated by the pointer 26, the armature engaging a pin 28 and lifting the catch 29. The arm 1 now swings into the open position but the main circuit is still closed through the short-circuited re-setting-coil 4 and through the switch arm 5; the extension 43 of the arm 1 at its extreme open position engages the lever 38 and withdraws the contact 40 from between the contacts 19, thereby removing the short-circuit from the re-setting-coil 4 of the switch arm 1 so that the arm 1 is brought back to its closed position. During the final part of this movement, the extension 42 strikes the lever 38, closes the short circuit of the coil 4 and imparts through the lever 38 a blow to the extension 41 which serves to swing the alternative switch arm 5 into the open position from which it descends to the closed position. During this sequence of movements, one or other of the switches has been closed so that the overload, which it is assumed has ceased before the main switch regained its closed position, has been ineffective to open the circuit. If, however, the overload persists after the main switch has reached its closed position, the separation of the contacts 36, 37 by the closing movement removes a short-circuit from the electromagnet 17 and the armature 21 is again operated so as to release the main switch arm, which, together with the alternative arm, rises to the off position introducing a dimmer resistance 44 into the consumer's circuit. In a modification, instead of the current throngh both of the parallel circuits passing through the coil, only the current through the switch-arm 1 passes through the coil, and the re-setting-coil 4 is directly controlled by the switches 19, 40 instead of being short-circuited thereby. Specifications 28,947/09, 26,426/11, and 5200/15 are referred to.