225,963. British Thomson-Houston Co., Ltd., and Fitzgerald, A. S. Sept.. 22, 1923. Automatic circuit-breakers ; actuating ; magnetic blow-outs.-A circuit breaker has a contactoperating armature on which an electromagnet having a single winding exerts two oppositelyacting magnetic forces, one of which predominates at relatively low excitation to bias the breaker to closed position and the other at relatively high excitation to effect the opening of the breaker. The preponderance of one force over the other depends on the inter-relation of the reluctance of a substantially closed magnetic circuit and the reluctance of a magnetic circuit containing an operating air-gap. As shown diagrammatically in Figs. 1 and 3, the coil 16 is arranged on the centre limb of an E-shaped core the upper limb. 23 of which is of greater reluctance and of less cross-sectional area than the lower limb 24 and carries a short-circuit winding 25 to act as a choke if the current in the coil 16 rises too rapidly. With a normal current in the coil 16 the armature 19 will be held against the upper limb owing to the air-gap 38, but on excess current the limb will become saturated so that the flux in the. lower limb and air-gap will attract the armature and open the switch. A spring 35 also acts to bias the switch to closed position when the switch is closed and acts on a lever 31 pivoted to the armature at 34 and to a fully extended or overset toggle 26, 27 at 29. The initial opening movement due to the flux in the lower limb causes the link 31 to move so that the spring 35 upsets the toggle and acts to assist opening of the switch. A series blow-out coil 15, shunt coils 17, and archorns are provided. Figs. 4 and 5 show a practical embodiment wherein the switch arm 44 is adjustably pivoted to the armature at 21 and the spring 35 is adjusted by means of a screw 48 and pivoted link 47. The value of the current at which the switch opens is, for a steadily rising current, adjusted by means of a pivoted magnetic member 51 controlled by a spring 53 and screw 54. The arc-horns 18 comprise copper members 41 arranged between slabs 42 of refractory material, .and the coils 15, 17 are arranged on the laminated yoke 43. To re-set the breaker, a lever pivoted near the end of the upper limb may engage, by means of a latch, the link 31 and/or the link 27 and/or the roller 56 and may be electromagnetically controlled. In order to provide a free trip, a cam or like device operable by the opening movement of the armature may disengage the re-setting latch. The Provisional Specification also states that the magnetic structure is mounted vertically on a panel with its limbs projecting away from the panel, that the fixed contact may be, resiliently mounted, and that, in the case of large currents, the coil 16 may be shunted across the main circuit. The biassing means may also be of a different nature, viz., a lever pivoted to the armature pivot, arranged parallel to the armature and biassed towards the panel; a latch pivoted to the panel, engaging the end of the lever and arranged normal thereto, and biassed downwards; a tension spring so arranged between the bottom of the lever and top of the armature as to bias the switch towards the closed position when the lever is engaged by the latch and the switch is closed, the armature carrying a stud which, on opening, lifts the latch, allows the upper end of the lever to move inwardly, and moves the spring on to the other side of the armature pivot, thereby holding the switch open. The switch may, further, be manually or mechanically operated by a movable system which is hinged on the armature pivot and engages the lever, and may be arranged for remote control by arranging a winding on the upper and central limb to produce a closing flux. Specification 7145/12 is referred to.