394,560. Oil-break switches. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION, WHITNEY, W. B., WEDMORE, E. B., and GOSLAND, L., 36, Kingsway, London. Feb. 1, 1932, Nos. 30690/32 and 1234/33, (divided on 389, 882), 30564/32, and 36347/32. [Class 38 (v).] Arc-rupturing devices; switches, actuating.- A circuit-breaker or other circuit-interrupter, which is arranged for the rupture of the arc to be assisted by means of energy in the circuit to be interrupted, and for the arc to be formed in an enclosed space having one or more outlets for the arc products to assist in rupture of the arc, is provided with a control member such as. a gate, shutter, or intermediate electrode which is arranged to render the total effective crosssectional area of vent for products from a part of the arc path after the completion of a first stage of electrode movement smaller than the total effection cross-sectional area of vent during that first stage of the electrode movement. The breaker is preferably furnished with a chamber in which the arc is first drawn, and which by reason of its total vent area is adapted to extinguish arcs at the higher end, but not at the lower end, of the circuit range, and with a second chamber into which low current arcs are drawn and which is adapted to extinguish arcs at the lower, but not at the higher, end of the circuit range, the two chambers being separated by a movable gate either affording a restricted passage for the arc or entirely separating the chambers. In the latter case, the arc is continued into the second chamber as an arc in series with that in the first chamber. Fig. 1 shows a structure generally similar to that of Fig. 1 of Specification 366,998, and comprising an upper or main chamber in which large current arcs are ruptured by being driven by the pressure set up in the oil or other liquid in the chamber by the arc itself, out of the orifices 2 in alternate baffles. Contact is finally broken at the element 1a of the fixed contact, the other elements 1 having insulating tips 14 of vulcanized fibre or "Mycalex," whereby the arc is set up as near to the outlets 2 as is possible. The gate is in the form of a hinged and spring- controlled flap 15 located immediately above a baffle 10, and is formed to provide a space 19 and recess 20 in its under surface whereby a restricted passage for the arc is formed, but if the gate is of conducting material it may completely separate the lower chamber from the upper, a series arc being thereby drawn in the lower chamber. The gate acts on the moving contact (not shown) to hold it in its opening movement against the outlets 2 and when that contact is sufficiently retracted, closes to the position shown. Hence the arc drawn below the gate can only escape through the outlets 2 in the baffles 12 in the lower chamber, those outlets being preferably, but not necessarily of narrower width than those of the main chamber. In Figs. 9, 11, all the baffles are formed with superposed, registering apertures constituting a passage 23 into which the arc space in the lower chamber leads by way of outlets 24. The arc products driven from the lower chamber are thereby caused to sweep across the arc in the upper chamber. The products may be cooled either by arranging for the passage 23 to be of increasing cross-section upwards, or by arranging a finely-perforated plate in the passage at the level of the gate, or both. A further gate 25 maintains the arc against the outlets 24. Ina further form, Figs. 12-14 (not shown), the outlets from the lower chamberare arranged on the same side as those of the upper chamber but lead into ducts passing circumferentially round to the passage 23. In this form, shallow recesses may be cut in the under surfaces of such baffle-plates as are not provided with outlets, those recesses registering with the ducts so as to allow arc gases to pass freely over any oil that may be in the ducts. To prevent the gate 15 from opening by the pressure in the lower chamber, it may be provided with a self-acting latch which is moved aside by the moving contact when the switch is being closed. In another form, Fig. 15 (not shown), the gate is arranged as an intermediate movable contact carrying contactmembers similar to 1, 1a and adapted completely to fill the baffle opening in which it slides. In opening, this intermediate contact remains in contact with the main movable contact until it is arrested by the baffle supporting it and an arc is drawn between it and the fixed contact proper. The subsequent arc, if any, is produced between it and the main movable contact in the lower chamber where the openings are small enough to enable the arc to be extinguished. In Fig. 16 there is used a shutter 31 similar to that of Fig. 9 of Specification 375,808, this shutter being held in the position shown by an arm 33 and a latch 39 which in turn is under control of a member 44. When, in opening, the movable contact passes below the member 44, the latter is moved to the right by a spring 42 and at the same time the shutter 31 is pushed down by a spring 37 until it bears on a stop 38 and closes the openings 2 to the required degree. A similar arrangement can be carried out using a pair of jaw members to define the throat of the outlets 2, the jaws being arranged to be contracted to diminish the throat opening by means of a toggle system operated at a given part of the opening movement of the movable contact, Figs. 17-19 (not shown). Instead of being arranged to one side of the arc path, the vents may be arranged about the contacts themselves ; thus, that in the upper chamber may be arranged about the fixed contact and that in the lower about the movable contact, but side outlets are not precluded provided they conform to the principle of the invention, Fig. 22 (not shown). The opening movement of the contact may be a continuous one, in which case the contact is arranged to traverse each stage in a cycle so as to meet the condition that an asymmetrical wave may possibly have only one zero point per cycle. Preferably, however, to reduce the length of stroke, the contact is arranged to pause for a cycle at the end of each stage in rupturing asymmetrical currents or for a halfcycle with symmetrical currents. This pause may be effected by means of a cam rotated by the operating member and having a surface which allows the contact, to move through one stage, then pause, then move through the next stage. Another method is shown in Fig. 20 and employs a bridge-member 59 carrying a rod 72 to which is pivoted an arm carrying a roller 70. The latter co-operates with guide surfaces on the structure 4 such that in opening circuit it first engages a surface 69 to depress the member 66 and movable contact 26, then at the point 73 moves without the contact, and on engaging surface 68 again takes the contact with it. A further modification of the invention consists in using two explosion pots, the movable contacts associated with which are carried by a bridge-member and adapted to break one after the other. The drawing of the two arcs may be separated by a pause or slowing- down, and the first arc to be drawn has access to a larger vent area than the second arc. In a further form, Fig. 23 (not shown), a series of flaps are released in turn by the movable electrode as it moves to the open position, the flaps serving to open vents of decreasing cross section. The invention may be combined with that of Specification 375,808, in which shutter openings are varied in accordance with the current to be interrupted.