GB276465A - Improvements in or relating to electric circuit interrupters - Google Patents

Abstract

276,465. Jackson, L. Mellersh-. (Shoenberg, M. H.). June 18, 1926. Thermal interrupters, adapted to be removably positioned within an electric lamp socket, comprise a relatively flat casing containing an interrupter element. The latter is preferably a bimetallic strip actuated by a heating resistance. Fig. 1 shows the position of the removable interrupter 10 in a lamp socket, the opposite contacts 16, 17 of the interrupter engaging the socket contact 12 and lamp contact 13. The interrupter comprises a casing in two insulated telescoping halves 18, 19 which are recessed at 46, 47 to engage one contact of the interrupter proper and a disc 24 on which it is mounted. The interrupter proper comprises a bimetallic strip 28 mounted on an upset part 29 of the disc so as to lie along a recess 26 of the latter, the recess lying to one side of the centre so as to avoid undesired contact with the casing. To the strip is secured one end of a heating resistance 30, preferably enamelled chrome-nickel alloy, which is wound on insulation 31, the thickness of which determines the period of the interrupter. A contact 33 on the end of the strip engages a fixed contact 34 on a spring plate 36 which is insulated by a mica plate 37 and washer 40 from the disc 24 to which it is secured by an eyelet 38. The plates 36, 37 are positioned by means of upset parts 42 on the disc engaging holes in the plate 37. The end of the plate 36 is turned up to form a contact 43 and the contact 33 is of silver or platinum or other non-oxidizing metal. The strip may be in shunt to the coil or in series, and the latter is made of a resistance of greater value than that of the smallest lamp it is required to control, so that the interrupter may be used with a large range of lamps. In the shunt connection the free end of the coil is connected to the contact 34 so that when the strip is heated, the circuit to the lamp is made direct and that to the coil is shunted. The strip on cooling down " breaks " the direct lamp circuit and removes the shunt from the coil so that it heats up again. In the case of the series connection, the contact 33 is insulated from the strip and connected to the free end of the coil which, on heating up, breaks its own and the lamp circuit. The spring contacts 16, 17 made of copper or phosphor bronze and formed of a disc split at 49 along an arcuate line to form a contact part 50 and an inner disc which is secured to the casing by spot welding as at 47. Interfitting insulating cups 52, 53, provided with central apertures for the contacts, are placed over the casing and cemented together, or, alternatively, the casing could be coated with vitreous or suitable enamel. The period of the interrupter may be varied by bending permanently either of the strips 28 or 36, and owing to the metallic nature of the disc heat storage will tend to stabilize operation. Owing to the low resistance of the coil when the contacts separate arcing is reduced and rapid operation at high currents is obtained. If very rapid or very slow operation is desired, the amount of insulation 31 on one side of the strip may be increased, so reducing the rate of heat transfer on that side.