GB147592A - Overload electric switches - Google Patents

Abstract

147,592. Krupp Akt.-Ges., F. May 15, 1919, [Convention date]. Protective arrangements; electro - magnetic switches.-An overload electro-magnetic switch is brought into the " off " position, against the action of a spring, by a tension coil normally connected up in series with a resistance so that the coil, although sufficiently energized to maintain the switch in the open position, is only active to produce the opening movement when the series resistance has been short-circuited by a separate overload relay energized by a current coil. In the arrangement shown in Fig. 1 for the overload protection of a direct-current motor B, the automatic switch D is controlled by the coil d<3> in series with the resistance F. The relay E carries the motor current and on overload bridges the contacts e<2>, e<3> which short-circuits the resistance F whereupon the motor circuit is broken at the contacts d<1>, d<2>. After a short delay imposed by the short-circuited winding e<5> on the relay core, the resistance is again inserted and the automatic switch retained in the " off " position by the reduced current. To re-establish the motor circuit, the hand switch C is opened whereupon the coil d<3> is de-energized and the switch is drawn to the closed position by the spring d<4>. The core of the switch may carry an additional bridging contact in the short-circuit for the resistance F and in series with the contacts e<2>, e<3>.