GB214667A - Improvements in or relating to means for controlling electrically operated mechanisms and the like - Google Patents

Abstract

214,667. Whipp, F., and Whipp & Bourne, Ltd. Oct. 20, 1922. Electromagnetic switches, or other electromagnetically-operated mechanisms controlled from a distance by a three-position handoperated control switch g, as described in Specification 22646/12, are provided with an economy resistance for the maintaining circuit, in two parts, one of the parts being introduced into the operating circuit by the removal of a short-circuit therefrom before the operation is complete and, consequently, before the overload trip mechanism can come into operation. The arrangement avoids damage to the contacts of the overload trip switches in the event of faulty conditions arising while the control switch is held in the circuit closing position. As shown in the. Figure, applied to the control of a contactor, the resistance section d<1> is normally short-circuited by the auxiliary two-position switch e on the contactor. Consequently, for initial operation full voltage is put upon the operative winding a, but at the commencement of the movement, or at some short time after as determined by time-lag devices to prevent hunting the short-circuit is removed. The overload trip contacts c operated by the overload coils b cannot effectively close a short-circuit on the operating winding until the switch e closes its upper contacts thereby ensuring that the resistance section d' is in series with the winding a before the short circuit thereon for automatic release is introduced. Both sections d<1>, d<2> are inserted in the maintaining circuit when the auxiliary contacts f of the contactor close.