Automatic transfer switch

Abstract

An automatic transfer switch comprising a pair of molded case switches, a novel cam drive mechanism and a lever linkage is provided to assure a programmed timed sequence of contact transfer so that arc extinction is achieved in load transfer and re-transfer between normal and emergency power sources, thereby preventing source to source short circuits. To prevent motor override from disturbing the cam during stopping, declutching or escapement means is provided to separate the drive pin in the cam plate from the motor drive. Improved transfer for motor loads may be achieved by additional escapement and time delay intervals in the transfer between normal and emergency sources. To facilitate the starting and stopping of the motor drive, auxiliary contact means are provided which coact with the outside periphery of the cam plate to open and to close the incoming power for the electric motor drive. The toggle of each molded case switch is positioned in precise relationship by the cam mechanism to insure that only one toggle is in the on position at any one time. An auxiliary mechanical interlock which is operated by the molded case switch contacts is provided to assure that contacts of the two molded case switches cannot be closed simultaneously. Load connectors can be mounted to either the top or bottom of a novel bus bar arrangement which allows easy attachment of incoming load cables. An easily detachable mounting for the two molded case switches on the vertically extending bus bars is provided whereby both molded case switches can be replaced without the disconnection of external power conductors.