21 AUTOMATIC ELECTRICAL SWITCHES; MAGNET AND SOLENOID OPERATED SWITCHES AND RELAYS; AND ELECTRONIC CONTROL EQUIPMENT-NAMELY, SWITCHES AND RELAYS, SOLID STATE SWITCHES AND RELAYS, SYNCHRONIZERS, REVERSE POWER AND REVERSE CURRENT SWITCHES AND RELAYS, SENSORS, POWER TRANSFER SWITCHES, AND SOLID STATE VOLTAGE, FREQUENCY, AND CURRENT MONITORS