The Furnas 21WE20A is an electromechanical lighting contactor used in commercial and industrial electrical control systems to switch lighting and other AC loads. It operates by energizing a control coil, typically 110–120 VAC, which closes the internal contacts to supply power to the load and opens them when the coil voltage is removed. The contactor is usually rated for about 20 amps and has multiple poles to control several circuits at once. It is commonly installed in lighting panels, motor control centers, and power distribution equipment. The design provides reliable and repeatable switching for building and facility electrical applications.