The Square D 8903SMG10 is a heavy-duty lighting contactor designed for commercial and industrial electrical systems. It uses an electrically actuated coil to open and close its main contacts, allowing it to control large electrical loads such as building lighting circuits, fan systems, or other power equipment. When the coil is energized (often with a standard control voltage like 120 V AC), the contactor pulls in the contacts to supply power; when the coil is de-energized, the contacts open to interrupt the circuit. The 8903SMG10 has multiple poles for switching all phases of a three-phase load simultaneously and is built for frequent operation and long service life. It is typically installed in panelboards, lighting control centers, or motor control centers where remote or automatic load switching is needed.