Square D 8903SM012 is an industrial lighting contactor used to switch large electrical loads such as commercial lighting circuits, fans, or other power equipment. It operates by energizing a control coil (commonly 120 V AC) to pull in the main contacts and allow current to flow to the load, and de‑energizing the coil to open the contacts and interrupt the circuit. The “8903” series is designed for frequent switching and reliable operation in panelboards, motor control centers, or lighting control systems. This type of contactor has multiple poles so it can switch all phases of a three‑phase circuit simultaneously. It is built for durability and extended service life in demanding electrical environments.