Square D 8903SM011 is a lighting contactor used in commercial and industrial electrical systems to switch large electrical loads such as lighting circuits or other power equipment. It operates with an electrically energized control coil, which when activated closes the main power contacts to supply current to the load, and when de-energized opens the contacts to interrupt power. This contactor is designed for frequent switching and reliable performance in panelboards, lighting control centers, or motor control applications. It has multiple poles so it can switch all phases of a three-phase circuit at once, and its rugged construction supports long service life in demanding environments. It is commonly used where remote or automatic load control is required.