The MGP36500SA is a Square D PowerPact M unit mount breaker with electronic trip, rated 500A, 3-pole, 18kA at 600VAC, and includes a shunt trip at 120V and lugs off end. This is a unit mount style — mounts directly to the panel or switchboard bus, not a DIN-rail or plug-in base.
The 500A continuous rating and 18kA interrupting capacity at 600VAC define its fault-clearing capability. In a panel, this breaker sits downstream of a main that can deliver up to 18kA symmetrical — if the available fault current at its line side exceeds that, coordination requires a current-limiting fuse or a higher-rated upstream breaker. The electronic trip gives adjustable long-time and short-time pickup and delay, plus instantaneous settings, so it can be tuned to coordinate with downstream branch breakers. The shunt trip at 120V allows remote tripping from an E-stop or fire-alarm relay.