The MB30-SW-3P-1.2A-500V is a Mitsubishi molded case circuit breaker (MCCB) — 3-pole, rated 1.2 A continuous at 500 VAC. It's built for protecting branch circuits and smaller motor loads in industrial panels where a low amp rating is needed in a compact MCCB frame.
The 1.2 A continuous rating sets the thermal trip threshold for overload protection — sized for a small motor or a control transformer primary. The 500 VAC rating covers 480 V line-to-line common in North American industrial panels, with headroom for voltage sags.