It's a UL 1077 supplemental protector, meaning it's intended for branch-circuit protection inside listed equipment — not as a service-entrance main breaker. Rated 277 VAC line-to-neutral on a 480Y/277 V wye system, so it covers the common North American lighting and control panel voltage.
The 3-pole width (about 54 mm for three modules) fits a standard panel layout. No special busbar — the S200 series uses a common pin-and-fork bus system for feed-through or group supply. Verify the busbar pitch matches the S200 footprint before wiring.