What it is and what the ratings mean for fit
The ABB S201-D40 is a 1-pole miniature circuit breaker rated 40 A with Trip Curve D, meaning it's designed for loads with high inrush currents — motor starters, transformers, or solenoid banks — where the magnetic trip threshold (10–20× In) prevents nuisance tripping on startup. The 6 kA interrupting capacity at 277 VAC is adequate for most commercial supplementary protection applications; it safely clears a fault up to that level without welding contacts or cascading upstream. Rated 277 VAC line-to-neutral (or 480 Y/277 VAC three-phase), it covers common North American panel voltages. The DIN-rail footprint snaps into standard 35 mm rail — no adapter needed, and the finger-safe terminals accept stranded or solid copper without ring lugs. Listed as UL 1077 supplementary protector and CSA 22.2 No. 235, so it's recognized for use within an end-use equipment enclosure — not as a service-entrance disconnect, but as branch-circuit protection inside a control panel or machine. That distinction matters when the inspector reads the nameplate.
Lifecycle and sourcing reality
Sourced to order through independent distribution. Availability and current pricing confirmed at quote time against an RFQ. The UL/CSA listing means compliance documentation (RoHS, REACH, UL file) is standard with the shipment.