Branch-circuit protection for three-phase panels
The ABB S203-B40 is a 3-pole miniature circuit breaker rated at 40 A with a Trip Curve B characteristic, meaning it trips at 3–5× rated current — suited for resistive loads, lighting circuits, and lightly inductive equipment where inrush is modest. DIN-rail mount snaps into standard 35 mm rail, so it integrates directly into an existing panel without adapter hardware.
Curve B vs. other trip curves
Trip Curve B (3–5× In) is the correct choice when the load draws minimal inrush — think lighting banks, resistive heaters, or general-purpose outlets. If the downstream equipment includes motor starters or transformers with higher magnetizing inrush, a Curve C (5–10× In) or Curve K (10–14× In) breaker would be specified instead. The S203-B40's 40 A frame and 10 kA SCCR at 277 VAC are shared across the S200 series; the curve is the deciding factor for coordination.