The ABB S203-B10 is a 3-pole miniature circuit breaker rated for 10 A with a Trip Curve B characteristic, meaning it trips between 3 and 5 times rated current — suited for resistive or lightly inductive loads where short inrush is minimal. It interrupts faults up to 10 kA at 277 VAC, giving you enough SCCR headroom for most distribution sub-panels without cascading upstream.
Panel fit and sourcing
The 3-pole format occupies three module widths, so factor that into your enclosure fill count.
Curve B vs Curve C — the real difference
The S203-B10 uses Trip Curve B (3–5× In instantaneous trip), while the sibling S203-C10 uses Curve C (5–10× In). If your circuit has motor or transformer inrush that briefly exceeds 5× rated current, the B curve may nuisance-trip — that is the one case where stepping to the C10 avoids a callout. For resistive loads like heaters or lighting, the B curve gives faster fault clearing, which is the better choice.