The Siemens 5SY4120-6KK11 is a 1-pole SENTRON miniature circuit breaker with a B tripping characteristic, rated 20 A at AC. It delivers a 10 kA breaking capacity per EN 60898 and 20 kA per IEC 60947-2, so it handles standard residential and light industrial fault levels while offering headroom under the higher IEC standard for industrial panel coordination.
What the ratings mean for fit
The B-curve (tripping between 3 and 5 times rated current) is the standard choice for resistive and general-purpose loads — lighting, socket outlets, control transformers — where inrush is modest. At 20 A it feeds a 4–5 kW resistive load on a 230 V single-phase circuit. The 18 mm width (1 modular unit) snaps into any standard DIN-rail distribution board, and the 76 mm depth plus 70 mm installation depth fits flush in shallow enclosures. Temperature derating is built in: at 40 °C the breaker is rated 18.78 A, dropping to 16.08 A at 60 °C. If the panel ambient runs hot, factor the 60 °C figure into the load calculation rather than the 20 A nameplate. Pollution degree 3 and overvoltage category III mean the breaker is rated for fixed installations inside industrial control panels where conductive dust or condensation may be present — not just clean residential environments.