What it is and what it does
The Siemens 5SY5214-7KK11 is a 2-pole miniature circuit breaker from the SENTRON series, designed for universal current (AC/DC) operation with a C tripping characteristic and a rated current of 0.3 A at AC. It breaks fault currents up to 10 kA per EN 60898 on AC and 10 kA per EN 60898-2 on DC at 440 V. The C-curve means it trips between 5 and 10 times rated current — standard for moderate inrush loads like small transformers or lighting banks where you want nuisance-free protection without the delay of a D-curve.
Panel fit and mounting
Snaps onto DIN rail via the quick assembly system — 2 modular width units (36 mm wide). Depth is 76 mm, installation depth 70 mm, height 90 mm.
Temperature derating — the real-world current
The 0.3 A rating holds at 35 °C ambient. Above that, it derates: 0.28 A at 40 °C, 0.27 A at 45 °C, 0.26 A at 50 °C, 0.25 A at 55 °C, and 0.24 A at 60 °C. If your panel runs hot — say a packed enclosure near a drive or transformer — size the load to the derated figure, not the nameplate. The operating range spans -40 °C to 75 °C, so cold starts in unheated shelters are fine.