The Siemens 5SL6514-7 is a SENTRON miniature circuit breaker rated 0.3 A at 230 V AC, with a C tripping characteristic and a 6 kA breaking capacity per EN 60898 and IEC 60947-2. It's a 1P+N (switched neutral) unit in a 36 mm wide, 2-module-width housing — that's two standard DIN-rail slots. Current-production part, so no last-time-buy scramble.
At 0.3 A, this is a low-current branch; you'd see it on a control transformer secondary, a PLC power supply feed, or a signal-conditioner loop. Derate the 0.3 A rating at elevated ambient: 0.28 A at 40 °C, 0.25 A at 55 °C — factor that into your wire sizing if the breaker lives in a warm enclosure. The 1P+N configuration switches both phase and neutral, with the neutral pole opening after the phase pole — important for isolation on single-phase circuits where you want guaranteed disconnection of both conductors. The neutral conductor switching feature is built in, so no separate neutral disconnect block needed. Touch protection is integral;
The 10,000 typical mechanical operating cycles is the expected life under normal switching; this isn't a daily-switch-duty device, but it'll handle occasional manual operation for decades.