The Siemens SENTRON 5SQ2170-2YA25 is a 1-pole miniature circuit breaker (MCB) with a C-curve trip characteristic rated at 25 A. It provides a 3 kA breaking capacity per EN 60898 at 240 V AC, making it suitable for protecting lighting, socket-outlet, and general-purpose branch circuits in residential and light commercial distribution boards. The 1-module-width (1 MW) footprint and 55 mm installation depth mean it snaps directly onto a standard DIN rail in a consumer unit or sub-distribution panel — no extra space needed for the neutral pole since this is a single-pole device.
The C-curve trips between 5 and 10 times rated current — so a 25 A C-curve holds through motor inrush up to about 250 A but clears a hard short fast. The 3 kA breaking capacity per EN 60898 means it safely interrupts a fault current up to 3 kA at 240 V AC; if your prospective short-circuit current at the panel exceeds that, you need an upstream current-limiting device or a higher-rated MCB. The 25 A rating at 30 °C derates to 20 A at 60 °C — so if the breaker lives in a hot enclosure (e.g., next to a transformer or in a sun-exposed panel), size the load accordingly.
Single-module width on a DIN rail. The 55 mm depth is shallower than the older 5SJ3 series (70 mm) — so if you're retrofitting into a panel originally built for 5SJ3140-7, the 5SQ2170-2YA25 leaves an extra 15 mm behind the breaker for wiring or busbar clearance. Pollution degree 3 and overvoltage category 3 mean it's rated for the typical industrial environment inside a distribution board — conductive dust and transient overvoltages up to 4 kV are within spec. No neutral switching on this 1P variant; the neutral bar passes through separately.