The Siemens SENTRON 5SQ2170-0KA40 is a 1-pole miniature circuit breaker (MCB) with a C tripping characteristic, rated at 40 A continuous current at 240 V AC, 50 Hz.
Snaps onto DIN rail. IP20 terminals, overvoltage category III, AC/DC up to 240 V. Energy limiting class 3 means this MCB limits the let-through energy (I²t) during a short circuit, reducing thermal stress on downstream wiring and connected equipment. That matters when coordinating with downstream loads — the breaker clears fast enough that the cable can be sized to the load current rather than the full fault current.