What the ratings mean for fit
The Siemens 3VA1125-3GE42-0AA0-ZD00 is a 4-pole IEC frame 160 molded case circuit breaker with a 25 A thermal-magnetic trip unit (TM220, ATFM). The headline breaking capacity is Icu=25kA at 415 V AC under breaking capacity class N — that means it can safely interrupt a fault current up to 25,000 A without welding or failing open, which is the standard requirement for most commercial and light industrial distribution boards in 400 V class systems. The overload protection is adjustable from 18 A to 25 A (Ir), and the instantaneous short-circuit pickup is fixed at 12.8 × In (320 A at the 25 A setting). The 100% N-conductor protection means the neutral pole is fully rated and protected, not just switched, so it's suited for 4-wire systems with significant neutral loading — common in data center or multi-phase rectifier feeds. The 3VA1 frame is a DIN-rail or panel-mount design for enclosure integration. Given the 25 A rating and 25 kA SCCR, it fits as a main or feeder breaker in a sub-distribution board, or as a branch protector for a 25 A motor circuit or a 25 A UPS bypass. The TM220 curve is a standard thermal-magnetic characteristic; it coordinates with downstream miniature breakers on most 10 kA rated panelboards.