What this breaker is and what the ratings mean
The Siemens 3VA1125-5EF42-0AA0-ZD00 is a 4-pole IEC frame 160 molded case circuit breaker with a 25 A thermal-magnetic trip unit (TM240, ATAM). The Icu rating of 55 kA at 415 V means it can safely interrupt a fault current up to that level without welding or rupturing — critical for high-fault installations like industrial switchboards or transformer secondaries. The overload protection band Ir=18...25 A and short-circuit protection Ii=6.4...12.8 x In give you field-adjustable pickup, so you can dial in the trip curve to match motor inrush or cable protection without swapping the breaker.
Deployment context
The 3VA1 frame mounts on a DIN rail or panel base inside a control cabinet. The 4-pole configuration with an unprotected neutral conductor suits it for three-phase + N systems where the neutral does not require overcurrent protection — common in North American and IEC distribution panels. The nut keeper kit is a small but useful detail: it keeps the terminal hardware captive during wiring, saving time on a panel build.