What this breaker is and what the ratings mean
The Siemens SENTRON 3VA1225-4EF32-0AC0 is a 3-pole molded case circuit breaker (MCCB) rated 250 A at 40 °C, designed for line protection — meaning it sits at the feeder or main distribution point, not downstream on a motor or branch circuit. The 250 A rating holds flat from 40 °C to 50 °C, then derates to 243 A at 55 °C and 223 A at 70 °C (–), which matters if your panel runs hot or is in a non-climate-controlled enclosure. The TM240 thermal-magnetic release means the thermal trip follows a 240 A frame curve; the magnetic instantaneous pickup is fixed, not adjustable. This is a standard panelboard or switchboard MCCB — no communication function, no ground-fault monitoring, no undervoltage release.
Interrupting capacity — the number that decides selectivity
This breaker's interrupting capacity changes significantly with system voltage. At 240 V it's rated 121 kA; at 415 V it drops to 75.6 kA; at 440 V to 52.5 kA; at 500 V to 17 kA; and at 690 V to 11.9 kA. For a 480 V panel (common in North America), interpolating between 440 V and 500 V gives roughly 35–40 kA available — adequate for most industrial services, but if your transformer feeds a high-fault bus (say 65 kA at 480 V), you'll need to step up to the 3VA2 high-capacity frame or add a current-limiting fuse ahead. The insulation voltage is rated 800 V, so the breaker is electrically safe for 690 V systems, but the interrupting capability at that voltage is limited to 11.9 kA.
Integration — panel fit and wiring
The 3VA1225-4EF32-0AC0 mounts on a DIN rail or bolts directly into a panel base. Dimensions are 105 mm wide, 158 mm high, 70 mm deep. The 105 mm width is three 35 mm pole pitches — standard for a 3-pole MCCB in a Siemens SENTRON panelboard or a generic distribution cabinet. The auxiliary switch configuration is listed as 2 auxiliary switches HQ, which provides two form-C contacts for remote status indication (open/closed/tripped). No trip indicator and no voltage trigger — if you need a shunt trip or undervoltage release, this variant doesn't carry them; order the appropriate -0AA0 or -0AB0 suffix. Power loss at rated current is 57 W maximum, so account for heat dissipation in a sealed enclosure.