What it is and what it does
Siemens SENTRON 3VA1225-5GF42-0AG0 is a 4-pole molded case circuit breaker (MCCB) sized at 250 A continuous, with a TM240 thermal-magnetic overcurrent release. It's built for line protection — main feeder or large subfeed in a distribution panel, not motor-starting duty. The frame is rated 800 V insulation voltage, so it handles 480Y/277 V or 600 V delta systems without derating the insulation. Power loss runs 57 W max at full load — that's the heat the enclosure has to vent. It carries a built-in auxiliary switch plus a separate trip-alarm switch, so the PLC or BMS gets a discrete signal when the breaker trips on fault — no add-on module needed for that.
Breaking capacity — the real SCCR story
This MCCB clears 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, 30 kA at 500 V, and 17 kA at 690 V. That's the interrupting capacity at each voltage level — what matters for the available fault current at the panel's point of common coupling. At 480 V (common US industrial distribution), the curve lands between the 415 V and 440 V figures — roughly 100 kA class. That's high enough for most secondary-side service entrances without needing a current-limiting fuse upstream.
Thermal derating — don't size it by the label alone
Rated 250 A continuous at 40 °C, 45 °C, and 50 °C — no derating needed up to 50 °C ambient inside the enclosure. At 55 °C it's 243 A, at 60 °C it's 237 A, at 65 °C it's 230 A, and at 70 °C it's 223 A. If the panel sits in a hot mezzanine or near a furnace line, the 70 °C figure (223 A) is the one to use for sizing. The storage range (-40 °C to 80 °C) covers shipping and warehouse extremes without issue.
Fit in the panel — dimensions and mounting
Footprint: 140 mm wide, 158 mm tall, 70 mm deep. That's a 4-pole frame in the 3VA platform — wider than a 3-pole, so check the existing DIN-rail or mounting-plate layout before you swap. Depth of 70 mm (2.76 in) means it fits standard 600 mm deep enclosures with clearance for rear-connected busbars or cable lugs. The wireman needs access to the front terminals and the TM dial — no side-access required.