MCCB with ETU350 — selectivity and headroom
The Siemens SENTRON 3VA2225-6HN32-0AE0 is a 3-pole molded case circuit breaker rated for 250 A continuous current (Iu) with an ETU350 electronic trip unit. Breaking capacity hits 242 kA at 240 V and 187 kA at 415 V — that's the kind of SCCR headroom you need for high-fault distribution panels or transformer secondaries where a standard MCCB would cascade upstream. The ETU350 gives you adjustable long-time, short-time, and instantaneous protection curves, so you can coordinate downstream breakers without nuisance trips. Rated insulation voltage is 800 V, and the breaker carries 4 auxiliary switches (HQ type) for status feedback to a PLC or annunciator panel. No undervoltage release, no ground-fault module, no communication function — this is a straight line-protection device, not a smart breaker. If you need those options, you'd step up to the 3VA2 with the communication-capable trip unit.
Thermal derating and panel fit
The 250 A rating holds flat up to 50 °C ambient; at 55 °C it derates to 241 A, and at 70 °C it's 213 A. That matters when you're stuffing this into a crowded enclosure with other heat sources — the thermal curve is in the datasheet, but the takeaway is you don't lose headroom until you're past 50 °C. Dimensions are 181 mm high, 105 mm wide, 86 mm deep — standard 3-pole MCCB footprint for a 250 A frame. Front protection is IP40, so it's fine for a clean indoor panel but not for washdown. Maximum power loss is 48 W — that's the heat you need to vent. If you're panel-building, account for that in your thermal budget. The auxiliary contacts are pre-wired from the factory, so no field-assembly of the switch block.