250 A MCCB with TM240 release — selectivity and SCCR planning
The Siemens SENTRON 3VA1225-4GF42-0AC0 is a 4-pole molded case circuit breaker rated 250 A continuous, fitted with a TM240 thermal-magnetic overcurrent release. It is designed for line protection in distribution panels and motor control centers where you need to coordinate upstream and downstream devices. Breaking capacity runs 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, 17 kA at 500 V, and 11.9 kA at 690 V — enough headroom for most industrial service-entrance and sub-distribution applications where fault current is high. The TM240 release is a fixed thermal-magnetic type, meaning the thermal pickup and magnetic trip thresholds are factory-set for the 250 A frame. No field-adjustable electronic trip unit here — it's a straightforward overcurrent protector for fixed-load feeders or main breakers where you don't need LSIG or ground-fault options.
Thermal derating and power dissipation
Rated 250 A continuous up to 50 °C ambient. Above that, derate linearly: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If your enclosure runs hot — say a packed MCC bucket or a sun-exposed panel — factor that derating into your load schedule. Maximum power loss is 57 W at rated current. That's the heat you need to vent in a sealed enclosure; plan your thermal budget accordingly if you're stacking multiple breakers in a confined space.
Panel fit and dimensions
Mounts on a standard DIN rail or direct panel-mount. Dimensions: 70 mm deep, 140 mm wide, 158 mm tall. The 70 mm depth is relatively shallow for a 250 A frame — useful when gland-plate clearance or enclosure depth is tight. Insulation voltage rated 800 V. Operating temperature -25 °C to 70 °C; storage -40 °C to 80 °C.