4-pole 125 A MCCB with TM240 release — what the ratings mean for your panel
The Siemens 3VA1225-5FF42-0AD0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels. It carries 4 poles rated at a continuous 125 A, with a TM240 thermal-magnetic overcurrent release — meaning the thermal element is calibrated for a 240 A frame, but the breaker itself is the 125 A tap. That matters for selectivity: the TM240 release gives you a higher short-time withstand before the magnetic trip fires, so you can coordinate downstream breakers without nuisance upstream tripping.
SCCR headroom by system voltage
Short-circuit current ratings (SCCR) vary significantly with system voltage — a key detail when you're specifying for a transformer secondary or a generator tie. At 240 V this breaker interrupts 187 kA; at 415 V it's still 121 kA; at 440 V it drops to 75.6 kA; at 500 V it's 30 kA; and at 690 V it's 17 kA. For a 480 V panel in North America (common 277/480 V wye), the 30 kA at 500 V covers most service-entrance requirements. The 690 V figure (17 kA) is relevant for 600 V Canadian or marine installations — verify your available fault current against that number.
Thermal derating — don't size by the 40 °C sticker alone
The breaker carries 250 A continuously from 40 °C through 50 °C, but above that it derates linearly: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If your panel ambient hits 60 °C (common in a packed enclosure with drives or transformers), you lose 13 A of headroom. The maximum operating temperature is 70 °C, and storage range is -40 °C to 80 °C. Power loss at full load is 57 W — factor that into your enclosure thermal budget.
Physical fit and integration
Dimensions are 158 mm high × 140 mm wide × 70 mm deep — a standard 4-pole MCCB footprint for Siemens SENTRON 3VA2 frames. It mounts on a DIN rail or directly to a backplate via the screw terminals. The design includes provision for 3 auxiliary switches (HQ type) if you need remote status. No undervoltage release, no ground-fault monitoring, no communication function on this variant — it's a straight thermal-magnetic line protection breaker.