The Siemens 3VA1225-6GF42-0AJ0 is a SENTRON molded case circuit breaker (MCCB) in the line-protection version, carrying 250 A rated continuous current (Iu) across four poles. The TM240 thermal-magnetic release handles overload and short-circuit protection without an electronic trip unit — no voltage trigger, no ground-fault monitoring, no communication module. This is the fixed-thermal, fixed-magnetic variant, sized for straightforward feeder or main-switch duty where adjustable trip curves aren't required.
Breaking capacity and selectivity headroom
Rated breaking capacity hits 220 kA at 240 V, dropping to 154 kA at 415 V, 36 kA at 440 V, and 17 kA at 690 V. At 415 V — the common industrial distribution voltage — 154 kA gives substantial SCCR headroom for high-fault panels. That level supports full selectivity with downstream 50 kA or 65 kA MCCBs without forcing a series-rated compromise; the upstream breaker clears before the downstream device reaches its limit. The 690 V figure (17 kA) matters for 600 V class installations in North American or marine plants.
Thermal derating and ambient temperature
Rated continuous current holds at 250 A from 40 °C through 50 °C ambient. Above that, derating begins: 243.3 A at 55 °C, 236.5 A at 60 °C, 229 A at 65 °C, and 223 A at 70 °C. In a sealed, non-ventilated enclosure near other heat sources, the 55 °C or 60 °C column is the realistic operating point — size the downstream conductor and bus for the derated figure, not the nameplate 250 A. The thermal-magnetic release (TM240) is calibrated at 40 °C; the thermal element tracks ambient, so in a hot panel the breaker trips earlier on overload, which is the intended behavior.
Physical fit and panel integration
Dimensions: 158 mm height, 140 mm width, 70 mm depth. Four-pole frame, so width is the critical slot dimension — 140 mm matches the standard 4-pole MCCB cutout in most Siemens SENTRON and ALPHA distribution panels. The IP40 front protection means it is rated against solid objects over 1 mm but not sealed against moisture; install in a dry indoor enclosure or add a gland plate for washdown areas. Auxiliary contact version ships with 2 auxiliary switches plus 1 trip alarm switch (HP type), which fits standard SENTRON accessory slots without additional wiring adapters.