What this MCCB carries and where it fits
The Siemens 3VA1225-4EF32-0AF0 is a SENTRON molded case circuit breaker (MCCB) rated for line protection, with a TM240 thermal-magnetic release and a 3-pole configuration. At 40 °C it carries 250 A continuous; the thermal derating curve drops to 223 A at 70 °C, which is the maximum operating ambient per the datasheet. The rated insulation voltage is 800 V, and the breaking capacity ranges from 121 kA at 240 V down to 11.9 kA at 690 V — so the voltage class of your distribution determines which interrupting rating applies.
Current derating and thermal management
The continuous current rating is flat at 250 A from 40 °C through 50 °C. Above that it steps down: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If the panel ambient near the breaker exceeds 50 °C, the actual ampacity is the derated value, not the nameplate 250 A. Maximum power loss is 57 W — that heat has to leave the enclosure, so factor it into the thermal budget for a sealed cabinet.
Breaking capacity by system voltage
The interrupting rating is voltage-dependent: 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. For a 480 V distribution system the relevant value is the 440 V or 500 V figure depending on the actual line-to-line voltage — use the next-higher voltage column if your system falls between the listed points. The 800 V rated insulation voltage gives headroom above the operating voltage for transient overvoltages.
Physical fit and auxiliary switch complement
Dimensions are 105 mm wide, 158 mm high, 70 mm deep. The 105 mm width is a standard 3-pole MCCB footprint for this SENTRON frame size — it occupies three 35 mm DIN modules. The breaker ships with one auxiliary switch and one trip alarm switch (HQ type), so you get a status contact and a separate fault-indication contact without adding an accessory module.