What this MCCB is and what it handles
The Siemens SENTRON 3VA1225-4GF42-0BH0 is a 4-pole molded case circuit breaker (MCCB) rated for 250 A continuous current (Iu) with a TM240 thermal-magnetic overcurrent release, set up for line protection out of the box. It carries a 121 kA breaking capacity at 240 V, 75.6 kA at 415 V, and 25 kA at 440 V — numbers that tell you it can sit upstream of a big distribution panel or a motor control center and still hold coordination with downstream breakers. The 800 V rated insulation voltage (Ui) covers most industrial line-to-line voltages you'll see in a plant. The TM240 release is a fixed thermal-magnetic type — no interchangeable trip units, so what you see is what you get for overload and short-circuit protection. That matters for a procurement decision: if your BOM calls for a 250 A frame with a 240 A thermal pickup, this is a direct fit. The 4-pole construction handles three-phase plus neutral, with 100% N-conductor protection rated.
Breaking capacity — what the ratings mean for coordination
Breaking capacity is the fault current this MCCB can safely interrupt without welding contacts or venting gas into the panel. At 240 V it's rated 121 kA; at 415 V it drops to 75.6 kA; at 440 V it's 25 kA; at 690 V it's 11.9 kA. These are symmetrical RMS values. For a site electrical engineer working selectivity, the 415 V figure is the one that governs in a 400 V distribution board — 75.6 kA is enough to sit behind a transformer without needing a current-limiting fuse upstream in most installations.
Thermal derating — what the ambient temperature curve tells you
The 250 A rating holds flat from 40 °C through 50 °C ambient. At 55 °C it derates to 243.3 A, at 60 °C to 236.5 A, at 65 °C to 229 A, and at 70 °C to 223 A. That's a gentle slope — about 1% per 5 °C above 50 °C. For a panel OEM wireman packing breakers into a closed cabinet, this means you can run it at full 250 A in a ventilated 50 °C enclosure without oversizing the frame. In a hot pump house or near a furnace, you'll need to account for the derate or bump up to the next frame.
Physical fit and auxiliary wiring
Dimensions are 158 mm high, 140 mm wide, 70 mm deep — a compact 4-pole footprint that fits standard Siemens 3VA panel cutouts and busbar systems. The front face carries IP40 protection, meaning tools and fingers stay out but no water ingress protection; keep it inside a panel or enclosure. It ships with an undervoltage release (UVR) and a 2-auxiliary-switch-plus-1-trip-alarm-switch HQ auxiliary contact block. The UVR is the coil-style release that trips the breaker when control voltage drops — common for emergency-stop circuits and undervoltage protection schemes. The auxiliary contacts provide status feedback for PLC inputs or remote indication.