What the 121 kA interrupting rating means for your panel
The Siemens SENTRON 3VA1125-4EF32-0DC0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection, carrying a continuous current Iu of 25 A. Its interrupting capacity reaches 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at 690 V — that SCCR headroom means it can safely clear a bolted fault on a high-capacity transformer secondary without upstream fuses having to open first. The thermal-magnetic release is a TM240, so the thermal curve is fixed and non-interchangeable; the magnetic pickup is factory-set to the 240 A range. This is a fixed-thermal, non-communicating breaker — no trip indicator, no phase-failure detection, no communication module. It does carry an undervoltage release (UVR) as the auxiliary release, and the auxiliary contact version is 2 auxiliary switches HQ, which gives you two form-C contacts for status feedback to a PLC or annunciator.
Thermal derating and ambient temperature profile
The 3VA1125-4EF32-0DC0 holds its full 25 A rating up to 50 °C ambient. Above that, it derates linearly: 24 A at 55 °C, 23.5 A at 60 °C, 23 A at 65 °C, and 22.5 A at 70 °C. That's a 10 % reduction from 25 A to 22.5 A across the 50–70 °C band — tight enough that a panel designer can size for 25 A and still have margin at the high end of a NEMA 12 enclosure. The operating range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The front face carries IP40 protection, so it's splash-safe from the front but not sealed against hose-down — mount it inside a panel rated for the environment.
Physical fit and panel integration
The 3VA1125-4EF32-0DC0 measures 70 mm deep, 76.2 mm wide, and 130 mm high. That width is a standard 3-pole MCCB footprint — it drops into a panel cutout or DIN-rail adapter designed for the SENTRON 3VA frame. The undervoltage release and the two auxiliary switches (HQ) add depth behind the breaker; verify clearance for the wiring of those terminals. The integrated auxiliary trip order code is 3VA9608-0BB25 if you need a replacement coil or release module.
Coordination and selectivity notes
Because the TM240 release has a fixed thermal curve, selectivity with downstream miniature circuit breakers (MCBs) depends on the MCB's instantaneous trip threshold. The 3VA1125's magnetic pickup is at 240 A (10x Iu), so a downstream 16 A MCB with a B-curve (instantaneous at 3–5x In) will trip before the MCCB on a low-level fault. For full selectivity up to the MCCB's instantaneous threshold, pair it with a downstream breaker whose let-through energy (I²t) is below the MCCB's magnetic trip level. The 15 000 latching endurance cycles mean it's rated for infrequent switching — it's a protection device, not a load-break switch.