MCCB with ETU550 — interrupting capacity and thermal derating
The Siemens SENTRON 3VA2125-7JP32-0FD0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection with a continuous current Iu of 25 A. Its interrupting capacity is 330 kA at 240 V and 242 kA at 415 V — these numbers cover high-fault scenarios at the service entrance or downstream of a large transformer, where available fault current can exceed 200 kA. At 690 V the rating drops to 3.75 kA, so this breaker is not intended for 690 V line-side protection without coordination study. The electronic trip unit is an ETU550, which provides adjustable long-time, short-time, instantaneous, and ground-fault protection curves. The breaker carries three auxiliary switches (HQ) for remote status indication, plus an undervoltage release with leading NO contacts — the leading contact arrangement means the UVR signals its own state before the breaker opens, useful in safety circuits that need to confirm the release is reset before reclosure.
Thermal derating — what the 25 A rating actually means in a warm panel
The 25 A rating holds at ambient temperatures up to 50 °C. At 55 °C it derates to 24.1 A, at 60 °C to 23.1 A, and at 70 °C to 21.25 A. In a sealed enclosure with other heat sources, the real continuous current the breaker can carry without nuisance tripping is the derated value at the panel internal temperature — not the nameplate 25 A. Plan for the ambient inside the enclosure, not the control-room temperature.
Integration — dimensions, auxiliary components, and panel fit
The breaker measures 105 mm wide, 181 mm high, and 107 mm deep — a standard 3-pole MCCB footprint for DIN-rail or screw-mount panel installation. The supplied basic switch is order code 3VA2125-7JP32-0AA0; the integrated auxiliary trip is 3VA9908-0BC24. These are the factory-matched accessories for this breaker variant — order them alongside if the panel build requires the UVR or auxiliary switch to be pre-installed.