What it is and what it does
The Siemens 3VA2125-6HM42-0AA0 is a 4-pole SENTRON molded case circuit breaker (MCCB) with an electronic ETU330 trip unit, rated 25 A continuously across its full ambient range from 40 °C to 70 °C. That flat derating curve means you don't lose headroom as the panel warms up — a real advantage in a crowded enclosure where a thermal-magnetic breaker would start derating above 40 °C.
Breaking capacity — what those kA numbers mean on your bus
This breaker carries 242 kA at 240 V and 187 kA at 415 V — numbers that put it in the high-interrupting category for an MCCB this size. At 500 V it still holds 121 kA, and at 690 V it drops to 3.7 kA. The practical takeaway for a panel builder: on a 415 V distribution board with a transformer large enough to deliver 187 kA prospective fault current, this one stays coordinated without needing a current-limiting fuse upstream. The 690 V figure is low because the arc energy at that voltage stresses the internal arc chutes; if your circuit runs 690 V with high fault current, you need a different frame.
Integration notes — panel fit and N-wire handling
Dimensions are 140 mm wide, 181 mm high, 86 mm deep — a standard 4-pole MCCB footprint that mounts on a DIN rail or direct panel. The N-conductor protection is adjustable: OFF or 100% of the phase rating, which matters when you're feeding a 3-phase load with a shared neutral that doesn't need overcurrent protection, or a single-phase subfeed that does. Front IP40 keeps out tools and fingers but isn't rated for washdown — this lives inside a dry enclosure.