25 A MCCB with ETU350 — what the ratings mean for the panel
The Siemens 3VA2125-6HN36-0AA0 is a SENTRON molded case circuit breaker (MCCB) rated for line protection, carrying a continuous current Iu of 25 A across the full ambient range from 40 °C to 70 °C — no derating needed up to that ceiling. That flat thermal curve is unusual for an MCCB this compact; most competitors start rolling back above 50 °C. The 3-pole frame is paired with an ETU350 electronic trip unit, which gives adjustable overload and short-circuit protection curves rather than fixed thermal-magnetic response. For a panel builder, that means you can dial in selectivity with downstream breakers without swapping the whole device. Breaking capacity is the headline number here: 242 kA at 240 V, 187 kA at 415 V and 440 V, 121 kA at 500 V, and 3.7 kA at 690 V. Those are among the highest interrupting ratings in the 25 A MCCB class — the 242 kA figure at 240 V covers high-fault industrial services where the available short-circuit current is extreme. At 690 V the capacity drops to 3.7 kA, which still handles most motor branch circuits at that voltage level. The rated insulation voltage Ui is 800 V, so the breaker is electrically rated for 690 V systems with margin. Physical footprint: 105 mm wide, 181 mm tall, 86 mm deep. That is the standard 3VA2 frame width — it mounts on a DIN rail or directly to a backplate via the integrated fixing lugs. The front protection class is IP40, meaning tools and fingers are kept out, but it is not sealed against water ingress; keep it inside the enclosure. Power loss is 0.6 W maximum, negligible for thermal budgeting inside a crowded panel.
Integration notes — what the trip unit and options mean
The ETU350 electronic trip unit supports adjustable overload protection (Ir), short-time delay (Isd), and instantaneous (Ii) settings, plus ground-fault alarm or trip if the optional module is fitted — this base version ships without ground-fault monitoring. There is no undervoltage release, no voltage trigger, and no communication function built in, so it is a standalone breaker for line protection. The product extension for a motor drive is listed as optional, meaning the breaker frame accepts a rotary-handle or motor-operated mechanism accessory if remote switching is needed later. No trip indicator on the front; fault indication is through the handle position only.