What this MCCB carries and where it fits
The Siemens SENTRON 3VA1112-6EF36-0BH0 is a 3-pole molded case circuit breaker (MCCB) rated 125 A continuous at 40 °C, with a full-rated current that holds flat through 50 °C before a gentle derating curve kicks in — 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. That means it carries its nameplate rating in most ventilated enclosures without a derate penalty. Breaking capacity is 220 kA at 240 V, 154 kA at 415 V, 75.6 kA at 440 V, and 17 kA at both 500 V and 690 V. For a 125 A frame, that's high-interrupting capability — it handles bolted faults on high-capacity transformers without cascading upstream. This is a line-protection design (not motor-protection pattern), so the thermal-magnetic trip curve is set for cable and busbar protection. It includes an undervoltage release (UVR) as standard, plus two auxiliary switches and one trip alarm switch (HQ) — that's enough status feedback for a remote PLC input without an add-on module. Insulation voltage is rated 800 V, and the maximum power loss at rated load is 30.6 W — a number to check against your enclosure thermal budget if you're packing several breakers in a row.
Panel fit and mounting
Footprint is 76.2 mm wide (3 in), 130 mm tall (5.12 in), 70 mm deep (2.76 in). That's a standard SENTRON 3VA frame width for a 3-pole 125 A unit — it clips onto the mounting plate or DIN rail adapter without stealing extra width from adjacent breakers. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The 70 °C operating ceiling matches the derating table endpoint, so the breaker can live in a warm panel as long as you respect the derate.