What this MCCB does on your line
The Siemens 3VA1112-6FE42-0AA0 is a 4-pole SENTRON molded case circuit breaker rated 125 A continuous (Iu) with a TM220 thermal-magnetic release. It's built for line protection — meaning it sits upstream protecting feeders and distribution, not a specific motor or drive. The interrupting ratings climb to 220 kA at 240 V and 154 kA at 415 V, so it handles high-fault locations like transformer secondaries or main switchboards without cascading upstream. At 690 V it still clears 17 kA, which covers most industrial service-entrance scenarios. The TM220 release means the thermal element is fixed at 125 A (no amp adjustment), but the magnetic pickup is adjustable up to 1250 A — ten times the continuous rating. That gives you some tuning room for inrush without nuisance trips on transformer energization or capacitor banks. The 4-pole construction handles three-phase plus a switched neutral, common in North American and some IEC distribution panels where the neutral needs overcurrent protection.
Thermal derating — the real-world current
The 125 A rating holds up to 50 °C ambient. Above that it starts dropping: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your panel runs hot — say a non-ventilated enclosure next to a furnace line — you need to size the breaker for the derated number, not the nameplate. The maximum operating temperature is 70 °C, and storage range goes from -40 °C to 80 °C. Power loss at full load is 28.1 W, which matters for thermal calculations in a sealed cabinet.
DIN-rail fit and panel integration
The 3VA1112-6FE42-0AA0 measures 70 mm deep, 101.6 mm wide, and 130 mm tall. That 101.6 mm width is exactly 4 inches — it occupies four standard 1-inch module spaces on a DIN rail, which is what you expect for a 4-pole MCCB in this class. The front face carries an IP40 rating, so it's protected against tools and solid objects larger than 1 mm, but not sealed against moisture. Keep it inside the enclosure; don't mount it on a weather-exposed panel door.
DC capability and special notes
The maximum rated operational voltage for DC is 600 V. The manufacturer's manual covers DC switching values separately — the short-circuit protection design note references the 3VA molded case circuit breaker device manual for DC network applications. The N-conductor protection is set at 50%, meaning the neutral pole trips at half the phase rating, which is standard for 4-pole breakers where the neutral isn't expected to carry full phase current continuously.