What it is and what it does
The Siemens SENTRON 3VA1112-5EF42-0AA0 is a 4-pole molded case circuit breaker (MCCB) built for line protection. It carries a TM240 thermal-magnetic release — the thermal element handles overloads, the magnetic element handles short-circuits. Rated at 125 A continuous at 40 °C, it's meant for a main feeder or a large downstream branch in a distribution panel.
How the ratings matter on the route
The interrupting capacity is the number that tells you whether this breaker will clear a fault without welding its contacts or blowing apart. At 240 V it's rated 187 kA — that's a very high figure, typical for a main breaker close to a transformer. At 415 V it's still 121 kA, at 440 V it's 75.6 kA, and at 500 V and 690 V it drops to 17 kA. The available fault current at your panel's secondary voltage has to be below these numbers, or the breaker won't safely interrupt a bolted fault. The continuous current rating is temperature-dependent. At 40 °C, 45 °C, and 50 °C it's a full 125 A. At 55 °C it derates to 122 A, at 60 °C to 120 A, at 65 °C to 117 A, and at 70 °C to 114 A. If this breaker lives in a hot panel — say near a drive or a transformer — you need to size the load for the derated figure, not the 125 A nameplate. The insulation voltage is rated 800 V, so the internal clearances and creepage are designed for 800 V class systems. Power loss at full load is 28.1 W — that's heat that has to be vented out of the enclosure. The front face carries an IP40 protection class, meaning it's protected against tools and wires over 1 mm but not against water. No trip indicator, no undervoltage release, no ground-fault monitoring on this variant.
Panel fit and dimensions
The breaker is 70 mm deep, 101.6 mm wide, and 130 mm tall. That width — 4 inches — is a standard MCCB footprint for a 4-pole 125 A frame. It bolts into a panel on a mounting plate or a DIN rail adapter (the SENTRON 3VA series uses a common mounting base). The depth matters for enclosure depth selection: 70 mm plus wire bending space and the handle clearance means a 200 mm deep enclosure is tight; 300 mm is comfortable.