What it is and what it does
The Siemens SENTRON 3VA1112-5EF46-0AA0 is a 4-pole molded case circuit breaker (MCCB) rated 125 A at 40 °C, designed for line protection in distribution panels. It carries a TM240 thermal-magnetic overcurrent release — the '240' indicates the fixed thermal trip threshold at 240 A, meaning the breaker's magnetic trip is set to clear short circuits above that level. The interrupting rating hits 187 kA at 240 V, which is well into high-fault-capacity territory for a main or feeder breaker in an industrial service entrance.
Interrupting capacity and derating
At 415 V the interrupting rating drops to 121 kA, at 440 V to 75.6 kA, and at 500 V and 690 V it holds at 17 kA. That's typical for a compact MCCB — the arc extinction gets harder as voltage climbs, so the rating steps down. The continuous current derates from 125 A at 40 °C to 114 A at 70 °C; at 70 °C ambient you lose about 9 % of the rated ampacity. The insulation voltage is rated 800 V, which covers most 480/277 V and 600 V systems with margin.
Panel fit and physical integration
The breaker measures 130 mm high, 101.6 mm wide, and 70 mm deep. The 4-pole width at roughly 100 mm is standard for a 125 A frame — it occupies four module spaces on a DIN rail or panel-mount footprint. Front IP40 protection class means it's protected against tools and solid objects >1 mm, but not sealed against moisture; keep it in a dry indoor enclosure.
Power loss and thermal budget
Maximum power loss is 28.1 W at rated current. That's the heat the breaker dumps into the enclosure at full load. For a panel with multiple breakers ganged together, sum the losses and check the cabinet's dissipation capacity — 28 W per pole group adds up fast in a dense distribution board.