What this MCCB is and what it does
The Siemens SENTRON 3VA1225-5FF42-0AE0 is a 4-pole molded case circuit breaker (MCCB) rated for 125 A continuous current, designed for line protection in distribution panels. It carries a TM240 thermal-magnetic overcurrent release — the thermal element handles overloads, the magnetic element clears short-circuits. Breaking capacity sits at 187 kA at 240 V AC, tapering to 121 kA at 415 V, 75.6 kA at 440 V, 30 kA at 500 V, and 17 kA at 690 V — so it can interrupt high-fault currents without cascading upstream, even on 480 V industrial services where the 75.6 kA figure applies. Insulation voltage is rated 800 V, giving headroom for 690 V line-to-line systems. The 125 A rating is fixed — not adjustable — so this breaker is sized for a specific load or feeder, not for field tweaking. The 4-pole configuration (three phases plus neutral) suits three-phase four-wire systems where the neutral needs overcurrent protection. Power loss at full load is 57 W, which matters for panel thermal budgeting if you're packing several breakers in a closed enclosure.
Mounting and panel fit
Dimensions are 158 mm high, 140 mm wide, 70 mm deep — a standard MCCB footprint for this current class. The 140 mm width (5.51 in) is the critical dimension for multi-breaker rows: it determines how many fit across a panel. Depth of 70 mm (2.76 in) is shallow enough for most 200 mm deep enclosures, leaving room for wiring gutters. Operating temperature range is -25 °C to 70 °C, storage from -40 °C to 80 °C, so it handles unheated outdoor cabinets as long as the ambient stays above -25 °C.