What this MCCB is and what it does
The Siemens 3VA1125-4EE42-0AA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels. It carries a 25 A rated current at 40 °C, with the same rating holding through 50 °C — useful when the breaker sits in a warm enclosure without derating. At 55 °C it still delivers 24 A, and at 70 °C it holds 23 A, so the thermal curve stays tight across the operating range. The 4-pole configuration means it switches all three phases plus neutral — standard for three-phase systems where the neutral needs overcurrent protection or disconnection. The TM220 trip unit is a thermal-magnetic design: the thermal element handles overloads, the magnetic element handles short-circuits. No undervoltage release or communication module is fitted, so this is a straightforward standalone breaker for basic feeder protection.
Breaking capacity — what the numbers mean for selectivity
The 3VA1125-4EE42-0AA0 delivers 121 kA at 240 VAC, 75.6 kA at 415 VAC, 52.5 kA at 440 VAC, and 11.9 kA at both 500 VAC and 690 VAC. Those are the maximum fault currents the breaker can safely interrupt at each voltage level. For a site electrical engineer coordinating a panel, the 121 kA figure at 240 V gives headroom for high-fault installations near a large transformer; the 11.9 kA at 690 V is typical for industrial motor circuits at that voltage. The 800 V rated insulation voltage confirms the breaker is built for 690 V systems with margin.
Physical fit and panel integration
The breaker measures 70 mm deep, 101.6 mm wide, and 130 mm high. The 101.6 mm width (4 inches) is the standard footprint for a 4-pole MCCB in a SENTRON panel — it fits the same busbar and mounting pattern as other 4-pole 3VA frames. The IP40 protection on the front means it's protected against tools and wires >1 mm, which is standard for enclosed distribution boards; no washdown rating, so keep it inside the cabinet.