What this MCCB brings to the panel
The Siemens SENTRON 3VM1108-5MG32-0AA0 is a 3-pole molded case circuit breaker rated for 128 A maximum with a TM110M thermal-magnetic release — the thermal element handles overloads, the magnetic element catches short-circuit events. The interrupting ratings are what make this part interesting: 187 kA at 240 V AC, 121 kA at 415 V, 75 kA at 440 V, and 17 kA at 500 V. That 187 kA figure at 240 V means it can safely clear a fault on a high-capacity transformer secondary without the upstream breaker needing to coordinate — useful in a main or feeder position where fault current is stiff. The 800 V rated insulation voltage tells you the internal clearances are built for 480/600 V class systems, not just 240 V residential. Thermal derating is on the datasheet and it matters for panel fill: at 40 °C it carries the full 8 A continuous, but at 55 °C it's down to 7.76 A, and at 70 °C it's 7 A (–). If this breaker lives in a hot enclosure next to drives or transformers, that derating curve is the one that governs the real load it can hold — not the 128 A maximum. The 2 W maximum power loss is low enough that it won't drive internal cabinet temperature up by itself.
Panel fit and dimensions
The breaker measures 76.2 mm wide, 130 mm tall, and 70 mm deep (–). That 76.2 mm width is three inches — it fits a standard 3-pole MCCB footprint on DIN rail or a panel-mount base. The IP40 protection on the front means it's protected against tools and wires >1 mm, but it's not sealed against water — keep it inside the enclosure, not on the door. No undervoltage release, no ground-fault monitoring, no communication function on this variant — it's a straight thermal-magnetic breaker with no auxiliary electronics, so wiring is just line in, load out.