What this MCCB is and what the ratings mean for fit
The Siemens 3VA1125-5EF36-0DH0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection — meaning it sits at the feeder or branch to protect cables and busbars from overloads and short circuits, not motor or generator duty. It is a 3-pole unit rated 25 A continuous at 40 °C ambient, with a thermal derating curve: still 25 A at 50 °C, then 24 A at 55 °C, 24 A at 60 °C, and 23 A at 65–70 °C. That matters if your panel runs hot — you lose only 2 A at 70 °C, so it holds up well in a crowded enclosure. The interrupting rating is the headline number: 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at 500 V and 690 V. That 187 kA at 240 V means it can safely clear a fault up to that level without rupturing — critical for high-fault-capacity panels like those near large transformers or in industrial distribution. The insulation voltage is rated 800 V, so it's comfortable on 480/277 V or 600 V systems. It includes an undervoltage release (UVR) as the auxiliary release, plus a configurable auxiliary switch block: 2 auxiliary switches + 1 trip alarm switch (HQ). That means you can wire it to drop the breaker if control power fails, and get remote status of the breaker position and trip event — common for safety circuits or remote monitoring in a PLC panel.
Panel fit and mounting
Dimensions: 130 mm height, 76.2 mm width (3 inches), 70 mm depth. That 70 mm depth is shallow enough for most standard distribution panels — it won't hit the gland plate or back wall in a typical 200 mm deep enclosure. The width of 76.2 mm means it occupies three 25 mm pole spaces on a DIN rail or panel-mount footprint. Power loss is 11 W maximum, so thermal rise inside the enclosure is manageable; no forced cooling needed for a single unit.