What it is and what it does
The Siemens 3VM1125-4ED42-0AA0 is a 4-pole IEC circuit breaker on the 3VM1 frame, rated 25 A with a TM210 thermal-magnetic trip unit. The 36 kA breaking capacity at 415 V (class S) means it can safely interrupt fault currents up to that level on a 400 V distribution bus — enough for most commercial and light industrial panelboards without needing an upstream current-limiting fuse. Overload protection is fixed at Ir = 25 A; short-circuit pickup is set at 12.8 × In (320 A), non-adjustable. The neutral conductor is unprotected, so this breaker goes on a 3-phase + solid neutral system where the neutral is not switched or monitored.
Panel integration notes
Mounts on a standard DIN rail — the 150 × 119 × 116 mm envelope fits a typical 160 A frame footprint. The nut keeper kit is included, which saves a trip to the hardware drawer when securing the busbar connections. No neutral conductor protection means the installer runs a solid neutral bar through the breaker without a pole; verify the downstream neutral bus is rated for the full fault current.