What the ratings mean for fit
The Siemens 3VM1125-3ED42-0AA0 is a SENTRON molded case circuit breaker (MCCB) in the 3VM platform, sized for line protection in distribution panels. Four poles cover three-phase-plus-neutral or dual-fed configurations. The TM210 thermal-magnetic release gives fixed thermal and magnetic trip points — no adjustment dial, so the breaker is set at the factory for the 25 A continuous rating at 40 °C. That continuous rating holds flat through 50 °C, then derates to 24 A at 55 °C and 23 A at 70 °C (–). If the panel ambient runs hot, size the load side accordingly. Interrupting capacity is the headline number here: 76 kA at 240 V AC, 53 kA at 415 V, 32 kA at 440 V, and 12 kA at 500 V. That 76 kA at 240 V means this breaker can safely clear a fault on a high-capacity 240 V distribution bus without upstream fuses needing to coordinate — useful for transformer-fed subpanels or industrial lighting panels where available fault current is high. At 415 V, the 53 kA still covers most industrial motor-control center (MCC) applications. The 12 kA at 500 V is the floor; verify against your utility's worst-case fault study. Rated insulation voltage Ui is 800 V, and maximum operating voltage is 690 V AC with a DC rating of 500 V. That gives headroom for 480 V and 600 V class systems. The front IP40 means it's protected against tools and wires >1 mm — standard for enclosed panel mounting, not for washdown zones.
Footprint and panel integration
Dimensions are 70 mm deep, 101.6 mm wide, 130 mm high (–). That 101.6 mm (4-inch) width for a 4-pole MCCB is compact — fits standard 4-inch gutter space in a 600 mm wide enclosure. Depth at 70 mm leaves room for rear bus connections without crowding the backplane. No undervoltage release, no communication module, no ground-fault monitoring — this is a bare breaker; any accessories add to the depth or width. Verify the mounting base accepts the standard SENTRON plug-in or fixed lugs before panel layout.
Thermal performance across temperature
The breaker carries a maximum power loss of 9 W at rated load. Operating temperature range is -25 °C to +70 °C; storage range is -40 °C to +80 °C. The derating curve above 50 °C is gradual — only 1 A drop per 5 °C step — so it's usable in moderately warm enclosures without oversizing. No trip indicator means you won't get a visual flag on the handle; rely on the position indicator only.