The C16B3TM125 is a 3-pole ComPacT NSX moulded-case circuit breaker from the Schneider Electric NSX160B range, fitted with a TM-D thermal-magnetic trip unit rated 125 A at 40 °C.
Breaking capacity — the number that decides fit
At 415 V AC (the common European and UK distribution voltage), this breaker delivers 25 kA Icu per IEC 60947-2. That's the B breaking capacity code — enough for most secondary distribution panels downstream of a transformer. At 240 V AC it hits 40 kA Icu, and at 500 V AC it still holds 15 kA Icu. The utilisation category is A (no intentional short-time delay), so it's a straightforward feeder or branch breaker, not a main that needs selective coordination with downstream devices.
The 105 mm width and 161 mm height are standard for the NSX160B frame; depth is 86 mm including the toggle handle. Front connections top and bottom, 35 mm connection pitch. IP40 enclosure protection keeps dust out of a clean indoor panel; IK07 impact rating means it can take a knock from a dropped tool during commissioning.