The C164MG125D is a TM-G thermal-magnetic trip unit for the ComPacT NSX160 DC range, rated 125 A at 40 °C and built for 4-pole DC generator protection. It is a fixed-mount trip unit with LI protection — long-time (thermal) overload and fixed instantaneous magnetic short-circuit pickup at 530 A. The long-time pickup is adjustable from 0.7 to 1 x In, so you can dial the overload threshold to match the generator's continuous current without swapping the trip unit.
Rated operational voltage is 750 V DC — this is the maximum DC bus voltage the trip unit can interrupt under fault. For a 125 A generator circuit on a 750 V DC bus, the TM-G's fixed instantaneous pickup at 530 A means it will clear a short-circuit without waiting for thermal delay, which is what you want for semiconductor protection in DC drives or battery banks. The 4D protected poles indicate all four poles switch the DC line; no neutral pole is left unprotected. IP40 enclosure keeps out tools and small wires but not moisture, so mount inside a weatherproof cabinet if the panel sees washdown or outdoor exposure.