The Schneider Electric C253MG200D is a TM-G thermal-magnetic trip unit for the ComPacT NSX250 DC range, rated 200 A at 40 °C and 750 V DC. It's built for generator protection on DC networks, with three protected poles (3D) and a fixed mounting scheme that wires up clean in a standard panel enclosure.
The 750 V DC rated operational voltage (Ue) is the headline number here — this trip unit handles the higher arc-extinction demands of DC circuits, not just the AC ratings you see on standard TM-D or TM-G breakers. The 200 A rating at 40 °C is the continuous current the trip unit carries without derating; push ambient to 70 °C and you'll need to consult the thermal curve, but the -25 to 70 °C operating range covers most panel interiors. Protection is LI — long-time (thermal) overload with an adjustable Ir pickup from 0.7 to 1 x In, plus fixed instantaneous magnetic short-circuit protection set at 530 A. That fixed Ii means no field tweaking on the magnetic pickup; the 530 A threshold is what it is. The long-time delay tr is also fixed, so the thermal curve shape is preset for generator protection profiles. Compliance with EN/IEC 60947-2 means it's certified for low-voltage switchgear and controlgear — the standard that covers DC circuit-breaker performance, including the short-circuit making and breaking capacity at 750 V DC.
Where this trip unit goes
This is a trip unit for the ComPacT NSX100...250 DC range, meaning it snaps into the breaker chassis — you're not buying a standalone breaker here, just the protection module. The 'Generator' device application tag tells you the thermal and magnetic curves are shaped for generator output protection: slower thermal response to ride through inrush, and a magnetic pickup that clears hard faults without nuisance tripping on generator start-up transients. IP40 protection on the trip unit itself is fine for a closed panel; if the enclosure door is open during maintenance, keep conductive tools away from the terminals. No earth-leakage protection built in — if you need ground-fault on a DC generator feeder, you'll add an external Vigi module or a separate relay.