The Schneider Electric C2544B250 is a MicroLogic 4.2 AB electronic trip unit for the ComPacT NSX100...250 range of molded-case circuit breakers. It is the programmable brain that sits inside the breaker frame, measuring current and deciding when to trip based on the protection curves you set. This is a 4-pole unit (4P) rated at 250 A at 40 °C, designed for AC networks at 50/60 Hz with a rated operational voltage of 440 V AC. The trip unit provides LSoIR protection: L for long-time overload, So for short-time short-circuit with a fixed delay, I for instantaneous short-circuit, and R for earth-leakage. The earth-leakage protection is integrated and Class A, with adjustable sensitivity (IΔn) and time delay (Δt). This makes the unit suitable for special applications requiring both overcurrent and ground-fault protection in a single device.
The long-time pick-up (Ir) is adjustable from 140 to 240 A, so you can fine-tune the overload threshold to match the downstream load without swapping the trip unit. The short-time pick-up (Isd) adjusts from 1.5 to 10 times Ir, giving you selectivity coordination with downstream breakers — a key parameter for panel builders designing a coordinated distribution system per IEC 60947-2. The instantaneous pick-up is fixed at 2880 A — that is the magnetic-only trip level for bolted faults. This matters for motor-starting applications where repeated starts can overheat the circuit.
This trip unit mounts into a ComPacT NSX250 fixed-mount breaker frame. The neutral position is left, and the protected poles can be configured as 3D + N/2, 4D, or 3D — meaning you can set the neutral protection to half the phase current, full current, or none, depending on the system grounding. The local signaling includes a flashing green LED for ready, red LED at 105% Ir for overload, orange at 90% Ir for pre-alarm, and a yellow indicator for residual current. These are visible through the breaker's transparent cover for quick status checks without opening the panel.