The C4034A400 is a Schneider Electric MicroLogic 4.3 AL electronic trip unit for the ComPacT NSX400...630 molded-case circuit breaker platform. It is rated 400 A at 40 °C, 3-pole with 3D protected poles, and carries LSoI protection functions — long-time (L), short-time short-circuit with fixed delay (So), and instantaneous (I) — plus integrated earth-leakage protection Class A. Built to EN/IEC 60947-2, this trip unit is the brain of the breaker: it measures current through the integral current transformers and decides when to signal the breaker to open. The long-time pick-up Ir is adjustable from 160 to 400 A across nine settings, letting you match the cable or busbar ampacity without swapping the trip unit. The short-time pickup Isd adjusts from 1.5 to 10 x Ir, and the instantaneous pickup Ii is fixed at 4800 A — that is the hard floor for clearing a bolted fault. Earth-leakage sensitivity IΔn and time delay Δt are both adjustable, with delay options from 0 ms to 1 s for coordinating downstream with RCDs or upstream with a main breaker.
Protection curve and selectivity
The fixed long-time delay tr gives 11 s at 7.2 x Ir, 16 s at 6 x Ir, and 400 s at 1.5 x Ir — these are the curves that govern motor start and transformer inrush ride-through. Zone selective interlocking (ZSI) is not fitted on this unit, so selectivity with downstream breakers relies on time-current curve grading alone. For a panel where ZSI is required for faster fault clearing, the MicroLogic 5.3 or 6.3 series with ZSI option would be the next step up.
Integration notes
This trip unit snaps into the ComPacT NSX400...630 fixed breaker. It is IP40 rated (IEC 60529), so it is suited for panel interiors where the enclosure door provides the environmental seal. The local signalling panel shows a flashing green LED for ready, red LED at 105 % Ir for overload, orange LED at 90 % Ir for pre-alarm, and a yellow indicator for residual current. Earth-leakage protection can be disabled via the IΔn rotary switch — useful during commissioning or when feeding a transformer that has its own earth fault protection.