The C254TM160 is a TM-D thermal-magnetic trip unit for the ComPacT NSX250 range, rated 160 A at 40 °C with 4 poles configured as 4D (neutral fully protected). It provides LI protection — L for overload (thermal) and I for short-circuit (magnetic) — per EN/IEC 60947-2. The instantaneous magnetic pickup is fixed at 1250 A, and the long-time thermal pickup is adjustable from 0.7 to 1.0 × In.
If your panel runs hotter — say 50 °C — you'll need to derate or step up to the next frame. The 1250 A instantaneous pickup means the magnetic element clears a short-circuit fault the moment current exceeds roughly 7.8× In; that's a fixed threshold, so it's not adjustable in the field. The long-time thermal curve has a fixed delay of 120–400 s at 1.5× In and 15 s at 6× Ir, which coordinates with typical downstream branch breakers on a distribution panel.
This trip unit snaps into a ComPacT NSX250 fixed-mount circuit breaker frame — the 4D pole configuration means the neutral pole is fully protected (same trip curve as the phases), which is required for four-wire distribution systems where the neutral carries load current.