The C25B42D250 is a 4-pole ComPacT NSX250B moulded-case circuit breaker rated 250 A at 40 °C, with a MicroLogic 2.2 electronic trip unit providing L (long-time overload), So (short-time short-circuit with fixed delay), and I (instantaneous short-circuit) protection curves. The 40 kA Icu at 240 V AC drops to 25 kA at 415 V AC and 15 kA at 500 V AC — the 415 V figure is the one that governs most European distribution panels, and the 500 V figure matters if you are feeding a step-up transformer or a 480 V motor control centre. This breaker is built for distribution duty (Category A utilisation), not motor-starting across-the-line — use it for feeder protection, bus couplers, or branch circuits where the load is resistive or mixed. The 4-pole version with neutral left suits TT or IT earthing systems where the neutral needs switching.
Compliance documentation is standard for the ComPacT NSX family: the breaker is designed to EN/IEC 60947-2, carries the CE mark for the European market, and is UL/CSA listed for North American installations — the 40 kA Icu at 240 V AC is the UL 489 interrupting rating, while the 25 kA at 415 V AC is the IEC 60947-2 rating. RoHS and REACH declarations are available from the manufacturer's documentation portal.
Mounts on a backplate with the 35 mm pitch connection spacing standard for the NSX frame. The 140 mm width × 161 mm height × 86 mm depth footprint fits a standard distribution section; the front-front connection (both line and load terminals on the front face) simplifies busbar routing and allows the breaker to sit flush against the backplate without rear-access clearance. The toggle control and the local LED signalling — green for ready, red at 105 % Ir overload, orange at 90 % Ir pre-alarm — give the commissioning engineer a visual status without opening the panel door. Five accessory slots on the front face accept shunt trips, auxiliary contacts, undervoltage releases, or motor operators — wire them in before the breaker goes into the panel to avoid rework. The IP40 front face and IK07 impact resistance mean the breaker survives the panel-build stage without a protective cover, but the IP rating is not washdown-rated; keep it behind a gland plate in wet areas.