Klockner‑Moeller NZM104‑400N is a 3‑pole molded‑case circuit breaker rated at 400 A and up to 480 V AC, featuring adjustable long‑time (200–400 A) and instantaneous magnetic trip modules for system protection. Common failure modes include tripping due to overload or short‑circuit conditions, internal coil wear causing loss of trip response, and mechanical wear on the contacts leading to arcing or poor contact resistance. For initial troubleshooting, verify that the breaker is properly seated in its terminal block and that all connections are tight; check the upstream power supply for correct voltage and continuity; inspect the breaker housing and contacts for signs of overheating, corrosion, or physical damage; and review any recorded fault codes or event logs from the control system to confirm whether a trip was due to overload, short, or mechanical fault.[oss-gpt-20b]