Siemens FD63T125 Molded Case Circuit Breaker Trip Unit

The Siemens FD63T125 Molded Case Circuit Breaker Trip Unit is an interchangeable 3-pole thermal-magnetic trip module designed for FD-frame breakers, delivering 125 A protection up to 600 V AC. As a plug-in trip unit for FD-series frames, it provides long-time (overload) and instantaneous (short-circuit) protection for industrial electrical distribution circuits and is commonly installed in Siemens FD series panels, switchboards, motor control centers, and power distribution panels. It is used for frame upgrades, retrofit work, and replacement of failed or mismatched protective trip modules by maintenance teams, OEM panel builders, and electrical contractors. Common replacements include Siemens FD63T125R (equivalent trip unit) and FD63T125L (complete breaker assembly configuration). The trip unit complies with UL 489 and IEC standards for FD-frame systems.