What this choke does on a drive line
The Siemens 4EU3921-0CB00 is a 3-phase commutating choke (line reactor) rated for 650 A continuous at 400 V AC, 50 Hz. It sits between the supply and a converter (VFD or DC drive) to limit current rise during commutation, reduce harmonic distortion, and protect the drive's input diodes from switching transients.
The same choke carries 796.5 A in DC duty, so if you're using it on the DC link side of a 6-pulse rectifier, you get that headroom. The 5.5 % impedance is the key number for coordination: it limits fault current enough to let downstream fuses or breakers clear without the choke saturating. Class H insulation (180 °C thermal class per IEC 60085) means the winding can run hot — total losses are 740 W (530 W coil + 210 W iron core) — so forced air or spacing from other heat sources matters inside the cabinet.
IP00 open-frame construction — no enclosure, so it goes inside a panel or drive cabinet. Dimensions are 0.41 m wide × 0.385 m tall × 0.229 m deep. Main circuit connections use flat-type terminals (bus-bar style), not screw clamps or spring cages. Plan for bolted lugs or bus-bar jumpers. No DIN-rail clip; it bolts to the chassis or sub-panel.