What this choke does in the circuit
The Siemens 4EU4521-4BA00 is a three-phase commutating choke (line reactor) designed for the converter side of a drive system. Its job is to limit the rate of rise of current during commutation — that means it snubs the diode-recovery spikes and reduces the harmonic content the converter injects back onto the line. Rated for 910 A continuous at 750 V AC, 50/60 Hz, it carries the full converter input current without saturating.
The 910 A continuous rating is the thermal limit at 40 °C ambient; the peak current rating of 1 138 A (125 % of continuous) handles the short-duration overloads common during motor acceleration. Copper losses run 520 W, iron-core losses 404 W — 924 W total heat to vent from the enclosure. Class H insulation (180 °C thermal class per IEC 60085) means the winding can tolerate sustained high temperature without degrading the varnish. The IP00 protection class means it is open-frame — no finger-safe cover, so it must live inside a locked electrical room or an enclosure with a door interlock.
Termination and approvals
Main-circuit connections are screw-type terminals on flat connectors — sized for the 910 A path, so expect large-gauge cable lugs. The choke carries UL/CSA recognition under VDE 0532, which covers the harmonized standard for power reactors. That matters for panel builders who need a cULus mark on the assembly.