The Siemens 4EM5008-0DK00 is a single-phase commutating choke (line reactor) designed for converter front-ends. It limits current rise during switching events, reducing harmonic distortion and protecting the DC link from line notches. Rated for 690 V AC at 60 Hz, it carries 20 A maximum AC current and delivers 2.2 mH inductance with a 2.4% relative inductive voltage drop at rated load. That 2.4% drop is the key sizing figure — it tells you the choke is matched to the converter's impedance budget, so swapping in a different value shifts the voltage sag and can trip the drive on undervoltage.
This choke is IP00 — no enclosure, no finger-safe cover. It mounts inside a panel, typically on a base plate or DIN rail via an optional bracket (not included). Dimensions are 0.115 m deep, 0.097 m wide, 0.111 m tall, so it fits in a standard 200 mm deep enclosure with room for gland plates and wiring ducts. Terminals are screw-type or tab connections, accepting solid or stranded copper up to the rated current. The thermal class B (130 °C) insulation system means the winding can run hot without degrading — fine for a 40 °C ambient, but if your panel ambient pushes past that, derate the continuous current or add forced ventilation.
The 20 A maximum AC current is the thermal limit (Ith) — the choke can carry that continuously in free air at 40 °C. The 18 A rated operational current (I_LN) is the design point for the 2.4% voltage drop; running at 20 A pushes the drop higher and increases core saturation, so the 18 A figure is the one to use for sizing against your converter's nominal input current. Power loss splits into 14.3 W in the winding (copper) and 25.8 W in the iron core — total 40.1 W dissipated as heat inside the panel.