The Siemens 4EU3951-0UA00-0A is a three-phase mains choke (line reactor) designed for installation ahead of a frequency converter (variable-frequency drive). It smooths the input current, reduces harmonic distortion, and limits inrush current spikes that would otherwise stress the drive's DC bus capacitors and upstream protection. Inductance is 27 µH (0.0279 mH), sized for the drive's line-side filtering. Total power loss splits between 384 W in the coil and 190 W in the iron core, which must be ventilated — the IP00 open-frame construction means no enclosure, so the choke relies on the panel's airflow to stay within the 40 °C ambient rating.
Physical footprint: 0.41 m wide × 0.385 m tall × 0.229 m deep. This is a substantial component — plan for a dedicated mounting plate or chassis rail in the enclosure; it will not fit a standard DIN rail. Thermal class H insulation (IEC 60085) means the winding can handle a 180 °C hot-spot temperature. In a 40 °C ambient, the 574 W total loss (coil + iron) must be removed by forced or natural convection — do not box it in without calculating the temperature rise. The IP00 rating means it is not protected against dust ingress or accidental contact; install it in a locked or guarded cabinet.