Line reactor for drive input harmonics
The Siemens 4EU3951-6UA00-0A is a three-phase mains choke (line reactor) rated for 710 A AC maximum current at 400/480 V AC, 50/60 Hz. It sits between the supply and a frequency converter to limit harmonic distortion, reduce voltage notching, and protect the drive DC bus from line transients. Total power loss runs 730 W (540 W coil + 190 W iron core) at 40 °C ambient, thermal class H insulation per IEC 60085. That means the winding can sustain 180 °C hot-spot temperature — adequate for continuous duty inside a ventilated cabinet. The IP00 open-frame construction requires the panel builder to provide finger-safe clearance or a separate enclosure; this is not a stand-alone device. Main circuit connection uses flat-type terminals. The 0.229 m depth, 0.41 m width, and 0.385 m height require a dedicated mounting plate.
The 639 A operational current (I LN) is the rated continuous current at the nominal 4% voltage drop; if your drive draws 639 A or less, the reactor stays within its design impedance. Above that, the voltage drop climbs and the core may saturate earlier. The 4% relative inductive voltage drop (Uk) at rated current is a standard value for drive input reactors. It provides enough impedance to attenuate the 5th and 7th harmonics that dominate a 6-pulse rectifier input, without dropping so much voltage that the DC bus undervolts during heavy load. If your application requires tighter harmonic control (IEEE 519 compliance), you may need a higher-impedance reactor or a multi-pulse drive — but for most industrial VFD installations, 4% is the sweet spot.