Helps Save Motor Bearings Common-mode current from AC motor controls can damage bearings.
Armored cable can help.
Currents of a few hundred mA can damage motor bearings in a few months. The high-frequency CMC from the speed controller travels through the phase conductors leading to the motor. Armor surrounding the conductors can provide a short, low-impedance return path for these currents. Continuous armor has very good impedance characteristics for this application. As frequencies go up, skin effect makes the impedance of continuous armor drop.