Incorrectly installed VFDs can result in high levels of interference to other euipment in the same environment. Interference to radio and communications equipment is fairly obvious, but interference to other equipment may be much harder to isolate.
Variable Frequency Drives (VFDs) can cause bearing currents to flow in induction motors and these bearing currents can result in premature failure of these bearings due to EDM (Electrical Discharge Machining).
VFDs are a major source of harmonic currents and if there is a major concentration in a rural area, the resultant harmonic voltages can be very damaging to the supply distribution components and other equipment connected to the supply.
Voltage imbalance can cause major motor failure due to overheating if there is not sufficient de-rating to offset the increased heat losses.