Evaluating Critical VFD Cable Parameters

Brandon L. Phillips Eric J. Bulington
Product Development Engineer Northeast Industrial Account Manager
VFDs (Variable Frequency Drives) seem to be ever present in applications ranging from motion control to commercial flow/pumping. VFDs, also known as Adjustable Speed Drives or Variable Speed Drives require special considerations for the proper installation and operation of the drive system as well as the proper operation of nearby or adjacent systems. The nature of their operation impacts both longevity and reliability of these systems. This paper examines the motor-supply cable's impact on VFDs and surrounding equipment. Included are some fundamental guidelines for their installation and design.
Evaluation of Cable Types Used for VFDs
In order to provide an understanding of the variables and a guide in cable selection, the most commonly recommended cables for VFD applications were studied in both a lab and working application. Some wiring methods were not examined, such as THHN building wire in conduit, as their use has been shown to have detrimental effects, as outlined in other studies.1 2 The exception to this was the use of PVC-Nylon insulated, PVC jacketed, tray cables. These cables are the most commonly installed industrial control cable and are often misapplied for use in VFD applications. For this purpose they are included for comparison. The PVC-Nylon designs were evaluated in both unshielded and foil shielded versions with their photos included below. Other cables evaluated were:

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