How and Why to Properly Terminate your VFD Cable

While it is acceptable to terminate the phase conductors of a VFD cable as you would any other industrial power cable, special attention needs to be paid to the termination of the cable shield.  The shield is an important part of the VFD cable but if it is not terminated properly, most of the benefits that this shield provides are negated.  If you don’t properly terminate a VFD cable’s shield you may as well have not spent the extra money on VFD cable to begin with!

Proper shield termination allows the shield to become a low impedance path for high frequency common mode current to flow from the motor back to the inverter.  Without this controlled path, these currents can travel through motor bearings and building infrastructure and cause problems with other sensitive equipment like PLCs, control, and communication systems located throughout your facility.

There are three main types of shield found in VFD cables and Southwire makes VFD cables with each of these shield types.  The shield types are: copper braid shield with aluminum foil (Copper Braid); A helically applied copper tape (Copper Tape); and a continuously corrugated welded
aluminum used in MC cables (Aluminum Welded Armor).   This application note will detail how to terminate each of these shield types.

VFD TERMINATION KITS - APPLICATIONS AND FEATURES:

Southwire’s Variable Frequency Drive (VFD) Shield Termination Kit provides the means to properly terminate a VFD cable’s overall shield. The kit can be used on Southwire’s copper tape shield VFD cables and copper braid/aluminum foil shield VFD cables. Drive manufacturers stress the importance of proper shield termination as it helps prevent premature motor failure due to bearing fluting as well as intermittent operational issues associated with communication and control equipment located in close proximity to uncontrolled common mode ground currents. The termination kit provides a low impedance path at high frequency for common mode current created by the drive to return to the inverter via the shield and minimizes potential problems.

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