Voltage ratings for VFD cable

Why Cable Choice Matters in VFD Systems

Not all cables are created equal, especially when it comes to Variable Frequency Drives (VFDs). Using the wrong cable can lead to serious problems, including equipment failure and safety risks. That’s why I’m starting this series on VFD wiring best practices. Today, let’s look at why VFDs are different from standard motor connections and why cable selection is so important.

What Makes VFDs Different?

A standard motor drive simply passes through the incoming power. A VFD, however, changes power twice:

• First, it converts AC (alternating current) to DC (direct current).

• Then, it converts DC back to AC at a controlled frequency.

This process introduces electrical distortions that can stress your cables if they’re not designed for VFD use.

Why Voltage Matters

Inside every VFD is a “DC Bus” that stores energy. The voltage here is higher than you might expect (VDC ≈ VAC Input x 1.414):

• For a 480V input, the DC Bus is about 678V.

• For a 230V input, it’s about 325V.

This means the cables you choose must handle these higher voltages safely. In North America, 230V and 480V systems are common, while in Europe, 230V and 380V systems are typical, so always check the cable’s voltage rating especially when using a European cable. In long cable runs it is possible to see even higher voltage spikes due to the reflected wave phenomena.

Best practice tips:

• Always use shielded cables with XLPE insulation. Type XHHW-2 is good, type RHW-2 is better due its lower capacitance.

• Only use cable with at least 1000V rating with listing type “Flexible Motor Supply”. Some is dual rated “600V TC” and “Flexible Motor Supply” (aka Flexible VFD & Servo)

• Terminate the cable shield on both ends. Use a shield clamp on the drive end, and a 360° EMC gland on the other end.