When adding a variable-speed system to your industrial design, variable frequency drives (VFD) or motors are often a wise choice to provide speed and torque control thanks to their efficiency and precision. However, specifying the right cable for a VFD application is not always easy. Selecting the right cable requires careful attention to factors like cable construction for harsh conditions and mitigating system noise. In addition, it’s also important to follow the guidance of VFD drive and motor manufacturers as well as from companies that specialize in high-quality VFD cables. This blog post will provide an overview of some important considerations to remember as you create an optimal cable connection between your drive and motor.

Amps and Horsepower Determine AWG Size

In order to determine your VFD cable’s wire gauge, consult your cable manufacturer’s or motor manufacturer’s AWG chart. For example, SAB’s VFD Motor Properties Chart — covering 230- and 575-V motors — will suggest an appropriate AWG to use based on your motor’s amps and horsepower. The amps in SAB’s table are based on NEC Art. 430.250, and full load current (FLC) is calculated by multiplying the amps by 1.25. You can find selection charts for SAB cables from leading manufacturers like ABB, Allen Bradley, GE, Mutsubishi, Siemens, SquareD and Yaskawa. Note that the cable voltage should meet or exceed that of the VFD.

Remember the Grounding Gland

VFD systems may produce high common-mode currents due to unbalanced three-phase vector sums that prevent the current from equalling zero at neutral. As part of your VFD selection process, it’s important to provide a grounding path at the enclosure and motor housing. SAB EMC strain relief glands feature built-in grounding mechanisms that come in contact with a cable shield, creating a ground path to earth for complete protection against unwanted EMC noise. In fact, they can even eliminate the need for drain wire. ​​EMC-2 is desirable for use in corrosive conditions, and the EMC-4 allows for free radial and axial cable movement that doesn’t harm the braid.

Look for a Large Cable Selection

Because VFDs are often found in various challenging applications and harsh environments, your cable’s construction should be appropriate for its intended operating conditions. That’s why it’s important to work with a manufacturer that offers a large selection of cables designed to accommodate a wide range of applications and stand up to extreme conditions that could compromise performance and lifetimes. These conditions include continuous flexing, oil and chemical exposure, sunlight, extreme temperatures and more.

At SAB, our expansive lineup of VFD cables can satisfy most any VFD need. Our cables are constructed with thick cross-linked polyethylene (XLPE) insulation that provides exceptional heat resistance and lower capacitance while minimizing charging currents — characteristics where PVC insulation may fall short. They also carry RHW-2 and XHHW-2 ratings, and they are compliant with the NFPA 79, 2018 Edition. The family includes double-shielded versions for effective CMC protection, UL TC-ER and UL WTTC ratings, as well as sunlight-, oil- and chemical-resistant cables. Symmetrical types are also available. Our VFD cable highlights include:

• VFD XLPE TR/VFD XLPE TR D. This Type TC-ER-rated flexible VFD cable resists oil and sunlight, is available with drain wire and carries direct burial approval.
• VFD XLPE TR Lean. Featuring a reduced outer diameter with double shield, this 1,000-V TC-ER flexible VFD cable comes with a black PVC jacket that resists sunlight and oil.
• VFD Combo XLPE. Our VFD Combo consists of a shielded pair for temperature sensor or brake and features Oil Res 1 & 2 compliance, sunlight resistance and direct burial approval.
• VFD XLPE Auto TR. This TC-ER rated continuous flex and oil-resistant VFD cable comes with XLPE insulation plus shielded pair construction.
• VFD Symmetrical XLPE-TR. Our flexible VFD cable includes three symmetrical grounds and a shielded pair for a sensor or brake.

Our wide range of robust, reliable VFD cable products give you the flexibility you need to achieve optimal VFD connections that withstand tough conditions over a long operating lifetime.

For more information about SAB VFD cables and EMC Grounding glands, visit our Motors & Drive's Application Page.