The VFD power cable is only as effective as its shielding and termination. No matter how well-designed the cable itself, improper shield installation or termination can increase EMI emissions and common-mode current, raising the risk of interference, bearing-current damage, and premature motor failure. In VFD systems, the shield is not an optional accessory—it is a functional component that must be engineered and installed with the same care as the phase conductors.
PWM drives can produce steep-front voltage pulses with sub-microsecond rise times, depending on the drive design and operating conditions. These fast transients create high-frequency common-mode currents that seek a low-impedance return path. Without a continuous, low-impedance shield bonded correctly at both ends, more of this current may flow through unintended paths, including motor bearings, increasing the risk of electrical discharge machining (EDM), pitting, and premature bearing failure.
Why Does a VFD Power Cable Need Shielding?
Electrical Noise Generated by VFD Systems
PWM inverters output high-frequency voltage pulses with extremely fast rise times. These pulses generate:
- Radiated EMI: The cable acts as an antenna, radiating electromagnetic interference that can disrupt nearby instrumentation, sensors, and communication systems
- Conducted EMI: High-frequency noise travels back through the power distribution system
- Common-mode currents: High-frequency currents that flow through motor bearings to ground
- Shaft voltages: Voltages induced on the motor shaft that discharge through bearings
The Two Core Functions of Shielding
EMI Suppression
The shield contains the electromagnetic field generated by the PWM pulses, preventing it from radiating into the surrounding environment. A properly shielded VFD power cable keeps EMI within the cable, protecting nearby sensitive equipment.
Bearing-Current Risk Reduction
The shield provides a low-impedance return path for high-frequency common-mode currents. By directing more of these currents back to the drive through the intended bonding path rather than through the motor bearings, the shield can reduce the risk of electrical discharge machining (EDM) that pits bearing surfaces. Shielding alone may not eliminate every type of bearing current; some systems also require measures such as shaft grounding, insulated bearings, common-mode chokes, or output filters.
Consequences of Improper or Missing Shielding
Improper shielding or termination can contribute to several system-level problems:
- Motor bearing-current risk: Poor high-frequency grounding can increase shaft voltage and the risk of EDM-related bearing damage.
- Instrumentation interference: Radiated or conducted EMI can cause unstable readings or communication errors in nearby sensors, control circuits, and industrial networks.
- EMC compliance failures: Inadequate shield continuity or termination can increase electromagnetic emissions beyond applicable limits.
- System reliability issues: High-frequency common-mode currents may find unintended return paths through equipment frames, grounding conductors, or connected machinery.
- Shielding alone does not eliminate all VFD-related electrical stresses. Long motor leads can also produce reflected-wave peak voltages that increase motor-winding insulation stress. Follow the drive manufacturer’s maximum cable-length limits and use output reactors, dv/dt filters, or sine-wave filters when required.
VFD Power Cable Shielding Types Compared
Understanding the different VFD power cable shielding options is essential for selecting the right cable for each application.
Copper Braid Shield
Construction: Tinned copper wire braid woven over the cable core
Coverage: 85% typical; higher coverage available with denser braid
Shielding performance: Provides a robust conductive path and effective EMI suppression when coverage, transfer impedance, and termination are appropriate for the application
Key characteristics:
- High mechanical strength and flexibility
- Low DC resistance for effective low-frequency noise return
- Durable under repeated flexing and vibration
- Can be used with standard termination hardware
Typically recommended for: Most industrial VFD applications, including pumps, fans, conveyors, and general-purpose installations requiring good low-frequency EMI suppression and mechanical durability.
Copper Tape Shield
Construction: Copper tape helically wrapped over the cable core with overlap (typically 25% minimum)
Coverage: 100%
Shielding performance: Continuous coverage can provide effective EMI containment when tape conductivity, overlap, cable construction, and termination are properly designed
Key characteristics:
- Full coverage eliminates gaps found in braided shields
- Continuous coverage can support effective suppression of high-frequency switching noise
- Thinner profile than braided shields
- Requires careful handling to avoid tearing
Typically recommended for: High-frequency noise-sensitive environments, papermaking, steel, metal processing, and applications with significant high-frequency harmonic content.
AL-PET Foil Shield
Construction: Aluminum foil laminated with polyester film, applied longitudinally or helically
Coverage: 100%
Shielding performance: High coverage can provide effective high-frequency EMI and RFI containment, subject to the foil construction, drain path, and termination method
Key characteristics:
- Lightweight and low cost
- 100% coverage for high-frequency noise
- Less mechanically robust than braid
- Can tear under vibration
Typically recommended for: Light-duty applications, weight-sensitive installations, and applications where high-frequency protection is the primary concern.
Combination / Double Shield
Construction: Foil (100% coverage) plus tinned copper braid (80-85% coverage)
Shielding performance: Can provide broad-band EMI control by combining high coverage with a mechanically robust conductive path
Key characteristics:
- Best of both shielding technologies
- Foil provides continuous coverage, while the braid adds a robust conductive path and mechanical protection
- Most comprehensive EMI suppression
Typically recommended for: Demanding industrial environments, papermaking, petrochemical, metallurgical applications, and any installation with severe EMI concerns.
Shielding Comparison Summary
| Shield Type | Coverage | Low-Freq EMI | High-Freq EMI | Mechanical Strength | Flexibility | Cost |
| Copper Braid | 85% | Excellent | Good | High | High | Moderate |
| Copper Tape | 100% | Good | Excellent | Moderate | Moderate | Moderate-High |
| AL-PET Foil | 100% | Moderate | Excellent | Low | High | Low |
| Combination | 100% | Excellent | Excellent | High | Moderate | High |
Flexible VFD Power Cable Options
Some applications require flexibility beyond standard VFD cables. Flexible VFD power cable designs use finer stranding and specialized jacket materials to accommodate moving installations.
When Flexibility Is Required
- Robotic applications: Cables that must flex continuously during operation
- Moving machinery: Cable tracks and drag chains
- Frequent reconfiguration: Temporary installations and mobile equipment
- Tight spaces: Installations with limited bending radii
Key Specifications for Flexible Cables
- Conductor construction: Class 5 or Class 6 fine-stranded copper may improve flexibility, but does not by itself establish a continuous-flex rating.
- Static bend radius: The minimum radius permitted during fixed installation.
- Dynamic bend radius: The minimum radius permitted during repeated movement; this is normally larger than the static bend radius.
- Flex-cycle rating: The tested number of bending cycles under specified operating conditions.
- Travel speed and acceleration: Important for drag-chain and high-speed machinery applications.
- Torsion rating: Required when the cable is exposed to repeated twisting.
- Jacket material: Flexible PVC, polyurethane, TPE, or another material selected for the required resistance to oil, abrasion, chemicals, and temperature.
For drag chains, robotics, or repeated-motion applications, verify the manufacturer’s dynamic bend radius, travel speed, acceleration, torsion limits, and tested flex-cycle life. Do not assume that every flexible VFD cable is suitable for continuous flexing.
Type TC VFD Cable and Tray Cable Applications
Type TC VFD cable refers to VFD cables rated for tray cable (TC) applications under UL standards.
What Type TC Means
UL Type TC (Tray Cable) designation indicates that the cable meets the basic construction and performance requirements for installation in cable trays as specified in UL Standard 1277.
Additional features—such as sunlight resistance, direct burial suitability, or hazardous location approval—are not automatically included with the Type TC rating. These properties require separate certification or specific construction requirements. Buyers should verify which optional features are actually covered by the specific product listing.
Key clarification:
- Type TC = Tray cable listing under UL 1277 (Type TC is the base tray cable listing under UL 1277)
- Sunlight resistance = Not automatic; requires UV‑rated jacket materials
- Direct burial = Not automatic; requires specific construction and testing
- Hazardous location (Class I, Division 2) = Not automatic; requires additional certification
- Temperature rating = Varies by cable design; 90°C wet/dry is common but not universal
Type TC-ER (Exposed Run)
Type TC-ER is Type TC cable that carries an additional exposed-run marking. It may be installed outside cable trays only in the specific exposed-run applications permitted by the NEC and local regulations. Permitted locations, support and securing requirements, mechanical protection, and cable markings must be confirmed for the specific product and jurisdiction.
Standard Type TC does not automatically carry the TC-ER exposed-run permission. Installation outside a tray depends on the applicable code provisions, the cable’s complete listing and markings, the location, and any required raceway or mechanical protection.
Where the applicable code permits an exposed run, TC-ER may reduce the need for additional raceway, simplifying installation and potentially reducing material and labor. This does not create a general permission for unrestricted exposed installation.
VFD Cable Shielding Termination and Grounding Best Practices
The best VFD power cable shielding is useless if not terminated correctly. Proper termination is critical for effective EMI suppression and bearing current protection.
The Golden Rules of VFD Cable Termination
Rule 1: Provide Low-Impedance Shield Bonding at Both Ends
For most VFD motor-cable installations, the shield should be bonded at both the drive and motor ends using low-impedance, preferably 360°, connections. The final arrangement must follow the drive, cable, and motor manufacturers’ instructions and applicable electrical codes.
Rule 2: Maintain Shield Continuity
Where practical, run the shield continuously from the drive to the motor. If an intermediate enclosure or connector is unavoidable, preserve 360° shield continuity and equipotential bonding in accordance with the approved system design.
Rule 3: Use 360° Shield Termination
Use 360° shield connections where specified to provide a low-impedance high-frequency path. Long pigtail connections are generally not recommended for VFD motor cables because their inductance increases impedance at high frequencies.
Rule 4: Bond to Clean Conductive Surfaces
Make shield bonds to clean conductive surfaces or designated grounding hardware as specified by the equipment manufacturer. Paint, oxidation, and loose hardware can increase connection impedance and reduce shielding effectiveness.
Termination Methods
Method 1: Constant-Force Spring or Approved Shield Band
For cable constructions that permit this method, an approved constant-force spring or shield band can provide circumferential contact between the shield and the designated bonding hardware. Follow the cable and drive manufacturers’ termination instructions.
Method 2: EMC Cable Glands
A correctly selected EMC cable gland can provide circumferential shield contact at an enclosure or motor entry. Whether the gland is used as the primary shield bond or as part of a different termination arrangement depends on the cable construction, gland design, enclosure bonding, and equipment manufacturer’s instructions.
Do not assume that one EMC-gland arrangement applies to every VFD cable. Some systems require a 360° bond at the enclosure entry, while certain cable constructions use a different manufacturer-approved termination method. Verify the complete drive-cable-motor installation instructions.
Method 3: 360° Shield Bonding Clamps
Approved 360° shield clamps mounted on a clean conductive backplate, grounding plate, or designated bonding bar can provide a resilient, low-impedance connection when this method is specified for the drive and cable system.
Common Termination Mistakes
Mistake 1: Unapproved Single-Ended Shield Termination
For most VFD motor-cable installations, bonding the shield at only one end does not provide the intended low-impedance high-frequency return path. Use single-ended or hybrid arrangements only when specifically required by the equipment manufacturer or system design.
Mistake 2: Pig-Tail Terminations
Pig-tail connections (twisted wire tails) increase impedance at high frequencies, reducing shielding effectiveness.
Mistake 3: Applying One Enclosure-Entry Method to Every Cable
Do not assume that the shield must always be bonded—or must never be bonded—at the enclosure entry. The correct arrangement depends on the cable construction, EMC gland, enclosure bonding, and drive manufacturer’s instructions.
Where a 360° entry bond is specified, use approved EMC hardware and maintain a short, low-impedance connection to the bonded enclosure structure. Where a cable manufacturer specifies an internal termination instead, follow that documented method. In all cases, maintain shield continuity and protective-earth connections as required.
Mistake 4: Using an Unapproved Cable Construction
A general-purpose power cable may not provide the shielding, grounding symmetry, insulation system, or capacitance characteristics required by a particular VFD installation. Use a cable construction approved by the drive manufacturer and applicable codes; otherwise EMI, insulation stress, and bearing-current risk may increase.
Installation Best Practices
- Maintain shield continuity: The shield and jacket should be intact all the way back to the drive
- Run cable continuously: Run the VFD cable continuously from the drive directly to the motor without intermediate connectors
- Use the specified bending radius: Follow the cable manufacturer’s minimum bend radius for fixed installation and, where applicable, repeated-flex operation
- Observe the installation temperature: Install and handle the cable only within the manufacturer’s specified temperature range
- Keep VFD cables separate: Separate VFD power cables from signal and control cables to prevent EMI coupling
Conclusion
VFD power cable shielding is not merely a construction detail—it is a functional part of the drive system’s EMC and high-frequency grounding design. Its performance depends not only on the shield material, but also on shield conductivity, coverage, transfer impedance, cable construction, routing, and termination. Choosing an appropriate shield construction—based on conductivity, coverage, transfer impedance, mechanical requirements, cable geometry, and the approved termination method—is only half the solution. Proper termination at both ends, using 360° connections on clean, paint-free surfaces, is equally critical.
Key takeaways:
- VFD power cable shields should generally be bonded at both the drive and motor ends using the low-impedance method specified by the equipment manufacturer
- Shield constructions include copper braid, copper tape, AL-PET foil, and combination shields; selection should consider conductivity, coverage, transfer impedance, mechanical duty, and termination
- Flexible VFD cables use fine-stranded conductors for moving applications
- Type TC identifies a tray-cable listing; direct-burial, sunlight-resistance, wet-location, and TC-ER capabilities must be verified from the markings and listing of the specific cable
- Common mistakes include unapproved single-ended termination, long pigtails, loss of shield continuity, and using a cable construction not approved for the drive system
GENGU CABLE provides a full range of 0.6/1kV VFD power cables with multiple shielding options—copper braid, copper tape, and AL-PET foil shielding—supporting custom requirements for industrial applications worldwide. Proper selection and installation of the VFD power cable can improve system reliability, reduce EMI and bearing-current risk, and support longer equipment life.
