VFD Cables – Their Importance and Uniqueness in Use with Variable Frequency Drive (VFD) Motors
Using Variable Frequency Drives (VFDs) allows precise control of the speed of three-phase motors, but it also introduces electrical stress and sensitivity to electromagnetic interference, common-mode currents, and harmonics—phenomena that standard cables are not designed to handle. Therefore, it is recommended to use a dedicated VFD cable.
What is a VFD Cable?
A VFD cable is a three-phase power cable that transfers energy from the drive (inverter) to the motor while meeting special requirements:
- Rapid voltage transitions
- High dv/dt (rate of voltage change)
- Momentary voltage peaks
- Common mode currents
- Electromagnetic interference (EMI/RFI)
- Harmonics – waveform distortions that damage sensitive components
Why Not Use a Standard Cable?
Using standard cables such as NYCY or H07RN-F may lead to:
- Damaged insulation – Voltage peaks and sharp transitions can break down insulation over time.
- Dangerous return currents – Flowing through machine structures and damaging motor bearings.
- Electromagnetic interference – The cable both emits and receives electrical noise.
- Worsened harmonics – Causing vibration, overheating, and degraded performance.
- Failures and wear – Random malfunctions and accelerated aging.
Characteristics of a High-Quality VFD Cable
Feature | Description |
High dv/dt and peak voltage resistance | XLPE insulation (90°C) preferred over PVC (70°C) |
Double electromagnetic shielding | Copper braid + aluminum tape provide full EMI protection |
Symmetrical conductors | Balanced geometric arrangement of phases and ground reduces magnetic fields |
Efficient grounding | Full-sized ground conductor helically laid with phases, or split into 3 conductors, improving EMC and current return |
Flexible copper conductor (Class 5) | Reduces damage from vibration and eases installation |
Environmental resistance | Protection from moisture, oil, UV, and vibrations |
Cable Construction and Symmetrical Grounding
What Are Symmetrical Conductors?
The three phases are laid geometrically around a central ground conductor, or each phase is accompanied by a closely aligned ground wire. This design reduces interference and magnetic fields.
Common Configurations:
- 3+3 Design: Three phase conductors + three split ground conductors laid helically. The ground wires fill the spaces between phase conductors, improving return current paths and magnetic balance. Preferred for cables of 6 mm² and above.
- Four symmetrical conductors: Three phase + one ground conductor of equal cross-section, helically twisted together. Used for smaller cables, typically up to 4 mm².
When Is a Dedicated VFD Cable Recommended?
- Cable length exceeds 10 meters
- Near sensitive equipment (e.g., PLCs, sensors)
- In shared trays with communication/control cables
- According to EMC standard requirements
- In critical industrial systems
Conclusion
VFD cables are designed to withstand the demanding conditions of systems with frequency converters: fast-changing voltages, electromagnetic noise, and harmonics.
They feature flexible copper conductors, high dielectric strength insulation, quality shielding, symmetrical conductor layout, and advanced grounding – ensuring stable, quiet, and safe long-term operation.
Investing in the right cable reduces faults, extends the life of motors and peripheral equipment, and improves overall system reliability.