1. Best Practices for VFD Cabling
Peter Cox P.Eng.
Project Manager
Belden Industrial Cable

2. Peter Cox Bio Licensed Professional Engineer
Worked in or as a consultant to Industry for 28yrs – mostly in a Drives and Industrials Controls
Participated in the testing of the first VFD cables developed with a major drive manufacturer in 1995
Did Beta testing of the 1336 Impact drive at Belden

3. Learning Objectives Understand Belden’s VFD Product Line
Belden Premium VFD
Belden CTC Construction Grade VFD
Understand the 4 Reasons to Specify VFD Cable
Common Mode Current
Capacitive Coupling/Cable Charging
Reflected Wave Voltage
Safety and Reliability
Discussion of Paralleling

4. There is no standard for VFD cables Performance is all about Copper
One thing you need to Remember…..
There is no standard for VFD cables
Performance is all about Copper
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

5. VFD Cable Connects Motor and Drive Power Circuit
Provides Reliable and Robust Connection
Protects against harmful noise
The VFD cable transmits power from the drive to the motor.

6. Belden VFD Cable Product Offering Classic Foil/Braid Design
VFD Classic Cables
Four Conductor Foil / Braid Shield Design VFD Cables
(Three stranded TC Conductors + 1 Insulated Ground – green with a yellow stripe)
29500: 16 AWG VFD
29501: 14 AWG VFD
29502: 12 AWG VFD
29503: 10 AWG VFD
29504: 8 AWG VFD
29505: 6 AWG VFD
29506: 4 AWG VFD
29507: 2 AWG VFD
Advantages – This construction offers thicker insulation for better performance and extended transmission distance
Other Designs – Interlocked Aluminum and Steel armored VFD products (part numbers available in NP316)
Much More Copper than 3C designs – Compared to Construction Grade these cables have as much as 3 times the copper at ground potential. Nearly as much as is in the circuit conductors
When comparing, look at product weights.
More Info in NP 235

7. Belden VFD Cable Product Offering Symmetrical Design
VFD Classic Cables
Symmetrical Design VFD Cables
(Three stranded TC Conductors +
3 Symmetrical BC Grounds +
2 Spiral Copper Tape Shields)
29528: 1 AWG VFD
29529: 1/0 AWG VFD
29530: 2/0 AWG VFD
29531: 3/0 AWG VFD
29532: 4/0 AWG VFD
29533: 250 AWG VFD (2KV)
29534: 350 AWG VFD (2KV)
29535: 500 AWG VFD (2KV)
Advantages – The symmetrical ground design provides a balanced grounding system that is preferred in the industry on larger HP drives
Other Designs – Interlocked Aluminum and Steel armored VFD products (part numbers available in NP316)
More Info in NP 235
We use 2 copper tapes with twice the surface area for better high frequency conduction. Contra helically applied where possible for lower inductance and higher performance. Much more effective and more expensive than a single tape used on all other products.

8. Customer Drivers Challenges Requirements Belden
Application Issues
Customer Drivers
Energy Savings
Low Total Cost of Ownership
High Availability
Safety: People & Processes
Challenges
Common Mode Current
Capacitive Coupling and Cable Charging
Reflected Wave Voltage – Motor and Cable Life
Application Reliability and Safety
Requirements
Reliability - high MTBF
Manufacture recommendations
Resistance to harsh environment
NEC
There it NO STANDARD FOR VFD cables
Belden
Quality and higher MTBF components in the industry.
The only product in the market that was co-designed in conjunction with a major drives manufacturer
Global availability
17 years as a leading supplier of VFD cable

9. Application Issues Common Mode Current AKA Current Noise
Definition
Current that flows between the drive and motor by any path other than the 3 primary motor leads
Kirchhoff’s Law – The sum of current at any point is zero - All current must return to the drive somehow
Effects
Network Errors - Encoder Faults
Loss of signal reliability analog and digital signal error
Ground plan noise pollution
Motor bearing failures
False stops and safety circuit trips and alarms
EMI and RFI
Mitigation
Lowest Impedance ground path and Shielding Make the cable the most attractive path for HF currents
High Surface area (4-8x) Conductors reduce HF cable heating and reject less CMC
Why Belden
We put up to 3 times more copper at ground potential than competitors “VFD” cables – with flexible stranding we contain CMC 300% better on our premium VFD
Combination of foil braid, or 2 layers of CU enhances performance

10. What Does Common Mode Noise Look Like?

11. Motor Bearing Currents
High Voltage can also discharge through the bearings causing etching in the races and premature motor failure
This is a photo of failed bearings from a motor driven with a VFD. By not removing the electric charge that builds up in the motor windings via the ground wire and or low resistance shield path to ground, the electricity may also discharge through the motor windings causing a motor failure or through the bearings as shown here. The etched pattern in the bearings shown in these pictures is indicative of the frequency of the drive – this etching causes excessive noise and vibration in the motor before failure.

12. Application Issues Capacitive - Coupling Cable Charging
Definition
Current that leaves the drive but is lost due to capacitive interaction with other cables. (Cable Charging)
Effects
Loss of motor torque or stalling
False trips of drive overcurrent
reduced system efficiency
Charging of DE energized adjacent circuits
Human safety issues
Mitigation
Lowest Capacitance 150ma/kft /conductor for THHN vs. 50ma/kft/conductor for Belden VFD cable
Shielding to prevent interaction between systems
Why Belden
Superior shielding
Lowest capacitance

13. Application Issues Reflected Wave Voltage
Definition
A voltage spike originating at the motor, caused by the impedance miss match between the motor and cable
Effects
Motor failure and downtime
Cable failure (wet THHN)
Mitigation
Lowest Capacitance cable
Output reactor (an immediate 3-8% efficiency loss)
Why Belden
Our 600V cables have a minimum 5500V Corona inception voltage (CIV) wet THHN can be 1600V or less
Lowest capacitance increases distance before harmful voltages are created by up to 3x compared to THHN

14. Reflected Wave Voltage
Application Issues
Reflected Wave Voltage
Belden participates in a wide range of industrial markets where our products are used.

15. Application Issues Installation reliability and safety
Cable/motor failure and degradation with PVC/Nylon
Reference manufacturers cable selection instructions
System noise issues
Downtime
Liability

16. The 2kv Myth
Issues
In the 90’s VFDs lead to high failure rate on 600V THHN installations
The engineering community began to specify 2000V THHN as a result
600V VFD cable, even the weaker construction grade, has higher dielectric strength than 2Kv THHN
Belden has never had a claim for dielectric failure in 16 years making 600V VFD Cable
Code requirements are satisfied by 600V cable

17. Belden Features Feature Benefits
Foil Braid – Drain and full sized ground
Benefits
50% more copper than most 3C symmetric
-300% better common mode current protection
Enhanced flexibility

18. Belden Features Feature Benefits Flexible Stranding
4-8 times higher surface are means reduced High Frequency Losses
Cooler operation
Enhanced flexibility
Flexible motor supply rating

19. Belden Features Feature Benefits
Oversized wall thickness for lower capacitance (0.045 vs 0.030)
Benefits
Reduced cable charging current
Longer critical distances for reflected wave buildup
Longer cable life

20. Belden Features Feature Benefits Dual copper tapes
Better HF shielding than a single 5mil
Reduced noise
Enhanced flexibility

21. Belden Features Feature Benefits Tinned stranding Corrosion resistance
Thermal stability
Connection reliability

22. Belden Features Feature Benefits ER rating Reduced installation costs
Enhanced mechanical performance

23. A Comparison of Mitigation Strategies
Input Line Reactor
Output Line Reactor
Common Mode Choke
Motor terminator/snubber
VFD Cable
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

24. Input Line Reactor Feature Benefits
Adds impedance on the Line side of the drive
Benefits
Protect the drive from line transient damage
Reduces Overvoltage faults
Reduces Harmonic currents

25. Output Line Reactor Feature Effects
Adds impedance on the load side of the drive
Effects
Can be protective of non inverter motors
Reduces Dv/Dt rise time downstream of the reactor thus increases critical distance
Can have harmonic interaction with Motor
Has high associated efficiency losses (3-8%)
Reduces motor voltage and torque

26. Common Mode Choke Feature Effects Reduces common mode current
Reduction of common mode current
Reduces noise emissions
Does no reduce EMI or RFI at all

27. Motor Terminator/Snubber
Feature
Burns of reflected wave energy as heat at the motor
Effects
Reduction of reflected wave voltage
Protection of motor and cable systems
Great for vulnerable motors on very long leads

28. Pete Comber Competitive landscape
There is no standard for VFD cables, but we can categorize the product available:
Best:
Fine strand, tinned copper
XLPE Insulation
3 power conductors and 1 full size ground
Foil and braid shields
Manufacturers are in the on machine world
Better:
Stranded copper (some have tinned)
XLP or THHN insulation
3 power conductors and 3 reduced size grounds
Copper tape shield
Manufacturers are in the power cable market
Good:
Bare copper (think tray cable stranding)
THHN insulation
3 power conductors and 3 reduced size grounds
Copper tape shied
Manufacturers are from any background
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

29. Placeholder for Pete Comber Competitive landscape
There is no standard for VFD cables
Upgraded THHN
Construction Grade VFD XHHW
4C vs 3C Symmetric designs optimized for high frequency
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

30. Compared to THHN in Conduit
No Common Mode Current Containment or Shielding Do you want to put the noisiest signals in the plant in unshielded cable?
Cost does not include conduit and labor, with ER or Tray, these costs are dramatically reduced
Faster “Ring Up” of Reflected Wave Voltages
Higher cable charging current – Significant for small drives
Short cable life on long runs - 10yr MTBF estimates-Not rated for 1600V
No protection from capacitive coupling - Shielding
Conduit transitions have high HF impedance-Reduced surface area
Faults in THHN may not be catastrophic but periodic due to pin holes
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

31. When to use Belden C Series (Construction Grade)
There is no standard for VFD cables
When we are comparing to Service Wire/General etc. And there is no spec or performance standard
IF No Flexible Motor supply rating is required and flexibility is not desired
The environment is not noise sensitive
Cable Charging, and EMI, and RFI are the only issues
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

32. Advice for Proper Instalation
The following are best practices for VFD Cable installation and Termination:
Directly connect the Shield at the Motor and Drive Only
Do not introduce jumping off points for CMC through shield termination- Use Insulated glands
Do not cut the shield between the motor and drive
Do not use intermediate termination for the conductors if safely avoidable
Maintain maximum spacing from sensitive circuits and route cables away from instrumentation and networks
Reference the Belden VFD Termination guide
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

33. Advice for Proper Instalation
Using VFD Cables with Safety Disconnects
Run a separate ground to the safety disconnect
Avoid contact between the VFD cable grounds and shield with the ground in the disconnect
If you must cut the grounds, terminate through an isolating terminal block or connection
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

34. Termination videos
Run the Videos

35. A customer resiest VFD Cable because he always uses THHN without issue
Scenario Based Q&A
A customer resiest VFD Cable because he always uses THHN without issue
You may have issues you don’t know
Process measurement error
Overcurrent or ground fault trips
Loss of efficiency
Network errors
Remember that ground plane pollution is additive, one bad install may not cause a problem, but the accumulation of many bad installs may cause problems in the future
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

36. Scenario Based Q&A
A customer has contacted you because he experiences frequent motor failures on pumps driven by VFD’s
What Questions should you ask
How long are the motor leads
Is the motor wet
What type of failures
How large is the motor
What are the likely causes of failure
Reflected wave voltage
Bearing Currents
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

37. Could it be drive related?
Scenario Based Q&A
A customer experiences network drops on the mixer ever since the line was upgraded
Could it be drive related?
How is the drive cable run
How long are the motor leads
What type of cable has been used?
Does it correlate with drive starts stops enables
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

38. Scenario Based Q&A
A contractor has installed a large drive system for airport baggage handling. On commissioning many of the drives trip on overcurrent or will not run
What issue do you think is the likely cause
How long are the motor leads
What type of cable has been used?
When ever you talk about VFD cables, you need to consider what issues you potentially face in the application, and what cable design will be best suited to the application safety, performance, and reliability requirements.

39. Paralleling and TC-ER Rating
Installations savings
Material
No metal conduit
No metal clad cable
Labor
Less time
Maintenance
Simplifies equipment moves, no conduit to re-route / install

40. Parallel Conductors Sizing Parallel VFD Cable: Amps 1/0 2/0 3/0 4/0
250
350
500
Single
170
195
230
260
290
430
Parallel
340
390
460
520
580
700
860
Triplex
510
585
690
780
870
1050
1290
Quad
680
920
1040
1160
1400
1720
Per NEC (16)
When installed in Cable tray with air spacing, or in separate conduits
When parallel in Single conduit additional derate is required

41. Belden VFD Resources & Tools
Industrial Cable VFD Page on Belden Website
Unarmored VFD cable Termination Guide
VFD Cable solutions guide
Belden VFD Product Bulletin
Belden VFD Cable Selection guide (based on Motor HP)
Choosing the Right Cable for your Variable Frequency Drive (VFD) System White Paper
Building a Reliable VFD System White Paper
Control Engineering
1-800-Belden1