By Eileen Harvey
In modern industrial automation, cables are lifelines that ensure accuracy, reliability and safety. Servo cables and variable frequency drive (VFD) cables are critical in transmitting both power and sensitive control signals. However, these systems often operate in environments full of electrical noise, harmonics and electromagnetic interference (EMI). This is where the importance of shielding becomes paramount. The shielding surrounding these cables acts as a protective barrier, significantly mitigating the impact of external interference on the signals carried within.
By enhancing signal integrity, shielding both improves the performance of motors and contributes to the overall longevity of the equipment. In industrial settings, where the stakes are high and the margin for error is minimal, the implementation of properly shielded cables can mean the difference between smooth, efficient operation and unexpected disruptions.
Understanding Shielding in Industrial Cables
Shielding is a protective conductive layer usually made from copper braids, aluminum foil or a combination that surrounds the insulated conductors inside a cable. Its purpose is to block external electromagnetic noise and prevent internal signals from leaking out.
Three of the most popular shielding materials are copper braid, aluminum foil and combination shields. Copper braid is flexible and strong and has excellent EMI protection. Aluminum foil is lightweight and effective at high frequencies. Combination shields offer superior overall performance.
The two types of shielding are overall shielding, which encloses all conductors inside the cable, and individual pair shielding, which protects each conductor pair and is ideal for sensitive feedback/encoder signals.
By using shielding correctly, industries can reduce costly downtime and avoid malfunctions in sensitive automation systems.
Shielding in VFD Cables
Variable frequency drives adjust motor speed and torque by varying frequency and voltage, but this process generates high-frequency switching noise and harmonics that can affect both the motor and nearby equipment. Shielding is essential because it prevents EMI from radiating into surrounding electronics, reduces common mode currents that can damage motor bearings, helps facilities comply with Electromagnetic Compatibility regulations and protects nearby communication lines and sensors from interference. Without proper shielding, a VFD cable can create radiated noise that causes a nearby PLC to malfunction, whereas a shielded VFD cable preserves motor efficiency and supports overall plant reliability.
Shielding in Servo Cables
Servo cables carry both power and feedback signals that enable precise motor control, and any interference in the feedback line can lead to incorrect positioning, jerky movements or complete system failure. Shielding prevents EMI and crosstalk from disrupting encoder signals, ensures accurate speed and position feedback to controllers and supports dependable operation in robotics, CNC machines and automated assembly lines. By maintaining signal integrity, shielding also reduces downtime caused by feedback errors. In a robotic arm, even a slight EMI related disruption in encoder feedback can produce misaligned components, while a properly shielded servo cable maintains pinpoint accuracy for smooth, uninterrupted production.
Benefits of Shielding in Both Servo and VFD Cables
- Reduces EMI and RFI: Protects sensitive signals and equipment.
- Enhances Safety: Minimizes fire and shock hazards from stray currents.
- Boosts Motor Performance: Stable voltage and current improve efficiency.
- Extends Equipment Lifespan: Prevents premature wear in motors and bearings.
- Ensures Standards Compliance: Meets UL, CSA, CE and IEC regulations.
When Selecting a Shielded Cable
Several factors should guide the choice of shielding. The environment matters because high EMI areas often require double shielding for adequate protection. Motor size and operating frequency also influence the level of shielding needed, with larger motors generating more electrical noise and therefore benefiting from heavier shielding. Cable routing plays a role as well; cables that run close to data or communication lines should have enhanced shielding to prevent interference. Proper termination and grounding are essential because shielding is only effective when it is correctly grounded.
Tips and Recommendations
Shielding should always match the needs of the application, and there is no benefit in paying for double shielding unless the system requires it. Proper grounding must be maintained to prevent floating noise that can undermine cable performance. VFD and servo cables should be routed separately from low voltage communication lines to reduce the chance of interference. Using high quality shielded options such as TKD Kabel’s Kaweflex series helps ensure long term reliability in demanding industrial environments.
FAQs About Shielding in Servo and VFD Cables
Q1: Do all VFD cables need shielding?
A: Yes. Without shielding, VFDs generate EMI that can cause equipment malfunctions and safety risks.
Q2: Can I use regular power cables instead of shielded servo cables?
A: No. Regular power cables cannot protect sensitive encoder signals, leading to inaccurate motor control.
Q3: What’s the difference between foil and braid shielding?
A: Foil is better for high-frequency noise, while braid is better for mechanical durability and low-frequency EMI.
Q4: How do I ground shielded cables properly?
A: The shield should be grounded at one or both ends, depending on system design, to maximize EMI suppression.
Shielding is not an optional feature; it’s a necessity for reliable and safe operation of servo and VFD cables. From reducing EMI to ensuring accurate signal transmission, shielding enhances motor performance and safeguards entire automation systems.
Explore the full range of TKD Kabel through L-com. We’ll fill your orders fast, with same-day shipping on all qualified, in stock, online orders received Monday through Friday before 5 p.m. EST. For TKD-related inquiries, connect with our U.S-based TKD expert Eileen Harvey at eharvey@infiniteelectronics.com.
