By Eileen Harvey
One of the most overlooked yet vital aspects of bus cable design is shielding. Proper shielding is essential because, without it, signals become vulnerable to electromagnetic interference (EMI) and radio-frequency interference (RFI). Such interferences can disrupt operations, leading to unexpected downtime that could be detrimental to productivity and efficiency. In extreme cases, these disturbances can even damage sensitive equipment, leading to costly repairs or replacements.
Among the most employed techniques are foil and braid shielding, each presenting its own set of advantages and disadvantages. Foil shielding, made from thin layers of aluminum or copper, excels at providing a continuous barrier against high-frequency noise, making it particularly effective in environments with high EMI levels.
What Is Shielding in Bus Cables?
Shielding is a conductive barrier that surrounds the conductors in a cable to reduce electrical noise. Its main functions are protecting data signals from external noise sources such as motors, drives, or wireless systems, preventing crosstalk between adjacent cables, providing a grounding path to discharge unwanted signals safely, and ensuring compliance with Electromagnetic Compatibility (EMC) standards. In bus cables, shielding is indispensable because they often run in electrically noisy environments such as factories, power plants, and transportation systems.
Types of Shielding in Bus Cables
Foil Shielding
Foil shielding uses a thin layer of aluminum or copper laminated to polyester film, which is wrapped around the conductors. This type of shielding provides 100% coverage even over long cable runs. It is lightweight, cost-effective, and excellent at blocking high-frequency interference. However, foil shielding is not as durable against flexing, can crack over time, and offers less mechanical strength compared to braids. Its higher resistance also makes it less effective for low-frequency noise. Foil shielding is best used in fixed installations where cables do not move frequently and in applications that require full coverage from high-frequency EMI.
Braid Shielding
Braid shielding is made of woven copper or tinned copper wires that form a mesh around the cable core. It is extremely durable and flexible, provides superior low-frequency noise suppression, and offers a low-resistance path for grounding. Braid shielding also adds mechanical strength, protecting the cable from wear. Its limitations include partial coverage, typically between 70 and 95 percent, and greater weight and cost compared to foil shielding. This type of shielding is best suited for environments with frequent cable flexing or mechanical stress and for applications requiring strong grounding and mechanical durability. A common example is CAN-Bus cable with braided shielding.
Foil + Braid Combination (Hybrid Shielding)
Many industrial-grade bus cables use both foil and braid shielding to combine the strengths of each method. The foil provides 100% coverage against high-frequency EMI while the braid adds mechanical durability and better low-frequency shielding. Together, they offer unmatched performance in demanding environments. Hybrid shielding is most effective in high-noise environments such as factories with motors, variable frequency drives, and robotics. It is also valuable for long-distance communication where maintaining signal integrity is essential. An example is the CAN-Bus double-shielded cable.
Importance of Shielding in Bus Cables
Shielding plays a mission-critical role in the performance and reliability of bus cables. It prevents EMI and RFI, which is essential in industrial plants with motors, inverters, and radio equipment. It protects signal integrity to ensure accurate data transfer and avoid packet loss or errors. It also reduces crosstalk to maintain clean communication when multiple cables run in parallel and enhances safety and compliance by ensuring adherence to international EMC standards. Without proper shielding, cables can act like antennas, picking up or radiating interference that disrupts the entire communication system.
Choosing the Right Shielding for Applications
When selecting bus cable shielding, several factors must be considered. For frequency range, foil shielding works better for high-frequency interference, while braid shielding is more effective at low frequencies. For cable movement, foil is sufficient in fixed installations, but braid or hybrid shielding is essential in dynamic or flexible applications. For industrial environments, hybrid shielding is recommended in high EMI zones with motors, drives, or welding machines, whereas foil may be adequate in clean, controlled environments. Cost versus performance is another factor. Foil is less expensive, but braid and hybrids offer greater durability and reliability, which justifies the additional cost in critical applications. PROFIBUS cables, for example, often use foil combined with braid for balanced EMI protection, as seen in TKD Kabel PROFIBUS options.
Facts About Bus Cable Shielding
A braid shield with 95 percent coverage can outperform a foil shield in certain low-frequency environments. Some advanced industrial bus cables even use double braiding combined with foil for extreme EMI protection. Shielding effectiveness is measured in decibels (dB), and a higher dB rating indicates better protection.
Expert Tips for Better Shielding Performance
To maximize shielding performance, always ground the shield properly since a shield without grounding is ineffective. Avoid sharp bends that may damage foil shields, and choose stranded conductors with braid shielding for robotic or mobile equipment. Double-shielded cables should be used in environments with both low- and high-frequency noise. Finally, always check for EMC compliance before installation.
Recommended TKD Kabel Bus Cables
Here are some shielded bus cable options from TKD Kabel (via L-com): PROFIBUS Double Shielded Cable has foil + braid shielding for industrial automation; CAN-Bus Double Shielded Cable is designed for automotive and industrial CAN networks; and AS-i Bus Cables are for actuator-sensor communication in harsh environments.
Shielding is the silent guardian of bus cables. Without it, communication networks would be vulnerable to interference, downtime and costly failures. Foil shielding is best for fixed, high-frequency environments. Braid shielding excels in flexible, low-frequency, mechanically stressed conditions. Hybrid shielding offers the best overall protection in modern industrial environments.
When selecting cables, consider your application, environment and durability needs. For robust, high-quality options, explore TKD Kabel Bus Cables to ensure your communication systems remain efficient and interference-free.
About L-com
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.
