What is cable shielding? Everything you need to know
Shielded cables are a staple in industrial applications, offering vital protection against signal interference that would otherwise render cables useless. But how exactly does shielding protect from interference? What other benefits, if any, does shielding offer? And when is it better to stick with an unshielded cable? Read on to find out.
What is cable shielding?
Shielded cable is, simply, a cable with a conductive shield that protects against electromagnetic interference (EMI). The shield can either absorb or reflect incoming noise, and conduct it to the ground to prevent any from reaching the cable conductors.
What is electromagnetic compatibility protection?
Electromagnetic compatibility, or EMC, "is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment" (Source).
To ensure this protection, a cable must be electrically shielded. This protective effect is expressed strongly by the indication of the optical coverage of the shield. This is the area of the cable that is optically covered by the shield.
For example, if the cable has foil as its shield, it can be said to have 100% coverage. The optical coverage of our chainflex® cables can reach a value of 90% due to a shield consisting of tinned copper wires.
What benefits do shielded cables offer?
Shielded cables, along with protecting the integrity of signal transmissions, provide other unique benefits that can improve application design. Learn more about these benefits below.
Signal integrity
The primary function of a cable shield is to protect signals from EMI. This leads to improved signal integrity, as crosstalk and other forms of interference are prevented from impacting signal transmissions.
Stable performance
Another effect of preventing interference is more stable performance. While cable shields don’t technically increase data transmission speeds, they help ensure cables are more consistently reaching their top transmission speeds by protecting against EMI.
Improved durability
Cable shielding does more than just protect against interfering signals — it also adds an additional protective layer to the cable that helps increase durability. This makes cable shielding especially valuable in applications with frequent or continuous movement.
What are the different types of cable shields?
There are three major types of cable shielding: foil, braided, and spiral. Each has its own advantages and disadvantages, and no universal “best” option exists.
Foil Shielding: A thin layer of metallic foil that provides 100% cable coverage, making it excellent for high-frequency interference. However, it has poor mechanical strength and is not suitable for continuous flexing.
Braided Shielding: An interwoven mesh of conductive wires — typically copper — that offers superior mechanical strength, durability, and flexibility with good effectiveness at low to mid-frequencies, though coverage is typically limited to 70%–95%.
Spiral Shielding: Individual conductive wires wrapped helically around the core, providing excellent flexibility and up to 95% coverage, but it is primarily effective at low frequencies (like audio) and not usually recommended for high-frequency applications.
Both foil and braid shielding can be used on a single cable to combine the benefits of each — the high-frequency resistance and 100% coverage of foil shielding and the mechanically robust, low-frequency resistance of braided shielding.
What do you have to pay attention to when using a shield?
There are a few key considerations that need to be made when selecting a shielded cable for your application. Aspects like application environment, and type of motion in moving applications will all determine which type of shield is best suited for the application.
Application environment
The environment a cable is operating within is one of the biggest factors in if a shield is needed in the first place. Even in areas with large amounts of electrical noise, there are instances where shielding is unnecessary.
In low-noise environments — those which do not have many interfering signals — such as mid-sized offices, homes, or other similar indoor areas, it’s unlikely a shielded cable is necessary. What little EMI may reach the cable can be canceled out by using a twisted pair or star quad cable.
Further reading: Star quad cables & their advantages over twisted pair cables
Medium-noise environments are more akin to standard manufacturing plants, where motors, relays, and other equipment are a source of consistent interference. Shielding is recommended here, though the type of shielding will depend on application-specific factors.
High-noise environments consist of heavy-duty industrial environments where not only can large equipment create interference, but crosstalk from nearby cables as well. Unless a cable is within a metal cabinet that can protect it from EMI, it will need a shield in high-noise environments.
Type of motion
The type of motion a cable undergoes has a major part in which type of shielding is best suited to use. In any application with large amounts of movement, foil shielding is not usually recommended unless paired with a braided shield due to foil’s low mechanical strength.
For linear applications, it’s important to have a braided shield with a particularly flat braid angle. This is because a flat angle minimizes “windows” forming in the shielding that would allow interference to reach the cable conductors.
A shield with braid angles that are too acute or the use of foil shielding can often lead to error patterns such as shield breakage. To ensure that these faults do not occur, our shielded chainflex cables use either braided or spiral shielding, depending on the type of application.
Finally, spiral shielding is best suited for torsional applications. This is because high shield coverage can be maintained during torsional movements, as the shield can open and close to accommodate the movement of the cable.
Conclusion
Shielded cables are essential in industrial settings, providing vital protection against signal interference and ensuring signal integrity and stable performance. Beyond signal protection, the shielding also adds a layer of improved durability, which is especially valuable in applications involving frequent movement.
The best type of shield—foil, braided, or spiral—depends on the specific needs of the application, including the level of electrical noise in the environment and the type of motion the cable undergoes.
By understanding the unique benefits and drawbacks of each shielding type, you can select the right cable to maintain electromagnetic compatibility and ensure long-term, reliable operation.
Frequently Asked Questions
Cable shielding refers to the conductive layer that encloses a cable, typically made of braided wire, foil, or a combination of both. This layer acts as a barrier, protecting the signals within the cable from external electromagnetic interference (EMI) and preventing the signals from escaping and interfering with other devices.
Common materials include copper braid, aluminum foil, or metallized Mylar. Sometimes, multiple layers are used for enhanced protection.
Cable shielding is crucial for several reasons. Primarily, it's about managing electromagnetic interference (EMI) and radio frequency interference (RFI). Without shielding, external interferences can corrupt data, degrade signal quality, and even cause equipment malfunction.
EMI (Electromagnetic Interference) is any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades the effective performance of electronics. RFI (Radio Frequency Interference) is a subset of EMI, specifically referring to interference in the radio frequency range. Both can induce unwanted currents in cables, leading to signal distortion, data loss, and reduced system reliability.
While some cables are more susceptible than others (e.g., analog signals, high-speed digital data), virtually any cable can be affected by sufficient EMI/RFI. The environment in which a cable is deployed plays a significant role in determining the type of shielding required.
Yes! Not only can unshielded cables be affected by external interference, but they can also emit their own electromagnetic noise, potentially interfering with the operation of nearby electronic devices.
Yes, shielding can sometimes make a cable less flexible, especially if it's a heavy braid or multiple layers are used. However, advancements in shielding materials and designs aim to minimize this impact while still providing effective protection.
While shielded cable offers superior protection against EMI/RFI, it's not always strictly "better" for every application. For very short runs in low-noise environments, or for applications where cost and flexibility are paramount and interference is not a concern, unshielded cables might be sufficient. However, for most modern electronic systems, shielding is highly recommended.
