Cable Shielding: Function, Form and Application
In modern electrical and electronic systems, cable shielding is fundamental to both performance and longevity. As signal speeds increase and installations become more complex, the need to manage electromagnetic interference while maintaining mechanical reliability has become more pronounced.
Shielded cables—often referred to as screened or braided cables—achieve this by incorporating a conductive layer around the internal conductors. This layer is typically formed from fine metallic wires woven into a mesh, though alternative screening methods are also widely used depending on the application.
What Defines a Shielded Cable?
A shielded cable incorporates an external conductive barrier applied over twisted or grouped conductors. In braided constructions, this barrier takes the form of interwoven strands of plain or tinned copper, arranged to provide a defined level of optical coverage.
Coverage levels are not fixed. While approximately 80 per cent optical coverage is common in many braided designs, this can be increased or reduced to suit electrical performance, flexibility or mechanical requirements. Higher coverage improves EMI attenuation, while lower coverage can increase flexibility and reduce overall weight. 
Managing Electromagnetic Interference
Electromagnetic interference (EMI) can originate from numerous sources, including adjacent cables, electrical machinery, radio frequency emissions and even the cable’s own conductors. Without adequate shielding, this interference can degrade signal quality, introduce noise or lead to system instability.
The conductive screen surrounding the cable acts as a controlled path for unwanted electromagnetic energy, preventing it from coupling with the internal conductors. When correctly grounded, the shield significantly improves signal integrity and consistency, particularly in sensitive data, instrumentation and control applications.
Mechanical Protection and Environmental Resistance
Beyond electrical performance, shielding also plays an important structural role. Braided screens add a degree of mechanical reinforcement, increasing resistance to abrasion, crushing and repeated flexing. This is particularly relevant in industrial settings, mobile installations or environments where cables are subject to vibration and physical stress.
In harsher conditions, shielding materials may also contribute to improved temperature tolerance and durability, extending the operational life of the cable.
Designing the Right Screening Solution
Cable shielding is rarely a one-size-fits-all solution. Effective design requires an understanding of the cable’s operating environment, including temperature, movement, exposure to interference and mechanical demands.
Screening can be incorporated during the initial cable design process or applied to an existing construction. This flexibility allows for bespoke solutions, whether the requirement is for minimal EMI protection within a compact cable or heavy-duty screening for demanding industrial use.
Materials Used in Cable Screening
The choice of shielding material directly influences both electrical and mechanical characteristics. Copper remains the most commonly used material due to its excellent conductivity, available in plain, tinned, oxygen-free and silver-plated forms. Each variation offers distinct advantages, from corrosion resistance to enhanced electrical performance.
Alternative metals such as aluminium, phosphor bronze, stainless steel and galvanised steel are used where specific strength, magnetic or environmental properties are required. In addition, non-metallic textile braids—including Nomex and high-strength aramid fibres such as Vectran—are employed where thermal stability or extreme durability is a priority.
Braid Construction and Coverage
Braided screens can be produced using a range of carrier counts, typically 16, 24, 32 or 48 bobbins. Increasing the number of carriers allows for finer wire distribution and higher optical coverage, while still maintaining flexibility.
Using multiple fine strands rather than fewer thicker wires helps preserve bend radius and movement, making braided shielding suitable for both static and dynamic applications. Cable diameters of up to 35 mm can be screened using these methods, with optical coverage levels reaching 100 per cent where required. 
Common Cable Shielding Methods
Different applications call for different shielding approaches. The most commonly used methods include:
Aluminium Foil Screening
Foil screening is a compact and cost-effective solution for applications with lower EMI exposure. It is typically paired with a drain wire to provide a grounding path while keeping overall cable size to a minimum.
Helically Lapped or Served Screens
Where flexibility is critical, a helically applied screen offers improved movement characteristics. This single-direction wrap is often used in retractable cables, individual cores or twisted pairs, particularly in high-temperature environments where foil alone may be insufficient.
Traditional Woven Braiding
Woven braids remain one of the most versatile shielding solutions. They offer adjustable coverage, strong mechanical protection and long-term durability. When constructed using fine wires, braided screens provide effective EMI attenuation without compromising flexibility.
Balancing Performance, Flexibility and Longevity
Selecting the appropriate shielding method involves balancing electrical performance with practical considerations such as flexibility, size and service life. Over-engineering can introduce unnecessary stiffness or cost, while under-shielding may compromise system reliability.
A standards-driven approach, supported by careful material selection and construction control, ensures that cable shielding performs as intended throughout its operational life.
