Best

machinevision cable factory

Shielding Effectiveness of Machine Cable: Everything You Need to Know

In industrial environments, machine cables serve as the “nervous system” of equipment, transmitting power and data between controllers, motors, sensors, and other critical components. However, these environments are filled with electromagnetic interference (EMI) from sources like variable frequency drives (VFDs), servo motors, high-voltage lines, and wireless devices. Uncontrolled EMI can disrupt signal integrity, cause equipment malfunctions, and even lead to costly production downtime. This is where shielding effectiveness (SE) of machine cables becomes indispensable. As a key performance 指标 (indicator) for industrial cables, SE directly determines a cable’s ability to block external EMI and prevent internal signals from leaking—making it a top concern for engineers, procurement managers, and facility operators when selecting machine cables.

1. What Is Shielding Effectiveness (SE) for Machine Cables?

Shielding effectiveness (SE) quantifies a cable’s ability to attenuate (reduce) electromagnetic radiation, both incoming (to protect internal signals from external EMI) and outgoing (to prevent internal signals from interfering with other devices). It is measured in decibels (dB), a logarithmic unit that reflects the ratio of the EMI intensity before and after passing through the cable’s shielding layer.

A higher dB value indicates better shielding performance:

20–30 dB: Basic shielding, suitable for low-interference environments (e.g., small workshops with minimal electronic equipment). It blocks ~99% of EMI.
30–50 dB: Moderate shielding, ideal for general industrial settings (e.g., assembly lines with standard motors). It blocks ~99.9% to ~99.999% of EMI.
50–80 dB: High shielding, required for high-sensitivity applications (e.g., medical equipment, precision automation). It blocks over 99.999% of EMI.
80+ dB: Ultra-high shielding, used in critical environments (e.g., aerospace, nuclear facilities) where even minimal EMI can cause catastrophic failures.

For most industrial machine cables, the SE requirement typically falls between 30–60 dB, depending on the severity of the EMI source and the sensitivity of the connected equipment.

2. Key Factors Influencing the Shielding Effectiveness of Machine Cables

The SE of a machine cable is not a fixed value—it is shaped by four core factors: shielding material, shielding structure, cable design, and external environment. Understanding these factors helps users select cables that meet their specific EMI protection needs.

2.1 Shielding Material

The choice of shielding material directly impacts SE, as different materials have varying electrical conductivity and magnetic permeability (ability to absorb magnetic fields):

Copper: The most common shielding material for machine cables. It has excellent electrical conductivity, making it highly effective at blocking high-frequency EMI (1 MHz–1 GHz). Copper shielding also offers good flexibility, which is essential for cables that need to bend (e.g., robot arm cables). However, it is heavier and more expensive than alternatives.
Aluminum: A cost-effective alternative to copper. It has lower conductivity than copper but is lighter and more corrosion-resistant. Aluminum is often used in foil shielding (see Section 2.2) for medium-frequency EMI (100 kHz–1 MHz) and is ideal for cables in outdoor or humid industrial environments (e.g., solar farms, wind turbines).
Steel: Offers high magnetic permeability, making it superior at blocking low-frequency EMI (50 Hz–100 kHz) from sources like transformers or power lines. Steel shielding is also highly durable and resistant to mechanical damage, making it suitable for harsh environments (e.g., mining, heavy machinery). However, it is rigid and less effective at high frequencies.
Alloys (e.g., Copper-Nickel, Tin-Plated Copper): Combine the advantages of multiple metals. For example, tin-plated copper enhances corrosion resistance while maintaining copper’s high conductivity, making it ideal for food processing or pharmaceutical facilities where hygiene and durability are critical.

From left to right: Copper braid, aluminum foil, steel tape, tin-plated copper braid.

2.2 Shielding Structure

The way the shielding material is applied (shielding structure) also affects SE, as it determines the coverage and integrity of the shield:

Braid Shielding: Made by weaving thin metal wires into a mesh around the cable’s inner conductor. The key metric here is coverage percentage (the area of the cable covered by the braid). A coverage of 85%–95% provides excellent SE for high-frequency EMI, while 70%–80% is sufficient for general use. Braid shielding is flexible and resistant to tearing, making it ideal for cables that move (e.g., conveyor belt cables).
Foil Shielding: Consists of a thin layer of metal (usually aluminum) bonded to a plastic film (e.g., polyester). It provides 100% coverage, which is critical for blocking low-level EMI and preventing signal leakage. However, foil shielding is less flexible and can tear if bent repeatedly, so it is often used in fixed applications (e.g., control panel cables). For enhanced performance, some cables use a “foil + braid” hybrid structure—combining the 100% coverage of foil with the flexibility of braid.
Tape Shielding: Made by wrapping metal tape (e.g., steel or copper) around the cable. It is durable and effective at blocking low-frequency EMI but has gaps between tape layers (reducing coverage to ~90%), so it is typically used in heavy-industry cables (e.g., mining equipment).

2.3 Cable Design and Grounding

Even the best shielding material and structure will fail if the cable is poorly designed or grounded incorrectly:

Shielding Layer Thickness: Thicker shielding layers provide higher SE, but they also increase the cable’s weight and cost. For most industrial applications, a shielding thickness of 0.1–0.3 mm (for foil) or 0.2–0.5 mm (for braid) balances performance and practicality.
Grounding: The shielding layer must be properly grounded to “drain” intercepted EMI to the earth. Poor grounding can turn the shield into an antenna, amplifying EMI instead of blocking it. Two common grounding methods are:
Single-Point Grounding: Grounding the shield at one end (e.g., the controller side). Suitable for low-frequency EMI (<1 MHz), as it prevents ground loops (currents that flow between multiple ground points).
Multi-Point Grounding: Grounding the shield at multiple points (e.g., both the controller and motor sides). Suitable for high-frequency EMI (>10 MHz), as high-frequency signals require a short path to ground.
Inner Insulation: The insulation between the inner conductor and the shielding layer must be made of high-quality materials (e.g., PVC, TPE) to prevent signal leakage and protect the shield from corrosion.

2.4 External Environment

The industrial environment itself can degrade SE over time:

Temperature: Extreme temperatures (e.g., >80°C in foundries or <–20°C in cold storage) can cause shielding materials to crack or lose conductivity. For high-temperature applications, cables use heat-resistant shielding (e.g., nickel-plated copper).
Moisture and Chemicals: Humidity, oils, and corrosive chemicals (e.g., in chemical plants) can corrode metal shielding. Cables for these environments use waterproof jackets (e.g., polyurethane) and corrosion-resistant shielding (e.g., aluminum or tin-plated copper).
Mechanical Stress: Cables in moving equipment (e.g., robots, cranes) are subjected to bending, twisting, and abrasion. This can damage the shielding layer, reducing SE. Flexible shielding structures (e.g., fine copper braid) and durable jackets (e.g., TPE) help mitigate this.

3. Testing Standards and Methods for Shielding Effectiveness

To ensure machine cables meet SE requirements, they must be tested according to international standards. The most widely used standards for industrial cables are:

3.1 IEC 61196 (International Electrotechnical Commission)

IEC 61196 is the global standard for coaxial and symmetrical cables, including machine cables. It specifies two key SE tests:

Shielding Attenuation Test: Measures the reduction in EMI intensity after passing through the cable’s shield. The test uses a shielded chamber (to eliminate external interference) with a signal generator (to produce EMI) and a receiver (to measure EMI before and after the cable).
Transfer Impedance Test: Evaluates how easily EMI flows through the shielding layer. A lower transfer impedance indicates better SE—for industrial machine cables, the transfer impedance should be <100 mΩ/m at 1 MHz.

3.2 ANSI/TIA-568-C.2 (American National Standards Institute)

This standard is widely used in North America for industrial and commercial cables. It requires machine cables to have a minimum SE of 30 dB at 100 MHz for general use and 50 dB at 1 GHz for high-sensitivity applications.

3.3 Test Setup Example

A typical SE test for machine cables involves:

Placing the cable in a shielded anechoic chamber (to block external EMI).
Connecting one end of the cable to a signal generator (to simulate EMI sources like VFDs).
Connecting the other end to a spectrum analyzer (to measure the EMI that passes through the shield).
Calculating SE using the formula: SE (dB) = 20 × log₁₀ (E₁ / E₂), where E₁ is the EMI intensity before the shield, and E₂ is the intensity after the shield.

A shielded anechoic chamber used to test the SE of industrial machine cables.

4. SE Requirements for Different Industrial Applications

The required SE of a machine cable varies by industry, depending on the type and intensity of EMI present. Below are common applications and their typical SE needs:

4.1 Automation and Robotics

Automation lines (e.g., automotive assembly) use VFDs, servo motors, and sensors—all of which generate high-frequency EMI (1 MHz–1 GHz). Machine cables here need an SE of 50–60 dB to prevent signal errors (e.g., sensor misreads) that can stop production. Hybrid “foil + braid” shielding is ideal, as it combines 100% coverage with flexibility for robot arm movement.

4.2 Medical Equipment

Medical machines (e.g., MRI scanners, ultrasound devices) are highly sensitive to EMI and also generate strong magnetic fields. Cables for these applications require 60–80 dB of SE to avoid disrupting patient data and ensure compliance with standards like IEC 60601. Copper braid shielding with a thick insulation layer is often used, as it blocks both EMI and magnetic interference.

4.3 Energy and Power Generation

Wind turbines, solar inverters, and power plants have low-frequency EMI (50 Hz–100 kHz) from transformers and high-voltage lines. Machine cables here need an SE of 40–50 dB and must be durable enough to withstand outdoor conditions. Steel tape or aluminum foil shielding (with a waterproof jacket) is preferred for its resistance to corrosion and low-frequency EMI blocking.

4.4 Food and Beverage Processing

Food plants use washdown equipment (e.g., high-pressure hoses) and have strict hygiene standards. Cables here need an SE of 30–40 dB (for general EMI protection) and must be resistant to water, chemicals, and high temperatures. Tin-plated copper braid shielding with a polyurethane jacket is ideal, as it is corrosion-resistant and easy to clean.

Top row: Automation robot cable, medical equipment cable; Bottom row: Solar inverter cable, food processing cable.

5. How to Select Machine Cables Based on Shielding Effectiveness

Selecting the right machine cable for your SE needs involves four simple steps:

Step 1: Assess the EMI Environment

First, identify the EMI sources in your facility (e.g., VFDs, motors, wireless devices) and their frequencies. Use an EMI meter to measure the intensity of the interference—this will help you determine the minimum SE required. For example:

If your facility has VFDs (1 MHz–1 GHz), aim for SE ≥50 dB.
If you only have standard motors (50 Hz–100 kHz), SE ≥30 dB is sufficient.

Step 2: Match Shielding Material and Structure to Your Needs

Based on the EMI frequency and application conditions:

High-frequency EMI (>1 MHz): Choose copper braid (85%+ coverage) or hybrid “foil + braid” shielding.
Low-frequency EMI (<1 MHz): Choose steel tape or copper braid with high magnetic permeability.
Outdoor/humid environments: Choose aluminum or tin-plated copper shielding with a waterproof jacket.
Moving equipment: Choose flexible copper braid shielding.

Step 3: Verify Grounding Compatibility

Ensure the cable’s shielding structure is compatible with your grounding method:

Single-point grounding: Use braid or tape shielding (avoid foil, which can develop ground loops).
Multi-point grounding: Use foil or hybrid shielding (for 100% coverage and low impedance).

Step 4: Check Supplier Test Certifications

Always ask suppliers for test reports that confirm SE compliance with IEC 61196 or ANSI/TIA-568-C.2. Avoid cables without certification—they may not provide the SE you need, leading to equipment failures.

A step-by-step guide to selecting machine cables for optimal shielding effectiveness.

6. Maintaining Shielding Effectiveness Over Time

Even the best machine cables will lose SE if not maintained properly. Follow these tips to keep your cables performing:

Inspect Shielding Layers Regularly: Look for tears, corrosion, or loose wires in the shielding. Replace cables with damaged shields immediately—they can no longer block EMI.
Check Ground Connections: Ensure grounding terminals are tight and free of rust. Loose ground connections reduce SE by preventing EMI from draining to earth.
Avoid Over-Bending: Do not bend cables beyond their minimum bend radius (usually 5–10 times the cable diameter). Over-bending can crack foil shielding or break braid wires.
Clean Cables Properly: Use mild soap and water to clean cables (avoid harsh chemicals). Chemicals can corrode shielding materials, reducing SE.

An engineer inspecting the shielding layer of a machine cable to ensure SE performance.

7. Why Choose FRS Machine Cables for Superior Shielding Effectiveness?

When it comes to machine cables with reliable shielding effectiveness, FRS stands out as a trusted global manufacturer. For over 15 years, we have focused on designing and producing industrial cables that meet the strictest SE standards—helping customers in automation, medical, energy, and food processing industries reduce EMI-related downtime.

Here’s how FRS delivers superior SE performance:

Premium Shielding Materials: We use high-purity copper (99.9% conductivity) for braid shielding, corrosion-resistant aluminum for foil shielding, and durable steel for tape shielding—ensuring optimal EMI blocking for any frequency.
Customizable Shielding Structures: Whether you need 95% coverage copper braid for robot cables, “foil + braid” hybrid for medical equipment, or steel tape for mining machinery, we tailor the shielding structure to your application.
Strict Quality Testing: Every FRS machine cable undergoes SE testing in our in-house shielded chamber, complying with IEC 61196 and ANSI/TIA-568-C.2. We provide detailed test reports with every order, so you can trust the SE performance.
Expert Grounding Guidance: Our engineering team helps you select the right grounding method (single-point or multi-point) for your EMI environment, ensuring your cables deliver maximum SE.
Durable Designs for Longevity: FRS cables use wear-resistant jackets (PVC, TPE, polyurethane) and flexible shielding to withstand bending, moisture, and chemicals—maintaining SE for up to 10 years in harsh industrial conditions.

From standard cables with 30–50 dB SE to custom solutions with 80+ dB SE for critical applications, FRS has the expertise to meet your needs. Our global network of distributors ensures fast delivery, and our after-sales team provides maintenance support to keep your cables performing at their best.

Choose FRS machine cables—protect your equipment from EMI, minimize downtime, and ensure reliable production.

FRS machine cables in production, featuring customizable shielding structures for industrial applications.

Conclusion

Shielding effectiveness is a critical factor in ensuring the reliability of machine cables in industrial environments. By understanding SE definition, influencing factors, testing standards, and selection methods, you can choose cables that block EMI and prevent equipment failures. For machine cables with consistent, certified SE performance, FRS is your ideal partner—combining premium materials, custom designs, and expert support to meet your unique needs.