HELUKABEL flexible cables – Durable solutions for continuous motion applications

Flexibility and softness are two mechanical properties of electrical cables that are often confused.

1.1 Flexibility

Flexibility refers to a cable’s ability to bend, twist, or change shape at a given moment without causing damage to the conductor, insulation, or outer sheath. This characteristic indicates how well a cable can withstand movement, bending, or routing around complex structures during installation or operation.

Flexibility is typically evaluated through the minimum bending radius – the smallest radius a cable can be bent without compromising its electrical or mechanical performance. The bending radius depends on several factors, including the cable’s outer diameter, conductor structure (number of strands, strand diameter), and the type of insulation or sheath material.

In other words, a highly flexible cable can bend easily and maintain its bent shape without cracking the sheath, breaking conductor strands, or degrading its electrical/data transmission properties.

1.2 Softness of the conductor

Softness describes the degree of flexibility and ease of bending of the metal conductor itself – the part inside the cable responsible for electrical conduction. It reflects how well the conductor can withstand manual bending and shaping during installation without cracking or reducing its conductive cross-section.

Unlike flexibility, which considers the entire cable structure and its ability to endure long-term dynamic motion, softness focuses only on the conductor’s pliability. A softer conductor makes it easier to route cables in tight spaces while maintaining stable conductivity.

According to IEC 60228, conductor softness is classified into different classes:

• Class 1: Solid conductor (single wire), used in fixed/static applications.
• Class 2: Stranded conductor with a few wires (typically 7), used in low-vibration applications.
• Class 5: Flexible conductor with many fine strands, used in applications requiring free movement without strong tensile forces.
• Class 6: Extra-flexible conductor with very fine strands, used in drag chain systems or robotic applications.

The higher the level, the higher the softness of the conductive core.

FAQs: Frequently Asked Questions about the Conductor in Electrical Cables

2.1 Flexible installation cables (Flexible cables)

Flexible installation cables, often referred to in technical documents, are mainly evaluated based on their ability to bend easily and allow convenient handling during installation. These cables are ideal for routing around complex structures or for twisting to achieve a more aesthetic installation.

Once installed, these cables typically remain static, meaning flex life (the number of bending cycles a cable can withstand) is not a critical factor. Typical applications include cable trays, fixed wiring systems, household appliance connections, static industrial systems.

2.2 Dynamic flexible cable (Flex cables)

Dynamic flexible cables, also known simply as flex cables, are specifically engineered to endure repeated bending, twisting, and continuous movement while maintaining mechanical integrity and transmission performance. They are the optimal choice for continuously operating systems where conventional rigid cables would quickly degrade or fail.

Key features of flex cables:

1. High flexibility: Capable of withstanding millions of bending cycles at very small radii without cracking the insulation or breaking the conductor.
2. High durability: Optimized construction resists abrasion, vibration, and mechanical stress caused by continuous movement. Ideal for robotic arms, drag chain systems, automated conveyors, handheld devices, and machinery requiring frequent motion.
3. Lightweight with finely stranded conductors: Built with ultra-fine copper strands, making the cable thinner, lighter, and easier to route compared to rigid cables.

The ability of a flexible cable to bend, twist, and withstand continuous movement is primarily determined by the construction of its internal components. Each element - from the conductor to the outer sheath - directly impacts the cable’s overall flexibility.

3.1 Conductor – the most important factor

The flexibility of a cable originates mainly from the design and stranding technique of the conductor. By bunching many ultra-fine copper wires into strands, the cable achieves both greater pliability and a longer flex life, ensuring consistent electrical and mechanical performance throughout its service life.

Flexible cables typically use class 5 or class 6 stranded copper conductors as defined by IEC 60228, instead of class 1 or 2. The reason is that class 5 and class 6 conductors consist of a high number of fine copper strands twisted together. The smaller the strand diameter, the higher the cable’s bending capability and vibration resistance. This makes class 5 and 6 conductors ideal for robotics, conveyor systems, drag chains, and mobile equipment.

Explore the advantages and disadvantages of copper and aluminum conductive cores

3.3 Armour and shield

The armour and shield are critical supplementary components in cables, providing protection against mechanical stress and electromagnetic interference (EMI). However, these layers also have a direct impact on the flexibility and bending performance of flexible cables.

For example, galvanized steel wire (GSW) armor offers strong mechanical protection but significantly increases cable stiffness, reducing its overall flexibility.

In flexible cables requiring EMI protection, a tinned copper braid shield (with coverage up to 85%) is commonly used because it maintains cable pliability while still providing effective shielding. In contrast, an aluminum foil shield delivers 100% coverage but comes with the drawback of reduced bending radius and limited flexibility.

Learn about the structure of electrical cables and the role of each component

5.1 When should flexible cables be used?

Flexible cables are ideal for applications that require frequent bending and movement. They ensure stable transmission of power and signals while withstanding continuous motion without reducing service life or performance. Key applications include:

• Industrial automation: Automatic machinery, production lines, conveyors, and robotic arms - ensuring stable power and signal transmission in high-vibration environments.
• Robotics: Supporting complex, repetitive, and multidirectional movements, helping extend equipment lifespan and maintain precise functionality.
• Audio, video, and studio equipment: Microphones, musical instruments, speakers, and cameras - ensuring signal integrity while minimizing wear and tear during frequent handling.
• Renewable energy: Wind turbines and solar panels - withstanding outdoor conditions and adapting to the movement of blades or solar modules.

5.2 When are continuous-flex cables not the optimal choice?

Although flexible cables are highly advantageous for dynamic applications, there are certain scenarios where they may not be suitable because they cannot meet the required mechanical, electrical, or safety standards:

• Fixed wiring systems: Not recommended, as flexible cables may not comply with electrical standards and installation codes.
• High-stress or extreme temperature environments: Flexible cables are limited in scenarios with heavy mechanical loads or extreme heat/cold.
• Heavy-load applications: Long-term tensile or compressive forces can cause abrasion, damage, or breakage that exceeds the durability of standard flexible cables.
• Fire-resistance requirements: In environments where fire protection is critical, flexible cables may not always provide sufficient resistance. Specialized fire-resistant cables are a more reliable solution.

Learn about ATEX/IECEx-certified electrical cables for hazardous areas