In industries ranging from robotics to automotive to consumer electronics, flexibility is a crucial attribute of modern cable assemblies. Flexible cables enable compact routing, support dynamic motion, and enhance durability in challenging environments.
Achieving this flexibility requires careful consideration of materials, construction, and design. Coiled cables, in particular, offer a unique solution, combining durability and adaptability to meet the demands of various applications.
What Does Flexibility Mean for Custom Cable Assemblies?
Flexibility in cable assemblies refers to their ability to bend, twist, or stretch without compromising electrical performance or structural integrity. This property is vital in applications where cables are subject to constant motion or tight routing, such as inside compact electronic devices or dynamic mechanical systems.
In electronic enclosures, for example, cables often need to snake through tight spaces without causing stress on internal components. Similarly, battery packs depend on flexible cables to connect components efficiently within confined spaces. These examples highlight how flexibility enables innovation across diverse industries. A truly flexible cable ensures longevity and reliability, even under the harshest conditions.
Cable assembly routed in an enclosure.
Flexible Cable Jacket Materials
The choice of jacket material is one of the most critical factors in achieving flexibility. Standard UL-rated PVC is flexible, but this is a relative term. There are cable jacket options available that are more flexible than PVC. By means of additional processes, PVC cables can become more flexible by modifying the composition of the thermoplastic. Adding plasticizers will increase flexibility for standard PVC cables, but this could then cause the cable to lose its flammability rating.
Another option is semi-rigid PVC, for instance. This offers a balance between cost-effectiveness and moderate flexibility making it ideal for commercial applications. Silicone, known for its exceptional elasticity and resistance to high temperatures, is often used in medical applications that need a highly flexible solution. For applications requiring chemical resistance and rugged durability, TPE (thermoplastic elastomer) is a top choice. PTFE, on the other hand, stands out for its ability to endure extreme temperatures and exceptional dielectric properties, making it indispensable in aerospace and RF applications. Each material brings its own strengths, allowing engineers to select the most suitable option for their specific needs:
- PVC (Polyvinyl Chloride) – Standard readily available; low-cost
- SRPVC (Semi-Rigid Polyvinyl Chloride) – Flexible and low-cost
- Silicone (Siloxane) – Specialty with excellent flexibility
- TPE (Thermoplastic Elastomer) – Rubber-like, tough and flexible
- PTFE (Polytetrafluoroethylene) – Teflon, flexible with RF properties
Other Methods to Improve Cable Flexibility
While the most obvious way to modify the flexibility of a cable is to modify the jacket material, there are several other ways to improve the overall flexibility of a cable. Adjusting the strand count is the next best way to improve flexibility. A solid core center conductor is the least flexible wire type, and as the strand count increases, so does cable flexibility. Highly flexible wires can be made of several hundred fine strands of tinned copper wire.
Highly flexible multiconductor cable with high-strand count wire.
Simply reducing the wire gauge is another way to improve flexibility. There are applications where both a 26AWG and 28AWG wire will work and if flexibility is a concern, the 28AWG wire should be chosen.
Changing the shape of the wire cross-section is another option to further improve the flexibility of your wire. Cables with non-symmetric cross-sections can help solve unique design challenges. If your design application needs a 40+ conductor cable and a minimum bend radius of one inch, there are a few options that can meet this. A ribbon cable is an option to consider and is a flat flexible cable made of laminated wires within the same plane. Ribbon and flat cables can be routed in ultra-tight areas because of their shape.
Flat ribbon cable formed into shape.
Understanding Minimum Bend Radius
The minimum bend radius is a crucial design consideration for flexible cables, representing the smallest curve a cable can bend without risking damage. Exceeding this radius can lead to serious issues, such as broken conductors, compromised insulation, or signal degradation. The bend radius depends on several factors, including the conductor type, insulation material, and overall cable construction. By respecting this limitation during installation and use, manufacturers and end-users can ensure optimal performance and longevity of the cable assembly.
While this number should be viewed as an estimate or a rule of thumb, this represents the industry standard way to characterize flexibility. The minimum bend radius is usually calculated as multiple of the wire outer diameter and is usually 5x to 10x the wire diameter.
What Is a Coiled Cord?
One type of highly flexible cable is a permanently coiled cable, where the coil is set into the wire jacket material during production. A coiled cord, sometimes referred to as a retractable cable, is specifically designed to extend and retract without tangling or overstretching. This type of cable is widely used in scenarios where space efficiency and mobility are paramount. Devices like telephones and electric guitar cables often incorporate coiled cords to allow freedom of movement while maintaining a neat and organized appearance. Medical equipment provides reliable connections for devices that require frequent repositioning.
Coiled cords are formed using heat and pressure to permanently set the material in the coiled shape. This process of transforming a straight cable into a coiled one first involves selecting the right materials, typically wire jackets made from TPE or silicone are most preferred. These materials are best suited since they can withstand repeated stretching and recoiling. The bulk cable is then wound around a mandrel, a cylindrical tool that shapes the cable into its coiled form. Just like a perm from the 1980s, heat is applied to set the coil, and once the cable is cooled, it retains its shape permanently.
Example of a coiled cable assembly.
As directed by the end customer, the finished coiled cable undergoes rigorous testing to ensure it meets performance standards, including durability, extension cycles, and overall length. Over time, the coils can lose shape as they become stretched and worn out.
Summary
The craft of coiled cable assemblies is a testament to engineering innovation, blending advanced materials and manufacturing techniques to deliver cables that meet the demands of modern applications. Whether in robotics, automotive systems, or electronic devices, flexible and coiled cables offer unparalleled performance and durability. By understanding the principles behind flexibility, such as material selection, minimum bend radius, and manufacturing processes, engineers can design solutions that thrive in even the most challenging environments.
If you’re ready to explore how flexible and coiled cables can enhance your project, contact us today. Our team specializes in creating custom cable assemblies tailored to your specific needs, ensuring flexibility and reliability in every design.
