Multiconductor cables are among the most common types of wire harnesses used today for their high reliability and versatility. They are highly sought after because manufacturers can completely customize the wire cross-section, serving all industries and applications. Multiconductor cables are used everywhere, including USB cables, automotive harnesses, printer cables, electrical vehicle charging stations, x-ray machines, and so on.
But, hidden within the smooth gray or black outer jacket are various items that are not visible to the individual using the cable. These items aren’t necessarily used to electrically connect point A to point B but are used for several different purposes. These internal items include load-bearing members that help improve tensile strength, space filler materials that fill internal voids, creating a uniform diameter, or tubing that serves pneumatic purposes.
Lastly, electrically conductive items such as drain wires are included within the bundle to help shield the cable from unwanted electrical interference.
Example of a multiconductor cable with a drain wire.
How Are Multiconductor Cables Manufactured?
Multiconductor cables are built in several steps, with each manufacturing process designed to ensure the final product performs reliably in its intended environment. From conductor selection to shielding and final testing, the extrusion process brings together both electrical and mechanical design elements to meet custom application needs.
1. Conductor Preparation
The process begins with choosing the center conductors. These are typically copper (either solid or stranded), depending on the flexibility and current-carrying requirements.
Each conductor is extruded with a molten thermoplastic and insulated using materials like PVC, polyethylene (PE), or Teflon (PTFE). These materials are electrical insulators and help prevent short circuits while protecting against the environment. Color-coding or striping of the jacket is also applied during this step to aid in identification during assembly.
2. Core Assembly
This is where the “multi” in multiconductor cable comes to life. Conductors (individually or as twisted pairs) are laid together helically to form the cable core.
To support the mechanical structure:
- Fillers like cotton, foam rods, and other filaments are added to eliminate internal gaps and maintain a consistent cable diameter.
- Strength members such as Kevlar or aramid fibers may be included to enhance pull resistance.
- In hybrid designs, pneumatic tubes or other non-electrical elements like hoses may be added for additional functionality.
An example of a multiconductor cable with a filler members added.
The resultant multiconductor cable bundle is referred to as a core that is then mechanically bound and ready for shielding.
3. Shielding
Shielding is added to block out unwanted external electrical interference and protect the signal integrity of the conductors inside.
- Metalized foil wraps offer a lightweight and 100% coverage shield.
- Braided shields made of tinned copper provide excellent EMI protection, mechanical strength, and can help protect the cable bundle.
- A drain wire is typically included alongside a foil shield to offer a simple termination point and reference the shield to ground.
Shielding may be applied around individual sections (like twisted pairs) or over the entire cable core, depending on the application.
4. Jacket Extrusion
Once the internal components are in place, the cable is passed through an extrusion line where the outer jacket is applied.
This jacket serves as the first line of defense against abrasion, moisture, chemicals, and extreme temperatures.
- Common jacket materials include PVC, TPU, TPE, and silicone options.
- Jacket color, texture, and surface printing (like part numbers or logos) can be customized during this step.
5. Cooling, Cutting, and Testing
After extrusion, the cable is cooled and cut to length. It then goes through several quality checks:
- Spark test helps verify there are no exposed conductors along the wire jacket using a high-voltage screening process.
- Continuity testing ensures every conductor is connected end-to-end.
- Insulation resistance and hi-pot testing verify that the cable can withstand the rated voltage without breakdown.
- Mechanical tests may include pull strength, bend radius, and flex life evaluations to confirm durability.
What Are Filler Materials in Electrical Cables and Why Are They Used?
Filler materials are non-conductive components placed between the insulated conductors of a cable. Their primary function isn’t electrical. They’re used to maintain the cable’s shape, improve flexibility, enhance durability, and support overall structural integrity. Without fillers, cables with multiple conductors would be prone to irregular shapes, internal movement, or premature wear.
When properly selected, filler materials can help the cable resist kinking, twisting, or collapsing under mechanical stress. In some cases, fillers also provide additional protection from moisture, abrasion, or chemical exposure.
Below are some of the most common filler materials used in multiconductor cable construction:
Nylon
Nylon fillers are tough, lightweight, and resist chemicals and abrasion. They’re often used in ruggedized cables where added mechanical strength is needed. Nylon also has good flexibility, which helps maintain ease of installation without compromising structure.
Kevlar
Kevlar is a high-strength aramid fiber known for its extreme tensile strength. While not a true “filler” in the traditional sense, it’s often included alongside or instead of fillers to serve as a strength member. Kevlar is ideal in applications where the cable will be subjected to pulling or flexing, such as in medical devices or industrial robotics.
Yarn
Polyester or nylon yarn can be used as filler to help round out the cable geometry and improve flexibility. Serving as a low-cost option, yarn also adds minimal weight and can absorb some mechanical stress without affecting electrical performance.
PTFE
Polytetrafluoroethylene (PTFE), also known by the brand name Teflon, is a high-performance plastic filler used in high-temperature or chemically aggressive environments. It’s non-stick, heat-resistant, and has very low friction, making it useful for specialty applications like aerospace or military-grade cables.
Paper
Paper is a cost-effective filler commonly found in lower-voltage or static applications. It helps fill voids, maintain shape, and insulates between conductors, but it’s less durable in environments with moisture or high movement.
Cotton
Cotton is a traditional filler material that provides softness and flexibility. It’s still used in some cable designs where pliability is important. Cotton can also help absorb small amounts of moisture, though it’s not ideal in wet or harsh environments without added treatment.
Various Types of Tape
Filler tapes, such as Mylar, polyester, or non-woven fabrics, are wrapped around conductors or used between conductor layers. Tapes can serve dual purposes: filling space and adding separation or insulation layers. In some cases, water-blocking tapes are used to help resist moisture ingress.
What Are Vent Tubes and Why Are They Added to Multiconductor Cables?
A vent tube is a hollow, non-electrical component embedded within a multiconductor cable that allows air or gas to move freely through a sealed system. While not required for every application, vent tubes offer a simple, low-cost solution for managing pressure differentials in enclosed electronics, particularly where sensitive components are at risk due to changes in altitude, temperature, or humidity.
Why Use a Vent Tube?
In sealed enclosures, internal pressure can build up due to environmental changes or heat generated during operation. Without proper venting, this pressure can:
- Stress seals and gaskets
- Compromise moisture barriers
- Disrupt sensor readings or optical components
- Lead to premature failure of electronics
Example of a multiconductor cable with a vent tube.
By including a vent tube directly within the cable design, engineers eliminate the need for separate venting systems or additional enclosure modifications. The result is a streamlined, integrated solution that reduces assembly complexity and potential leak paths.
Design Flexibility with Strength Members and Tubing
Multiconductor cables with integrated vent tubes or strength members are highly customizable. Engineers can specify:
- Filament or tube diameter and material
- Cable jacket types (PVC, TPE, FEP, etc.)
- Wire gauges, shielding options, and color coding
- UL-rated configurations for regulatory compliance
Choosing to embed a vent tube or a strength member into the cable not only saves space but also enhances long-term reliability. For projects that require this kind of functionality, it’s a clean, efficient design choice.
Summary
As with any custom cable assembly, early involvement with a knowledgeable supplier, one experienced in unique cable designs, can significantly reduce development time and cost. Engaging Epec’s engineering team during the early design phase ensures the final product meets both mechanical and environmental requirements without unnecessary revision cycles.
Key Takeaways
- Multiconductor Cables Are Fully Customizable for Strength and Functionality: Beyond just carrying signals, modern multiconductor cables often include strength members, filler materials, vent tubes, and shielding to improve durability, manage pressure, and maintain signal integrity in harsh environments.
- Filler Materials Improve Structure and Flexibility: Fillers such as nylon, yarn, Kevlar, and PTFE help maintain cable shape, prevent internal movement, and enhance mechanical performance, particularly in flexible or high-stress applications.
- Vent Tubes Help Manage Pressure in Sealed Electronics: Embedded vent tubes allow air or gas to flow through enclosed systems, preventing pressure build-up that could damage seals, gaskets, or sensitive electronics, especially in altitude- or temperature-sensitive environments.
- Shielding Preserves Signal Quality and EMI Protection: Options like foil wraps, braided shields, and drain wires are used to block electrical noise and ensure reliable performance, especially critical for data transmission or medical applications.
- Design Collaboration with Your Supplier Saves Time and Cost: Working with an experienced cable manufacturer during the early design phase ensures the correct selection of materials and components, minimizing rework and accelerating time to production.
