When it comes to designing custom cable assemblies, understanding the specific requirements is critical. These assemblies are not just a collection of wires, they are key components of complex systems where safety and reliability are non-negotiable.
Every detail, from power requirements to environmental conditions, plays a role in how the cable will perform in its intended application. Whether it’s for industrial machinery, medical devices, or aerospace systems, properly designed cables ensure that the systems they support function safely and efficiently.
This bundle of power and adapter cables highlights the variety of connectors used in custom assemblies, each designed to handle different voltage, current, and device compatibility needs.
Importance of Understanding Power Requirements
One of the most important steps of the cable assembly design process is understanding the power requirements. Without taking these requirements into account, the safety and efficacy of the final product can suffer. Whether you are designing a simple two-lead cable or a pigtail cable with multiple terminations, they must meet specific voltage and current requirements while accounting for environmental conditions.
The design of the cable will be greatly affected based on the voltage and current requirements of the system. In a simple electrical system, these requirements are usually less important, but when dealing with more complex or higher power systems, it’s a critical consideration.
Voltage
Voltage is the electrical potential difference between two reference points within a circuit. When considering how much voltage potential is across the conductors in a cable, the designer will often choose between different insulation materials and different insulation thicknesses. If the insulation is not sufficient to handle the voltage requirements, then it can lead to breakdown, arcing, and short-circuiting. Higher voltage applications will typically use higher-grade insulation material such as Teflon or Polyethylene, which offer much higher dielectric constants in comparison to cheaper PVC-insulated wire jackets.
Current
Current is the flow of electrical charge going through the cable while energized and plays a more crucial role in the design than the voltage of the cables. If the current capability of a cable is exceeded, it can lead to overheating, insulation melting, and even catastrophic failures like fire.
When considering how much current will be flowing through a conductor in a cable, designers will mostly focus on the wire gauge and conductor materials. In electronics, it’s common to compare the flow of electricity in a wire to the flow of water in a pipe. Analogous to current, to accommodate a higher flow of water, you will need to increase the diameter of the pipe. If you need to accommodate a higher flow of electricity, you will need a higher diameter of wire. The same principle applies to the conductor’s material as well. Typically, wires are made from copper which has low electrical resistance. Sometimes other materials such as aluminum for weight savings or steel for its mechanical strengths are used. These materials are less conductive than copper and will require a wider diameter conductor to transmit the same amount of current.
Environmental Factors in Cable Design
In addition to the power requirements like voltage and current, the environment that the cable will be operating in will significantly influence the design as well. Factors such as temperature, exposure to chemicals, mechanical stress, and electromagnetic interference need to be accounted for.
Mechanical and environmental conditions will all influence the jacket material that is selected for cable design. If the end use of the cable is in a harsh environment with exposure to chemicals, oils, or corrosive substances, a material such as Polyurethane or Teflon could be used; they have higher resistance to harsh chemicals and oils.
These materials would also be suitable for high mechanical stress applications in abrasive environments. If the cable is going to be used in a high-temperature environment, materials such as Silicone or Teflon can be considered which are able to withstand higher temperatures than a PVC or Polyethylene wire jacket.
Shielding for Electromagnetic Interference
Shielding is another critical design consideration, especially when dealing with electromagnetic interference (EMI). EMI can cause disruptions in signal integrity, leading to malfunctions or degraded performance in sensitive equipment. Designers use different shielding techniques to protect cables from external electromagnetic fields. Braided wire shields are one option and are highly effective for guarding against low-frequency EMI. They’re also flexible, making them a good choice for cables that need to move or flex during use.
Foil shields are another option, better suited for high-frequency interference, though they’re less durable for applications that involve repeated motion or bending. The type of shielding needed often depends on the environment where the cable will be used. For example, cables in industrial or medical settings often need stronger shielding to prevent interference from motors, power lines, or wireless transmitters.
This cutaway view of a multi-conductor shielded cable shows the intricate layering of wires, insulation, and shielding, designed to protect signals from interference while ensuring durability in demanding environments.
Connectors and Termination Techniques
Connectors and termination techniques are equally important. Choosing the right connectors not only ensures functionality but also impacts how durable and user-friendly the cable assembly will be. The type of connector used depends on factors like pin count, current capacity, and how many times the cable will need to be connected and disconnected during its lifetime. High-power applications require connectors with robust contacts to handle higher currents safely.
Meanwhile, data cables often focus more on maintaining signal integrity. Termination methods, whether crimping, soldering, or insulation displacement, also vary depending on the requirements of the application. Crimping is widely used because it’s fast and reliable, especially in mass production, but soldering is often preferred when a more permanent connection is needed. In environments with high vibration, adding strain reliefs or potting materials can help prevent terminations from failing over time.
Here’s a look at a simple power inlet cable assembly with pre-attached wiring—showing how connectors and terminations come together to make installation easier and more reliable in custom cable designs.
Compliance with Standards and Certifications
Cables used in specialized industries often need to meet strict standards and certifications. For example, UL certifications ensure that cables meet specific safety benchmarks like fire resistance and insulation performance. RoHS compliance is another key requirement, particularly for environmentally friendly designs, as it ensures that hazardous materials like lead and mercury are not used. Industry-specific certifications also come into play. Medical cables might need to meet biocompatibility and sterilization standards, while aerospace cables have to withstand extreme conditions and comply with stringent regulations.
Once the design is finalized, testing and validation are critical steps to ensure the cable assembly meets all performance requirements. Electrical tests like continuity and insulation resistance help confirm that the cable will operate as intended, while mechanical tests like flex and tensile testing verify the cable’s ability to endure physical stresses. Environmental tests are also important for cables designed for challenging conditions. For instance, cables intended for outdoor use might undergo UV resistance and water ingress tests, while high-temperature cables are tested to ensure they can withstand thermal cycling. Testing isn’t just a one-time process either. In some industries, ongoing quality control through batch testing or certification audits is required to maintain reliability.
Summary
Properly designed custom cable assemblies are more than just a way to connect components, they’re an essential part of ensuring that systems run safely and reliably. Taking the time to consider power requirements, environmental factors, shielding, connectors, and compliance standards upfront can make all the difference.
By thoroughly testing and validating the final design, you can be confident that the cable will perform as expected, even in the most demanding applications. Investing in a well-designed cable assembly means investing in the success and safety of the entire system.
Key Takeaways
- Critical Role of Cable Assemblies: Custom cable assemblies are integral to complex systems, ensuring safety, reliability, and efficient operation in industries such as medical, industrial, and aerospace.
- Importance of Power Requirements:
- Voltage Considerations: Proper insulation material and thickness are essential to prevent breakdown, arcing, and short circuits in high-voltage applications.
- Current Considerations: Wire gauge and conductor material determine the cable’s ability to handle current without overheating or failing. Copper is preferred for its low resistance, but aluminum and steel can be used for weight savings or mechanical strength.
- Environmental Factors: The operating environment significantly impacts cable design:
- Temperature Resistance: Materials like Teflon and Silicone are suitable for high temperatures.
- Chemical and Mechanical Resistance: Polyurethane and Teflon excel in harsh environments with exposure to oils, chemicals, or abrasion.
- EMI Shielding: Shielding is crucial for maintaining signal integrity:
- Braided Wire Shields: Effective for low-frequency EMI and flexible applications.
- Foil Shields: Better for high-frequency interference but less durable under repeated motion.
- Connectors and Termination Techniques:
- Connector Selection: Based on pin count, current capacity, and durability needs.
- Termination Methods: Crimping is fast and reliable for mass production, while soldering offers more permanent connections. Strain reliefs or potting materials can improve durability in high-vibration environments.
- Compliance with Standards and Certifications:
- Industry Certifications: UL, RoHS, and application-specific standards (e.g., biocompatibility for medical cables, extreme condition requirements for aerospace).
- Ensures safety, environmental compliance, and performance reliability.
- Testing and Validation: Thorough testing ensures cables meet performance and durability requirements:
- Electrical Tests: Verify continuity and insulation resistance.
- Mechanical Tests: Confirm the ability to withstand flex, tensile stress, and environmental challenges like UV exposure and water ingress.
- Investing in Proper Design: Comprehensive planning for power, environment, shielding, and compliance ensures the cable assembly supports system performance and longevity, minimizing risks and failures.
