Introduction to Cable Assemblies
A cable assembly, also known as a wiring harness or cable harness, is a group of cables and connectors that are assembled together to transmit signals or electrical power. Cable assemblies provide interconnectivity solutions and play a vital role in many industries such as automotive, aerospace, industrial automation, medical devices etc. They are commonly used to connect sub-systems and components efficiently while streamlining system design and installation.
What is a Cable Assembly Made Of?
A cable assembly consists of the following components:
- Cables: Insulated wires that transmit signals or power. Common types are coaxial cables, shielded and unshielded twisted pair cables, ribbon cables, fiber optic cables etc.
- Connectors: Mounted at the ends of cables to enable connection. Popular connector types are circular, rectangular, D-type, USB, RJ45 etc.
- Terminals: Attached to the stripped ends of cables to facilitate connection. Screw terminal blocks, crimp terminals and solder terminals are some examples.
- Conduits: Tubing used to bundle and route the cables together. Braided sleeving and spiral wrapping are commonly used.
- Strain Reliefs: Placed where cables enter a connector body to protect against cable damage due to tension or bending.
- Shielding: Braiding or foil wrapping around cables and connectors to prevent EMI/RFI interference.
- Insulation: Plastic jacketing material around cables for insulation against current leakage or environmental factors. Common materials used are PVC, Teflon, polyethylene etc.
Benefits of Using a Cable Assembly
- Simplified Installation: Pre-assembled cables allow faster and easier system installation.
- Cost Savings: Lower assembly costs compared to labor-intensive onsite cable fabrication and termination.
- Reliability: Factory assembly ensures cables are fabricated and tested to meet quality standards.
- Customization: Tailor-made assemblies match the specific cable and connector requirements.
- Space Optimization: Integrated assemblies minimize space requirements and clutter.
- Troubleshooting: Pre-tested assemblies facilitate faster troubleshooting and fault isolation.
Cable Assembly Design Considerations
Designing an optimal cable assembly requires careful consideration of many parameters:
Cable Type
- Choose cable configuration (single, multi-conductor), gauge, insulation material etc. based on electrical performance needs and environment.
Connectors
- Select compatible high-quality connectors to match cable type and system interfaces.
Circuit Configuration
- Plan conductor grouping, shielding, and grounding paths based on circuit logic and noise susceptibility.
Length
- Determine required cable lengths for equipment placement and allow extra slack if systems are movable.
Strain Relief
- Include adequate strain relief and cable clamps for long cable runs or applications involving motion/vibration.
Shielding
- Incorporate braided or foil shields to prevent EMI/RFI noise if required by environment.
Heat Dissipation
- Use cables and insulation with adequate current rating and heat tolerance for power transmission.
Environmental Factors
- Consider chemical resistance, UV/sunlight resistance, waterproofing needs etc. based on operating environment.
Routing
- Plan routing paths to avoid sharp bends, hazards and accommodate equipment access needs.
Standards Compliance
- Adhere to application-specific standards for industrial, military, aerospace, automotive etc. cable assemblies.
Cable Assembly Manufacturing Process
Constructing a cable assembly involves several key stages:
1. Design and Engineering
- System interfaces and requirements are evaluated to design schematics specifying required cable types, connectors, pin assignments etc.
- Cable/harness design software assists in optimizing wire gauge, lengths, and efficient routing.
- Structural elements like conduits and shields are incorporated into the assembly design.
- Prototypes may be built for design verification and testing.
2. Kitting and Cutting
- Sourced components like cables, connectors, and terminals are organized into assembly kits per bill of materials.
- Cables are cut precisely to required lengths using specialized cutting tools.
3. Connector Assembly
- Connectors are attached to cable ends by soldering, crimping, or insulation displacement.
- Contact insertion tools ensure proper pin alignment.
- Connector shells are assembled and back shells are secured.
4. Cable Marking and Terminations
- Cables are marked or labeled for identification during installation.
- Stripped cable ends are terminated with solder cups, crimp terminals etc.
5. Cable Bundling and Routing
- Cables are bundled using ties, sleeves or conduit for organization and protection.
- Routing paths are laid out to avoid tight bends and accommodate equipment.
6. Strain Relief and Shielding
- Strain relief fittings are mounted at cable entry and exit points.
- Shielding like copper braids are woven around cable bundles for noise immunity.
7. Quality Inspection and Testing
- Visual examination checks for defects in materials, terminations, or shielding.
- Continuity testing verifies all electrical connections have integrity.
- Samples may undergo mechanical stress tests for durability.
8. Delivery Preparation
- Completed cable assemblies are tagged and packed for shipment.
- Certifications of compliance and test reports are provided.
Cable Assembly Tools and Equipment
Specialized tools are required to fabricate and test custom cable assemblies:
Wire Processing Tools
- Cable cutters – For precise cutting of wires to required lengths.
- Wire strippers – For stripping insulation off cable ends for termination.
- Crimping tools – For crimping terminals, pins or splices onto stripped wire ends.
Connector Tools
- Insertion/extraction tools – For inserting contacts into connector housings or removing them.
- Crimping pliers – For crimping contacts onto cable ends.
- Soldering irons – For soldering cable wires to connector contacts.
- Hex crimp tools – For securing back shells onto connector plugs.
Cable Marking and Terminating
- Cable labeling machines – For printing identifying numbers and markers onto cable jacketing.
- Heat guns – For heating and shrinking labels, shrink tubing.
- Cable lacing needles – For bundling and lacing wire harnesses.
Testing Equipment
- Multimeters – For verifying continuity across cables and connectors.
- Hipot testers – For performing high potential (hi-pot) dielectric tests.
- Network/protocol analyzers – For exercising assembly interfaces and verifying communication.
Assembly Aids
- Cable racks and boards – For routing bundles neatly during assembly.
- Cable pullers – For pulling cables through conduits during harness fabrication.
Challenges with Cable Assemblies
Some common challenges encountered with cable assemblies include:
- Complex routing – For intricate wiring configurations and tight spaces. Requires planning of bend radii, cable retention.
- RF interference – Cables can emit and receive electromagnetic interference. Needs shielded cables or grounded metal conduit.
- Power limitations – Cable gauges and insulation must match ampacity ratings. Higher loads need larger wire sizes.
- Strain relief – Moving applications require well-anchored strain relief fittings to avoid broken wires.
- Size and weight – Large wire bundles get stiff, heavy and occupy considerable space. Needs careful routing and clamps.
- Maintenance – Repairing faulty assemblies is difficult. Modular connectors and quick disconnects improve serviceability.
- Material aging – Plastics and insulators can crack over time. Environmental sealing is required in some cases.
- Miswiring – Incorrect assembly can damage systems. Rigorous quality checks and tooling fixtures prevent errors.
- EMC compliance – Shielding, grounding and filtering needed for meeting emission and immunity standards.
Cable Assembly Applications
Cable assemblies are ubiquitous and find usage in an enormous range of applications:
Computing and Networking Equipment
Internal cabling for signal routing in servers, PCs, switches, routers etc. Flexible flat cables connect drives and boards.
Automotive Wiring
Power and signal distribution harnesses for vehicle electrical systems and electronics.
Medical Equipment
Patient monitoring systems, imaging machines etc. use specialized shielded cables to preserve signal integrity.
Industrial Control Systems
Connectivity solutions for robotics, motor drives, control panels, machine wiring. Highly ruggedized assemblies.
Aerospace and Military
Mission-critical cabling for avionics, communications, weapon systems. Rigorous testing and screening.
Consumer Electronics
Shorter cable assemblies inside home/office appliances, instruments, gadgets. Flexible wires with small connectors.
Power Transmission and Distribution
Heavier gauge wiring for electrical utilities, power plants and grid infrastructure.
Instrumentation and Control
Sensor cabling, signal conditioning wiring, process control loop connections.
Best Practices for Cable Assembly Design
Here are some proven techniques for optimizing the design of reliable and high-performance cable assemblies:
- Assign each cable and wire with a unique identifier for easy troubleshooting.
- Include service loops when routing to allow repositioning during use.
- Avoid aggressive bends with tight radii which can damage cables.
- Minimize overall harness length to reduce size, weight and transmission loss.
- Route cables neatly in bundles using sleeves, carriers or conduits.
- Provide adequate strain relief and anchoring for cables entering connectors.
- Group same signal type wires together and separate from noisy power lines.
- Utilize shielded cables or grounded conduits when wiring sensitive analog signals.
- Use connectors with positive locking features to prevent vibration loosening.
- Specify connector backshells and boots to protect contacts from corrosion and moisture.
- Place connectors requiring manipulation on easily accessed panels.
- Include protective slack loops for cables connecting movable equipment.
- Review harness drawings carefully for errors before production.
- Perform quality inspection and continuity testing on all assemblies before shipment.
How to Select the Right Cable Assembly Manufacturer?
Choosing the ideal partner for outsourcing cable assembly production involves evaluating several key factors:
- Industry Experience – Domain expertise for application-specific requirements and standards compliance.
- Quality Processes – Consistent quality assurance during production and testing. ISO certification is preferable.
- Technical Capabilities – State-of-the-art fabrication and test equipment for high-mix needs.
- Materials Sourcing – Vetted supply channels for cables, connectors, components.
- Customization Skills – Ability to collaborate on custom designs and rapid prototyping.
- Value-Added Services – Assistance with design, documentation, testing, logistics.
- Cost Competitiveness – Reasonable pricing models and minimum order quantities.
- Manufacturing Scale – Capacity for high-volume production and quick turnarounds.
- Customer Support – Responsiveness to technical queries and post-sales assistance.
- Proximity – Nearest location for ease of interactions and logistics.
By carefully evaluating partners against these criteria, product developers can select the right cable assembly producer to meet program needs in a timely and cost-effective fashion.
FAQ
What’s the difference between a cable assembly and a wiring harness?
A wiring harness bundles multiple wires into a single integrated assembly, while a cable assembly is a harness that incorporates connectors at one or both ends. So a cable assembly can be considered a type of wiring harness.
What are the different kinds of cables used in assemblies?
Common cable types include multi-conductor round cables, ribbon cables, coaxial cables, twisted pair cables, fiber optic cables, shielded cables etc. Choice depends on factors like signal types, electrical properties, environment etc.
How are strain reliefs added to cable assemblies?
Strain relief fittings grip the cable jacket and prevent pull force from damaging wire terminations. They are installed using adhesives, ties, clamps or overmolding where cables enter connector bodies.
What are some best practices for grounding cable shields?
Cable shield grounding should be done at only one end to avoid ground loops. Use 360° grounding connectors with shining teeth for optimal contact. Ground to chassis directly or through ground plane.
How can EMI/RFI interference be minimized in cable assemblies?
Shielded cables, metal conduit, ferrite chokes, grounding and physical separation from noise sources help reduce interference. Twisting wire pairs also maintains balance.
What are some key tests performed on cable assemblies?
Typical quality assurance tests include continuity verification, insulation resistance measurement, high voltage withstand testing, and functional/communication validation. Environmental tests involve vibration, flexing, temperature cycling.
How are aerospace cable assemblies different from commercial assemblies?
Aerospace assemblies use approved components and undergo more rigorous qualification and lot testing. Cables are usually Teflon insulated. Shielding and redundancy levels are higher.
What materials provide maximum chemical resistance for cable jackets?
For extreme chemical environments, cables with Tefzel or Teflon jackets are best. Thermoset jackets like cross-linked polyethylene also offer broad chemical resistance.
How can cable assemblies be made waterproof?
Techniques like sealed connectors with o-rings, gel infilling open connectors, composite tubing or enclosures, and water-blocking cable jackets help exclude water ingress.
