How to Specify a Custom Cable Assembly for OEM Projects

How to Specify a Custom Cable Assembly for OEM Projects

For OEM projects, a cable assembly is rarely just a cable with connectors attached. The assembly may need to fit a limited installation space, meet specific electrical requirements, withstand repeated movement, and remain consistent from prototype to mass production.

This is why specifying a custom cable assembly at the beginning of a project is important. A cable that looks suitable on paper may still create problems during assembly, signal transmission, mechanical testing, or production.

A good specification gives the cable assembly manufacturer enough information to evaluate the application, select suitable materials, identify potential design issues, and develop a solution that can move from prototype to production.

What Should an OEM Specify Before Requesting a Custom Cable Assembly?

Direct Answer

A custom cable assembly specification should describe how the assembly will function inside the finished product, rather than only identifying a cable type or connector.

The most useful information normally covers:

Application → Signal Requirements → Cable Construction → Connector → Mechanical Requirements → Environment → Testing → Production

If → the OEM already has a complete drawing and defined electrical requirements

Then → provide the drawing, BOM, connector part numbers, pinout, cable dimensions, electrical requirements and applicable testing criteria

Why → the manufacturer can evaluate the design against both assembly feasibility and production requirements.

If → the OEM does not yet have a complete cable specification

Then → provide the application, interface, available installation space, signal type, cable length and connector information that is already known

Why → these inputs can give the supplier enough information to begin engineering review before every cable parameter has been finalized.

If → the cable assembly will move from prototype to mass production

Then → specify expected production volume, inspection requirements, documentation and qualification expectations early

Why → a design that works for a small prototype quantity may require different tooling and process controls for volume manufacturing.

The current HOTTEN article already follows this general structure and emphasizes that custom cable projects should consider application, electrical performance, mechanics, connectors, environment and production from the beginning.

What Information Should Be Included in a Custom Cable Assembly Specification?

A practical OEM cable assembly specification should normally cover six areas:

Not every project requires every parameter. The important point is to identify the requirements that can affect cable design and assembly performance.

1. Start With the Application, Not Just the Cable Type

One of the most common mistakes in cable sourcing is starting with a product name instead of the actual application.

For example, an OEM may request a "flexible coaxial cable" without specifying how the cable will move, what frequency it will carry, or how it will be installed.

The same basic cable construction can behave very differently depending on the application.

A cable used inside a stationary electronic device may have very different requirements from one installed in a robotic joint, drone gimbal, or medical imaging probe.

Before selecting the cable, define:

• Where the cable will be installed

• What signal or power it will carry

• How often it will move

• How much installation space is available

• What temperature and environmental conditions it will experience

• How the cable will connect to the rest of the system

This application information gives the manufacturer a better starting point for cable selection and engineering review.

2. Define the Electrical Requirements

Electrical requirements should be specified according to the actual system interface.

For high-frequency coaxial cable assemblies, common parameters include:

• Characteristic impedance

• Operating frequency

• Insertion loss or attenuation

• Return loss

• Shielding requirements

• Capacitance

• Maximum voltage, where applicable

For example, a 50 Ω coaxial assembly may be required for an RF system, while other interfaces may use different impedance requirements.

For differential interfaces such as LVDS, the specification may include a target differential impedance and electrical-length matching requirement.

The important point is that impedance should not be specified independently from the complete signal path. The cable, connector, termination, PCB transition, and receiving device can all contribute to signal discontinuities.

What if the OEM does not know the required cable specifications?

This is common during early-stage development.

In that situation, the OEM can provide the interface information and application requirements instead of attempting to define every cable parameter independently.

A cable assembly manufacturer can then review factors such as:

• Signal type

• Frequency or data rate

• Interface

• Cable length

• Connector configuration

• Space limitations

• Flexibility requirements

The manufacturer can use this information to recommend a suitable cable construction and identify parameters that should be verified during prototyping.

3. Specify the Mechanical Requirements

Electrical performance is only one part of cable assembly design.

For moving equipment, mechanical requirements can be equally important.

A custom cable assembly may need to withstand:

• Repeated bending

• Torsion

• Vibration

• Pulling

• Routing around tight corners

• Connector movement

• Repeated insertion and removal

For robotic and gimbal applications, for example, the cable may move continuously while the equipment is operating.

In medical equipment, the cable may also need to maintain flexibility while being exposed to cleaning or sterilization procedures, depending on the device design.

A useful specification should therefore include the expected movement and installation conditions rather than simply asking for a "flexible cable."

For example:

Required bend radius: application-specific
Movement: repeated bending and torsion
Installation: compact routing around moving mechanism

The manufacturer can then evaluate conductor construction, insulation, shielding, jacketing, and strain-relief design together.

4. Connector Selection Is Part of the Cable Design

Connectors should not be treated as an afterthought.

The connector affects:

• Available installation space

• Electrical transition

• Mechanical strength

• Mating reliability

• Cable routing

• Assembly cost

For high-frequency applications, the connector and cable transition can also introduce impedance discontinuities.

For compact electronics, connector size can become a major design constraint. In some applications, the cable itself may fit within the available space while the connector does not.

The specification should therefore include:

• Connector manufacturer and part number, if already selected

• Interface type

• Plug/receptacle configuration

• Number of connectors

• Connector orientation

• Keying or locking requirements

• Plating or material requirements, where relevant

If the connector has not yet been selected, providing the available installation dimensions can allow the cable assembly manufacturer to evaluate suitable options.

5. Consider Shielding as a Complete System

For signal cables used in RF, medical imaging, high-speed electronics, and other noise-sensitive applications, shielding requirements should be considered together with cable construction and termination.

Common shielding structures include:

• Metallic foil

• Braided shield

• Spiral shield

• Combined foil and braid structures

The appropriate structure depends on the application and frequency range.

Simply specifying a high percentage of braid coverage does not completely define shielding performance. Shield construction, grounding, connector termination, frequency, and system configuration can all affect electromagnetic performance.

For this reason, an OEM specification should describe the actual electromagnetic requirement where possible.

For example:

The cable assembly must provide adequate shielding for the specified operating frequency and system environment.

If a specific shielding test method or performance target is required, it should be included in the project specification.

6. Define Environmental Requirements Early

Environmental conditions can change the cable design significantly.

Important factors may include:

• Operating temperature

• Storage temperature

• Humidity

• Water or fluid exposure

• Chemical exposure

• UV exposure

• Vibration

• Sterilization

• Cleaning procedures

Medical devices are a good example.

An ultrasound probe cable may require a combination of flexibility, signal integrity, mechanical durability, and resistance to the cleaning or sterilization process used by the device.

Similarly, UAV and robotics cable assemblies may experience vibration, repeated movement, temperature changes, and compact routing.

Environmental requirements should therefore be specified before finalizing materials rather than added after the cable design has already been developed.

7. Tell the Manufacturer About the Production Stage

A cable assembly designed for ten prototypes does not necessarily have the same manufacturing considerations as one intended for long-term volume production.

An OEM should ideally indicate:

• Prototype quantity

• Expected production volume

• Target production timing

• Expected annual demand

• Required inspection

• Documentation requirements

• Packaging requirements

This allows the supplier to consider manufacturability from the beginning.

For example, a prototype may be assembled manually while a higher-volume project may require dedicated tooling, process controls, automated inspection, or a more standardized assembly process.

Discussing production requirements early can help avoid redesigning the cable when the project moves from engineering validation to mass production.

What Should OEMs Ask a Cable Assembly Manufacturer Before Prototyping?

Before placing a prototype order, OEM engineers can ask several practical questions:

Can you review the design before quotation?

A capable cable assembly supplier should be able to identify obvious manufacturing or assembly issues before production begins.

Can the proposed cable construction meet the electrical requirements?

The supplier should be able to explain the relationship between cable geometry, dielectric material, shielding, conductor construction, and the required electrical performance.

Can the design support repeated movement?

For flexible applications, the supplier should evaluate the complete assembly rather than focusing only on the cable itself.

Can the prototype design be transferred to production?

The prototype should ideally be designed with future manufacturing requirements in mind.

What testing will be performed?

Testing should be based on the project's actual requirements. Depending on the cable design, this may include dimensional inspection, continuity testing, electrical testing, impedance verification, tensile testing, or flex-life testing.

From Prototype to Production: Why Early Engineering Review Matters

The most effective custom cable projects usually involve engineering discussion before production rather than treating the cable as a standard purchased component.

During the early stage, the manufacturer can review:

Application → Cable Construction → Connector → Assembly → Testing → Production

This process helps identify potential conflicts between electrical, mechanical, and manufacturing requirements.

For example, reducing cable diameter may improve installation space but affect mechanical strength or electrical performance. Increasing shielding may improve electromagnetic protection but increase diameter and stiffness.

A custom cable assembly therefore requires balancing multiple requirements rather than optimizing a single specification.

How HOTTEN Supports Custom Cable Assembly Projects

HOTTEN focuses on customized cable and cable assembly solutions for applications where standard off-the-shelf cables may not meet the required combination of size, flexibility, electrical performance, and mechanical requirements.

Our capabilities cover applications including:

• Micro coaxial cable assemblies for compact and high-density electronic systems

• Medical cable assemblies for ultrasound, endoscopy, imaging, and other medical equipment

• UAV and drone cable assemblies for lightweight and moving platforms

• Robotics wire harnesses for systems with repeated movement

• RF coaxial cable assemblies for high-frequency signal applications

• Fine and ultra-fine electronic wire for compact electronic devices

For OEM projects, HOTTEN can support the process from application review and cable selection through prototyping, assembly, testing, and production.

The exact cable construction and inspection plan are defined according to the requirements of each project rather than applying one standard configuration to every application.

How Should OEM Engineers Build a Custom Cable Assembly Specification?

A useful OEM specification should move from the system requirement to the finished cable assembly.

A practical sequence is:

Application → Interface → Electrical → Mechanical → Connector → Environment → Testing → Production

This allows the supplier to determine which parameters are fixed, which can be optimized, and which need to be validated during prototype development.

1. Separate Customer Requirements From Supplier Design Variables

One of the first things an OEM should determine is:

Which specifications are already fixed, and which ones can the cable manufacturer optimize?

For example:

If → a parameter is dictated by the device architecture

Then → define it as a controlled customer requirement

Why → the supplier should not modify a system-level interface assumption without engineering approval.

If → a parameter is not yet fixed

Then → identify it as an engineering variable for DFM or supplier review

Why → this gives the manufacturer room to optimize manufacturability, performance and cost.

This distinction is particularly useful during early OEM development, when the application may be clear but the final cable construction is not.

2. Provide the Application Before Asking for a Standard Cable

The current article already makes an important point: starting with a cable name alone can be insufficient.

For example, “flexible coaxial cable” does not tell the supplier:

• where the cable is installed
• what signal it carries
• how frequently it moves
• what bend radius is available
• how long the finished assembly will be
• what connector is required
• what environmental conditions it will experience

If → the cable is used in a medical imaging probe

Then → provide probe space, channel count, signal characteristics, flexibility, connector and cleaning/sterilization requirements where applicable

Why → medical imaging cables often combine high-density electrical routing with mechanical movement and constrained installation.

If → the cable is installed in a drone gimbal or robotic mechanism

Then → provide movement type, bend radius, vibration conditions, cable routing and mass/space constraints

Why → dynamic applications impose different mechanical requirements from stationary electronics.

See the related [UAV & Robotics] resource and [Medical Equipment] resource on HOTTEN's site.

3. Define the Electrical Interface Before Selecting Cable Construction

A useful electrical specification may include:

If → the OEM knows the system data interface but not the exact cable construction

Then → specify the interface requirement instead of choosing the cable construction independently

Why → the cable manufacturer can evaluate conductor, dielectric, shielding and assembly structure against the system requirement.

The current article already notes that high-frequency assemblies may require impedance, frequency, insertion loss, return loss, shielding and capacitance, while LVDS-type interfaces may also require differential impedance and electrical-length matching.

4. Define Mechanical Requirements as Measurable Parameters

“Flexible” and “small” are not complete mechanical specifications.

A more useful RFQ can define:

If → the cable moves repeatedly

Then → define the movement profile instead of simply requesting a “high-flex cable”

Why → bend radius, cycle count, speed and torsion all affect mechanical loading.

If → the cable is installed in a fixed routing path

Then → provide the actual routing envelope and allowable bend radius

Why → installation geometry can affect the cable structure selected by the supplier.

This also creates a direct connection to the third article:

How Flex-Life Testing Helps Medical Cable Assemblies Maintain Performance After Repeated Bending

5. Treat Connector Information as Part of the Cable Specification

Connector information should be as specific as possible.

Useful information includes:

• manufacturer
• part number
• mating interface
• plug / receptacle
• number of connectors
• pin count
• pinout
• orientation
• keying
• locking mechanism
• plating requirement where applicable
• available connector space

If → the connector has already been selected

Then → provide the exact manufacturer part number and interface information

Why → cable termination and mechanical integration depend on the actual connector geometry.

If → the connector has not yet been selected

Then → provide the available installation space and interface constraints

Why → the supplier may be able to evaluate suitable connector options together with the cable design.

The current article already notes that the cable can fit mechanically while the connector does not, making connector selection an important early design decision.

6. Drawings, Samples, BOMs and Pinouts Have Different Engineering Value

OEMs often have different levels of documentation at different project stages.

If → the existing assembly is already working in a device

Then → provide a physical sample together with any known drawings or electrical requirements

Why → the supplier can evaluate both physical construction and functional requirements.

If → only a connector number is available

Then → provide the application and available mechanical/electrical information

Why → a connector part number by itself does not define the cable assembly.

7. Define What “Custom” Actually Means

A custom cable assembly can involve different levels of customization.

If → a standard connector and cable are already acceptable

Then → customization may focus on length, termination or assembly configuration

Why → not every OEM project requires a completely new cable construction.

If → the device requires unusual size, flexibility, shielding or electrical performance

Then → evaluate the complete cable architecture

Why → solving a single parameter may create a conflict elsewhere.

HOTTEN's current capabilities explicitly include micro coaxial cable assemblies, medical cable assemblies, UAV/drone assemblies, RF coaxial assemblies and fine/ultra-fine electronic wire.

8. Ask for DFM Review Before Prototype Production

Before placing a prototype order, OEM engineers should ask:

Can the design be manufactured consistently?

A useful DFM review can examine:

• cable diameter versus connector size
• stripping dimensions
• conductor exposure
• termination access
• shielding termination
• strain relief
• bend radius
• assembly sequence
• inspection access
• tooling requirements

If → the drawing contains a dimension that is difficult to assemble repeatedly

Then → discuss the tolerance and manufacturing method before prototype release

Why → an unnecessarily tight or inaccessible feature can create production variation.

If → the prototype requires extensive manual adjustment

Then → discuss how the same feature will be controlled in production

Why → prototype assembly methods do not always scale directly to volume manufacturing.

The current HOTTEN article already emphasizes reviewing manufacturability before quotation and considering tooling, process controls and automated inspection as volume increases.

9. Separate Prototype Requirements From Mass-Production Requirements

A project should ideally specify:

Prototype

→ Engineering Validation

→ Pilot Production

→ Mass Production

The requirements may change at each stage.

If → the project is currently at prototype stage

Then → define prototype quantity and validation objectives

Why → the supplier needs to understand what the prototype is expected to prove.

If → the project is intended for long-term production

Then → communicate expected annual volume and production timing early

Why → tooling, process controls, inspection and production planning can depend on expected volume.

The current article specifically distinguishes prototype quantities from production volume and notes that higher-volume projects may require dedicated tooling and more standardized assembly processes.

10. Define Testing Before the Supplier Builds the Prototype

Testing should not be added only after the prototype arrives.

Depending on the application, the RFQ may specify:

If → a parameter is critical to system performance

Then → define its acceptance criterion before prototype testing

Why → both OEM and supplier need the same definition of pass/fail.

If → the test method is important to qualification

Then → specify the measurement method or required report format where possible

Why → results from different measurement methods may not be directly comparable.

This connects directly to the fourth article on impedance and the third article on flex-life qualification.

11. Define Documentation and Traceability Requirements

For OEM projects, the deliverable may include more than the physical cable.

Depending on the project, the customer may request:

• inspection report
• electrical test report
• material information
• connector information
• dimensional report
• process records
• sample approval records
• change notification
• lot identification
• packaging requirements

If → the cable is part of a controlled OEM production program

Then → define documentation and traceability requirements before production begins

Why → documentation requirements may affect the supplier's production and quality-control process.

The current HOTTEN page already identifies inspection, documentation and packaging as production-stage requirements.

12. Use an Engineering Review When Some Specifications Are Unknown

Not every OEM arrives with a complete specification.

That is especially common during:

• new product development
• prototype development
• connector redesign
• miniaturization
• replacement of an existing supplier
• adaptation of an existing cable

If → the OEM knows the application and interface but not the exact cable construction

Then → share the known system requirements and request an engineering review

Why → the supplier may help determine suitable cable construction, dimensions and validation requirements.

If → the OEM has an existing sample but incomplete documentation

Then → provide the sample and identify which characteristics must remain unchanged

Why → the supplier can distinguish fixed requirements from areas that may be redesigned.

The current HOTTEN article already states that application/interface information can be useful even when the OEM does not yet know every cable specification.

What Should an OEM Send With a Cable Assembly RFQ?

A useful RFQ package can be organized into:

Engineering Information

• application description
• system interface
• electrical requirements
• mechanical requirements
• environmental requirements
• drawings
• CAD files if available
• connector part numbers
• pinout
• cable length
• quantity

Validation Information

• required electrical tests
• mechanical tests
• flex requirements
• environmental tests
• acceptance criteria
• report requirements

Production Information

• prototype quantity
• target annual volume
• production timing
• MOQ expectations where applicable
• packaging
• documentation
• traceability requirements

Commercial / Project Information

• prototype versus production phase
• target launch timing
• forecast information
• required sample date
• change-control expectations

This makes the RFQ much more useful than sending only:

“Please quote this cable assembly.”

Practical OEM Cable Assembly Specification Logic

A complete specification process can be simplified as:

Application

→ Signal / Power Requirement

→ Interface

→ Cable Construction

→ Connector

→ Mechanical Envelope

→ Environmental Conditions

→ Testing

→ Prototype

→ Engineering Validation

→ Pilot Production

→ Mass Production

For a medical micro coaxial cable assembly:

Medical Imaging Device

→ define signal channels

→ define frequency / bandwidth

→ define impedance and capacitance requirements

→ determine cable OD and routing space

→ define flex requirements

→ specify connector and pinout

→ define cleaning / sterilization conditions where applicable

→ establish electrical and mechanical tests

→ prototype

→ validate

→ pilot production

→ mass production.

For an RF cable assembly:

High-Frequency RF System

→ define operating frequency

→ establish nominal impedance

→ define insertion-loss and return-loss requirements

→ determine cable length

→ select cable construction

→ define connector

→ validate termination and transition

→ perform VNA / relevant RF testing

→ validate production repeatability.

For a UAV or robotics cable assembly:

Moving Platform

→ define movement profile

→ determine bend radius

→ define vibration / torsion requirements

→ establish cable OD and weight constraints

→ select cable structure

→ define connector and strain relief

→ perform flex / vibration validation

→ validate pilot production.

Related HOTTEN Engineering Resources

How Micro Coaxial Cable Design Ensures Signal Integrity in Medical Devices

Design Factors in Medical Cable Assemblies That Protect Signal Integrity in Clinical Devices

How Flex-Life Testing Helps Medical Cable Assemblies Maintain Performance After Repeated Bending

What Is Cable Impedance and Why Does It Matter in High Frequency Cable Assemblies?

How RF Coaxial Cable Assemblies Control Impedance and Loss for Reliable High-Frequency Signals

How Custom Medical Cables Are Processed and Inspected Before Delivery

Medical Cable Assembly

Micro Coaxial Cable Assembly

RF Coaxial Cable Assembly

Frequently Asked Questions

What is a custom cable assembly?

A custom cable assembly is a cable manufactured or configured to meet the electrical, mechanical, connector, dimensional, and environmental requirements of a specific application.

What information is needed to quote a custom cable assembly?

Typical information includes cable type, cable length, connector configuration, electrical requirements, mechanical requirements, environmental conditions, quantity, and testing requirements. If some specifications are not available, the application and interface information can still provide a useful starting point.

How long does a custom cable assembly take to develop?

Development time depends on cable construction, connector availability, tooling requirements, testing, and project complexity. Prototype development and production qualification should be considered separately.

Can a custom cable assembly use customer-specified connectors?

Yes. A project can be developed around specified connectors when the connector part number and interface requirements are available. Connector compatibility should be reviewed together with cable dimensions and assembly requirements.

What is the difference between a cable assembly and a wire harness?

A cable assembly generally refers to a finished cable with one or more connectors or terminations. A wire harness can contain multiple wires, cables, branches, terminals, and protective components. The terminology varies between industries and manufacturers.

Should I specify the cable first or the connector first?

Neither should always be selected independently. Cable construction, connector interface, available space, electrical performance, and assembly requirements should be evaluated together.

Conclusion

A good custom cable assembly specification does more than list a cable type and connector. It describes how the assembly will function inside the finished product.

For OEM projects, the most important information usually includes:

1. Application and signal requirements

2. Electrical performance

3. Mechanical movement and installation

4. Connector configuration

5. Environmental conditions

6. Testing and production requirements

When these requirements are defined early, the cable assembly manufacturer can make better decisions about materials, construction, connectors, assembly methods, and validation.

For OEMs developing compact medical equipment, UAVs, robotics, RF systems, or other high-performance electronics, early engineering collaboration can help turn a basic cable requirement into a manufacturable and production-ready cable assembly.