Designing a custom cable entails an in-depth specification process, and the more clearly you define your needs, the more accurate your quote will be, and the more reliably your cable will perform in your specific application.
In this guide, we will walk you through every decision you need to make so you can confidently prepare a full custom cable specification before you approach a manufacturer.
Why Custom Cable Specifications Matter
A custom cable is not a standard off-the-shelf product; it’s an engineering component designed to perform under specific conditions. When a specification is incomplete or unclear, manufacturers are forced to make assumptions, which can lead to over-engineered cables, under-performing cables, or compliance issues.
The Complete Custom Cable Specification Checklist
What Is the Cable Used For?
The first step is defining the application clearly. You should ask yourself:
- What equipment is the cable connecting?
- Is it carrying power, signal, data, or a combination?
- Will it be installed internally within a device or externally in the field?
- Is the cable fixed in place or in motion during operation?
- Is this a prototype, a one-off replacement, or a production run?
This context will shape every design decision going forward.
Operating Environment
Next, you must outline the operating environment. This is one of the most important factors in custom cable design, as many cables fail due to underestimated environmental conditions. You should therefore clearly define:
- Temperature range – both minimum and maximum temperatures
- Chemical exposure – any exposure to oils, fuels, cleaning solvents, acids, etc.
- Mechanical stress – detail whether the cable will be exposed to any vibration, abrasion, crushing, or repeated flexing.
- Outdoor or harsh conditions – consider if the cable will be exposed to UV, rain or moisture, or dust.
Electrical Requirements
Electrical performance is the core of any specification, so you should clearly state:
- Voltage rating – define operating voltage as well as peak or surge voltage.
- Current-carrying requirements – higher currents need larger conductor cross sections.
- Signal type – clarify what type of signal the cable carries (e.g. low-voltage, analogue, digital, etc.)
- EMI sensitivity – clarify if your cable will operate in a noisy environment, as it may need certain shielding.
Number of Conductors
The number of conductors defines the internal structure of the cable. It defines the internal architecture of the cable, and everything else is influenced by how many electric paths the cable must carry. You may need single-core cables, multi-core cables, twisted pairs, or mixed constructions.
Conductor Material and Size
The choice of conductor material determines how a cable will perform electrically, mechanically, and environmentally. Most cables use copper-based conductors, but different types are selected based on requirements.
- Bare copper – excellent electrical conductivity and cost efficiency.
- Tinned copper – useful in humid, outdoor, or industrial environments.
- Silver-plated copper – used in aerospace, defence, and advanced communication systems.
The size of a conductor is usually specified in mm², and it directly affects the cable’s electrical and physical characteristics.
Insulation Material
The insulation on a custom cable defines its thermal and chemical performance. Common materials that you can specify include:
- PVC – cost-effective, general use
- XLPE – improved thermal resistance
- Silicone – excellent flexibility and temperature range
- PTFE – high temperature and chemical resistance
- FEP / ETFE – thin-wall, high-performance applications
Shielding Requirements
Shielding is the layer of the cable that protects against electrical interference and signal degradation. The options you have include:
- No shielding – for simple power cables
- Foil shielding – high coverage and lightweight
- Braided shielding – durability and flexibility
- Combination – maximum protection
Outer Jacket
As the outermost layer of the cable, the jacket protects the entire cable from external damage. The type of jacket needed depends on the environment and application. You should therefore consider:
- Flexibility requirements
- UV resistance
- Oil and chemical resistance
- Abrasion resistance
- Flame retardancy
Common materials include PVC and polyurethane. You can specify the exact material needed or request advice from a cable expert.
Flexibility Requirements
Not all cables are static – many are needed for dynamic applications which have different requirements. You should therefore specify whether the cable is:
- Fixed installation
- Occasionally flexed
- Continuously flexed
- Used in drag chains or robotics
Dynamic applications usually require fine-stranded conductors, flexible insulation systems, and controlled bend radius design. By ignoring or miscalculating how much movement is required, you are at risk of premature cable failure.
Cable Length
Cable length is often underestimated in cable design, but when measured inaccurately, it can cause issues like failure, clutter, signal issues, and extra costs. Define the strength by thinking beyond the point-to-point measurement, and consider how it will be installed and used. Also consider:
- Service loop or slack
- Routing considerations
- Tolerance allowances
Compliance & Standards
By defining compliance requirements early in the process, you can ensure materials, methods, and testing procedures are aligned in order to prevent redesigns and requalification.
Common standards include:
- RoHS (Restriction of Hazardous Substances)
- REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals)
- UL certification (Underwriters Laboratories)
- ISO 9001 quality management systems
- AS9100 aerospace standard
Different industries may need additional standards depending on the application.
Need Help Specifying a Custom Cable?
If you’re unsure about any part of your cable specification, you don’t need to have everything perfectly defined before getting in touch.
The engineering team at K. Lacey Cables can review your requirements, help refine your design, and recommend the most suitable materials, construction, and connector options for your application. Contact us today for more information.