How to Specify Cables for Transport Equipment

Start with the environment, not the part number

Before choosing a cable or connector, write down what the part will actually experience. Every item below should end up as a drawing note or a referenced specification.

Exposure	Questions to answer	What it drives
Temperature	Lowest and highest ambient? Heat from exhaust, brakes or motors? Flexed when cold?	Insulation and jacket rating, and cold-bend performance
Fluids	Diesel, hydraulic oil, coolant, de-icing fluid, cleaning chemicals, salt spray?	Jacket compound and connector seal material
Water	Rain and spray, submersion, or high-pressure washdown?	Sealing and IP rating
Sunlight and ozone	Permanently outdoors?	UV- and ozone-resistant jacket
Mechanical	Abrasion, crush, impact, being driven over?	Jacket thickness, armour or conduit, routing
Movement	Static, occasional flex, continuous flex or coiled?	Conductor stranding, cable construction, strain relief
Vibration	Road, rail, engine or airframe?	Clamping intervals, connector locking, crimp quality
Mating cycles	Plugged once, or daily?	Connector durability rating and contact plating

Jacket materials at a glance

Material	Strengths	Watch for
PVC	Low cost, widely available	Stiffens and cracks in cold; limited oil resistance unless specified
Polyurethane (PUR)	Very good abrasion and oil resistance, good for continuous flex	Grade matters for hydrolysis and heat
Thermoplastic elastomer (TPE)	Flexible across a wide temperature range, good for overmoulding	Fluid resistance varies by grade
Rubber (e.g. CR, EPDM compounds)	Rugged, flexible, good weathering; common for heavy-duty power leads	Heavier; oil resistance depends on compound
Cross-linked polyolefin	Heat and abrasion resistant; common in primary wire	Less flexible as a jacket
Fluoropolymers (e.g. ETFE)	High temperature and chemical resistance, thin walls; aerospace	Cost; follow the governing aerospace specification

Sealing: say which rating, under which standard

"Waterproof" is not a specification. Ingress protection is defined in IEC 60529 (for example IP67, temporary immersion). For road vehicles, ISO 20653 adds ratings such as IP6K9K for high-pressure, high-temperature washdown. State the rating, the standard, and whether it applies mated, unmated or both. An unmated connector is often not sealed at all.

Strain relief and flex life

For any cable that moves, the most important location is where it leaves the connector. Specify the strain relief method (moulded boot, gland or backshell clamp) and, where it matters, a pull-force requirement. For continuously moving cables, specify fine-stranded conductors and a cable designed for flexing, and state the bend radius and expected number of cycles.

Drawing notes that prevent arguments

Workmanship standard and class, for example IPC/WHMA-A-620 Class 2 or Class 3.
Cable and connector part numbers, with approved alternates or "no substitution".
Sealing rating and standard, and mated or unmated condition.
Electrical tests: continuity on every part, plus insulation resistance and hipot values where needed.
Marking: part number, revision and date or serial, with method and location.
Packaging that protects the moulded ends and prevents kinking.

For the full list of what to send a manufacturer, see the cable assembly RFQ checklist.