Most articles classify wire harnesses by industry; this one classifies them the way an engineer actually chooses: by the requirements that force each construction decision. Work through the four decision layers below and the harness type at the end is not an opinion — it is the consequence of your constraints.
Layer 1: Environment — What Will Attack the Harness?
Environment eliminates options faster than any other factor. Dry indoor cabinet → standard PVC builds are fine. Heat (engine bays, ovens, drives) → cross-linked or silicone insulation with temperature-matched sleeves. Water and washdown → sealed connector systems with wire seals and overmolded transitions, targeting an explicit IP rating per zone. Oil and chips (machine tools, engines) → PUR jackets and armor. UV and weather (solar, outdoor signage) → UV-stable jackets and sealed connectors, because ordinary PVC embrittles in a season. Flex (robots, doors, chains) → chain- or robot-rated cable with fine stranding — the single most violated rule in industrial purchasing, covered in our flexible flat cable and robot cable guides.
Layer 2: Current and Voltage — What Must It Carry?
Current defines conductor cross-section, and cross-section defines everything mechanical. Low-level signals live in 26-30 AWG where connector contact quality matters more than copper. Power circuits follow the two-calculation rule: thermal ampacity and voltage drop, with derating for bundling and ambient temperature. High-voltage new-energy circuits add shielding, interlock loops and safety-jacket color rules. Our wire gauge guide covers the calculations.
Layer 3: Signal Type — What Is the Sensitive Part?
Every harness mixes 'whatever' circuits with a few that actually need care: encoder and analog feedback lines that need individual shields, differential data pairs that need controlled geometry, RF runs that need true coax. Identify the sensitive circuits first; their requirements shape the bundle more than the power circuits do. A practical rule: if a circuit's failure mode is 'intermittent and impossible to reproduce', its harness construction deserves an upgrade before the electronics do.
Layer 4: Construction — Open, Jacketed, Flat or Overmolded?
The final layer picks the physical form: open loom (cheapest, serviceable, standard for appliance and vehicle interiors), jacketed round assembly (clean routing, one mechanical entity, standard for machinery), flat/FFC constructions (space-constrained, controlled spacing — see our FFC guide), and overmolded builds (best sealing and strain relief, needs tooling — justified by volume or harsh duty).
Putting It Together: Two Examples
- Solar tracker signal harness: outdoor UV + flex + low-level signals → UV-stable PUR jacket, fine-strand shielded pairs, sealed connectors, IP65+ target, jacketed round form.
- Washing machine main loom: humidity + heat near heater + cost pressure → flame-rated PVC insulation, sealed connectors only below the water line, heat-resistant sections near the heater, open-loom form with tape bundling.
Kaweei manufactures across all four construction families for industrial, automotive, medical and energy customers. If you have requirements but not a drawing, contact our engineering team — we turn the four layers above into a buildable specification.