Wire Harness Protection by Position
A harness is not one protection problem: it is six. The trunk that must not chafe, the connector that must not get wet, the branch that flexes every cycle, the zone that gets hot, the bundle that must stay organized. This page treats each position on its own terms, then closes with the decision matrix and the RFQ checklist that turn a drawing into sized part numbers.
Position 1 — Basic electrical insulation
The baseline: a recovered polyolefin wall over bare or lightly insulated runs inside cabinets and machines. The inputs are the grip OD and the temperature at the hottest point on the run: published polyolefin bands stop at +125 °C, so anything hotter moves the position to the silicone or fiberglass sections. Halogen-free grades apply where enclosed spaces or transit work demand low smoke toxicity. Where the run is straight and the fit is simple, a 2:1 tube is the correct answer, stepping up the ratio only costs wall and money.
Position 2 — Connector transitions and sealing
Connectors create the two classic tubing problems: a bulge the tube must clear, and a joint that must not wick water. A 3:1 or 4:1 dual-wall adhesive tube answers both at once, the higher ratio clears the lug or overmould, the melting adhesive closes the ends against capillary moisture. The deciding input is whether the position ever gets wet: indoor dry panels do not need the adhesive at all. Where the transition angle is steep or the branches split, a moulded breakout boot beats any straight tube.
Position 3 — Abrasion zones
Where the harness passes an edge, a clamp or a moving part, the jacket wears before the insulation fails. PET braided mesh and textile wraps are the purpose-built answers: they flex with the harness, expand over connectors, and can be opened for rework. Heat shrink also works as a sacrificial cover but is permanent. The honest inputs are motion type (continuous flex vs static rub) and access: if the harness will be serviced, choose the removable form.
Position 4 — Fluid and chemical exposure
Fluids select the family before temperature does. Silicone handles ozone, UV and many automotive fluids by published note; fluoropolymer (PTFE/FEP/PFA) is the purpose-built answer for fuel, solvent and chemical duty to +260 °C; PVC and standard polyolefin have no published chemical tables on this site, so treat them as unverified for immersion duty and name the fluid when you enquire. Do not let a generic "oil-resistant" claim stand in for the fluid name.
Position 5 — Temperature zones
Rank every point on the harness, not its average: engine-adjacent branches, exhaust crossings, and lead exits each get their own family. Practical bands from published data: polyolefin to +125 °C, silicone and silicone-coated fiberglass to +200 °C, fluoropolymer to +260 °C, fiberglass composites and polyimide above that. One hot spot above a family's band disqualifies the family for that branch: zone the harness and mix families rather than over-specifying the whole bundle.
Position 6 — Bundling and organization
Bundling is mechanical: self-winding and velcro textile wraps and PET mesh organize a trunk without disconnecting it, and the zipper heat-shrink tube adds a reopenable heat-shrink option where the identification must survive. Colour and marking inputs belong here. After a tube recovers, the label under it is invisible, so print before you insulate.
Decision matrix
| Problem | Candidate family | Buyer inputs that decide it |
|---|---|---|
| Insulate a straight run, dry | Single-wall polyolefin 2:1 | Grip OD, temperature, colour |
| Seal a connector, wet or outdoor | Dual-wall adhesive 3:1/4:1 | Bulge OD, grip OD, recovery heat on site |
| Branch splits under motion | Moulded breakout boot | Finger count, core ODs, jacket OD |
| Jacket chafes on an edge | PET braid or textile wrap | Bundle OD, motion type, service access |
| Fuel, solvent or chemical splash | PTFE / FEP / PFA tubing | Fluid name, temperature, wall |
| Engine or exhaust heat zone | Silicone tubing or silicone-coated fiberglass | Peak temperature, flex duty |
| Trunk needs organizing on a built loom | Self-winding / velcro textile | Diameter range, reopenable or not |
| Enclosed-space routing, low toxicity | Halogen-free DRS range | Grade declarations required, OD |
RFQ checklist
Send these eight inputs with a harness enquiry and the answer comes back as sized part numbers, not options:
- Largest OD the sleeve must slide over (connector, overmould, splice block)
- Smallest OD it must grip with 15–25% compression
- Jacket / substrate material under the sleeve
- Temperature : worst continuous and peak, per zone
- Fluid exposure : named fluids, or "none"
- Cut lengths and tolerance, if pre-cut
- Annual quantity and release pattern
- Marking / colour if identification matters
Send the harness drawing, get sized part numbers
Largest and smallest OD, temperature and fluid per zone, cut lengths and quantity: we return one family per position with cut sizes.
Frequently asked questions
Should I use adhesive-lined or single-wall tubing on a harness?
Use adhesive-lined (dual-wall) where moisture can reach the connection: outdoor routing, wash-down areas, or any connector that sits below the drip line. Use single-wall everywhere else - it insulates and identifies at lower cost and recovers with less heat. The seal is not incremental; adhesive that never fully flows leaves a channel, so if you specify dual-wall, specify the recovery heat that melts it.
When does a harness need textile or braid instead of heat shrink?
When the harness must stay serviceable or flexes for its whole life. PET braid and textile wraps slip on over connectors and come off for rework; heat shrink is permanent - the removal path is a knife. Choose braid for abrasion zones with maintenance access, heat shrink for sealed, forget-it positions. Many finished harnesses use both: braid over the trunk, adhesive-lined tube at the connector breaks.
What harness data gets a sized recommendation instead of a catalogue answer?
The largest OD the sleeve must slide over, the smallest OD it must grip, the jacket material, the worst continuous temperature and fluid at any point on the run, the flexing duty, cut lengths, and annual quantity. Add marking or colour needs if identification matters. With those inputs we name one family per position and return cut sizes - no catalogue guessing.