Tape Wrap, Split Conduit and Braided Sleeve: Choosing Protection for a Vehicle Harness

A vehicle harness rarely fails in the middle of a conductor. It fails where the bundle rubs a bracket edge, where it crosses a bulkhead without a grommet, where radiant heat off an exhaust run cooks the insulation, or where water tracks along the outside of the bundle and pools inside a connector. That is why automotive wiring harness tape wrap, conduit and sleeve protection belongs on the drawing as a specified item rather than as a finishing touch — and it is the line most buyers send to a Chinese harness shop blank, along with a quiet assumption that "wrapped" means the same thing to both parties.

It does not. "Wrapped" covers everything from a 15-cent bundling tape that abrades through in a hundred strokes to a fabric tape that survives thousands. Below is what each covering actually does, the two class numbers that make the spec enforceable, and how to write it so a quote from three different shops is comparing the same thing.

Three coverings, three different jobs

Tape

Tape does three jobs at once, which is why it dominates vehicle harness work: it bundles the branches, it puts a sacrificial layer between the bundle and the sheet metal, and — in the right material — it stops the harness buzzing against a panel at idle.

The word "tape" on a drawing is close to meaningless, because the families behave nothing alike:

• PVC tape. Cheap, flexible, conformable, common on aftermarket and in-cabin work. It is also the family that softens, unwinds and turns gummy at sustained engine-bay temperatures, and whose plasticiser can migrate into some wire insulations over years of heat. Typical continuous ratings sit in the 85–105 °C band; treat anything higher as a claim to verify.
• Acetate cloth tape. Quiet, tears cleanly by hand, conforms well around branches. Moderate temperature (commonly around 105 °C), poor moisture resistance. Popular in cabin bundles where noise matters more than fluid exposure.
• PET fleece (nonwoven polyester) tape. The noise-damping grade. Thick, soft, absorbs rattle; used on bundles that run against trim or through a dash. Abrasion performance is moderate, not high.
• Woven PET fabric tape. The abrasion grade. This is what goes where the bundle touches a bracket or passes an edge, and where continuous temperatures push toward 125–150 °C depending on the adhesive system.

Two things follow. First, a harness is normally taped in more than one tape — a bundling tape over most of the run, a fabric tape at the two or three contact points. Second, a shop quoting "tape wrap included" without naming families is quoting the cheapest one.

Split conduit

Convoluted (corrugated) tubing, slit lengthwise so the bundle drops in. It is the only one of the three that gives real crush and impact protection, and the only one that a technician can open in the field with bare hands.

Material sets the envelope: polypropylene is the low-cost grade, roughly −40 °C to around +100 °C; PA6 and PA12 push toward +150 °C with better fluid and low-temperature impact behaviour, PA12 being the one usually specified where hydrolysis and cold impact both matter. Confirm the range against the tubing maker's data rather than the harness shop's memory.

The slit is both the feature and the weak point. A conduit that is free to rotate will eventually present its slit to the abrasion source, at which point it is protecting nothing. Conduit has to be retained — clipped, or locked at each end.

Braided sleeve

Expandable PET monofilament braid. It slides on, it expands over connectors and branches, it breathes so no water sits inside it, it takes heat well (commonly quoted around −50 °C to +150 °C continuous, with the monofilament melting far higher), and you can still see the wires through it, which inspectors like.

What it does not do: seal, resist crush, or stay put at a cut end. Standard braid frays the moment it is cut cold. Self-closing (wrap-around) braid, which has a memory-set overlap, opens for service; plain sleeving does not — it has to be slid off an end, which means disconnecting something.

Side by side, that is the comparison that belongs in your sourcing file:

Values are typical industry ranges for the material families, not a specification for any one supplier's stock. Ask for the datasheet of the exact product being used.

Writing a covering spec that is enforceable

The two class numbers

The reason most harness protection specs are unenforceable is that they describe a material instead of a performance class. The vehicle industry solved this years ago with LV 312, the joint test specification used for harness tapes. It grades tape on abrasion resistance in letter classes (A through E, where A is essentially a bundling tape with no meaningful abrasion protection and E is the heavy fabric grade you put on a contact point), on temperature in T-numbers, and separately on noise damping. The abrasion test drags the taped bundle across a defined mandrel and counts strokes to breakthrough; the published bands run from under a hundred strokes at the low end to several thousand at class E on a small-diameter mandrel. Treat those stroke figures as indicative and put the class letter in the contract, not the stroke count — the bands have been revised across editions, and the letter is what a tape maker's datasheet will state.

Write it like this and a factory in Shenzhen and a factory in Poland will quote the same harness:

Main bundle: tape, LV 312 abrasion class B minimum, temperature class per T-rating ≥ 105 °C, applied at 50% overlap. Zones C1–C3 (bracket contact, see drawing): tape, abrasion class D minimum, ≥ 125 °C. Branch from X to Y: PA6 split conduit, ID 13 mm, retained by clip at both ends, tape-locked 25 mm onto conduit.

That is three lines. It removes almost every substitution argument you would otherwise have at first article.

The spec line most buyers leave blank: overlap

Ask ten buyers what tape overlap their harness is built at and nine will not know. It is the number in the covering spec that moves the most, because it sets both coverage and cost:

• 50% overlap ("half-lap") gives two layers of tape everywhere. Full coverage, highest material use, highest labour time.
• 33% overlap is the common production compromise — continuous coverage, one and a half layers.
• Open spiral (candy-stripe, gaps between turns) is a bundling wrap only. It holds the loom together and costs almost nothing. It is not protection, and it is what you get by default when the drawing says "tape" and nothing else.
• Spot taping — a few turns every 100–200 mm — is for holding branches during assembly. Same caveat.

State the overlap, state where each style starts and stops with a tolerance (±10 mm off a connector face is a normal call-out), and state how branches are treated. A harness built at open spiral and a harness built at 50% overlap can differ by a meaningful fraction of the assembly minutes in the quote, which is exactly why the two shops you are comparing may not have quoted the same thing. If you are still building the drawing package that carries these call-outs, the sequence in how to write a product spec sheet for a Chinese factory is a reasonable skeleton to hang them on.

Zone by zone

Details that separate a harness shop from a wire cutter

Four things experienced harness engineers specify and inexperienced buyers discover the hard way.

Tape-lock the conduit ends. Where tape meets conduit, the standard practice is to run the tape 20–30 mm onto the conduit at each end. It stops the conduit migrating along the bundle and stops the slit rotating. A conduit that is not locked will, over a few thousand kilometres of vibration, walk clear of the exact spot it was there to protect.

Hot-cut the braid. PET braided sleeve cut with side cutters unravels. Cut ends should be hot-knife cut, or sealed with adhesive-lined heat-shrink. If your inspection photos show a frayed sleeve end at a connector, the shop cut it cold.

Covering changes clip sizing. Tape adds 0.3–1 mm per layer to bundle diameter; conduit adds several millimetres. If the vehicle-side clips and grommets were sized against a bare bundle diameter, a fully wrapped harness will not seat, and the assembly line's fix — forcing it — is the failure you will see in warranty. Dimension the drawing at finished diameter over the covering, and give a tolerance.

Wrap direction versus water. On a run that slopes, tape wound so its overlap faces uphill turns the harness into a wick that carries water down the adhesive line into a connector. Wound the other way it sheds. On any harness that runs from a wet zone to a dry one, the drawing should also call a drip loop before the connector.

None of this substitutes for the joints being sound underneath — covering hides a bad crimp as effectively as it protects a good one, which is why crimp acceptance is judged on its own terms and crimp height, pull-force and cross-section get their own inspection line.

A protection spec a factory can quote without guessing

1. Finished (over-covering) bundle diameter at every clip and grommet position, with tolerance.
2. Tape family and abrasion class per zone, plus temperature class.
3. Overlap percentage per zone, with start/stop positions and tolerance.
4. Conduit material, inside diameter, and slit orientation relative to the abrasion source.
5. Conduit retention method and clip positions.
6. Tape-lock length at every tape-to-conduit and tape-to-connector transition.
7. Braided sleeve type (standard versus self-closing) and end treatment.
8. Branch and breakout treatment — where covering stops relative to the branch point.
9. Which zones must be openable for field service.
10. Sample approval criterion: first article measured over the covering, photographed at each transition.

Common questions

Is conduit the better choice by default?

No. Conduit is better at crush, impact and serviceability; it is worse at noise, it adds diameter you may not have room for, and it does nothing where the bundle is tightly routed against a curved bracket. Most production vehicle harnesses use both, zoned.

Can a supplier substitute a different tape mid-order?

If your drawing says "tape", yes, and it will not be a contract breach. If it says an abrasion class and a temperature class, a substitution is documentable. This is the practical reason to specify by class.

How do I check the covering on an inspection report?

Ask for photographs at every transition — connector-to-tape, tape-to-conduit, branch points, and both cut ends of any sleeve — plus a caliper measurement of finished diameter at the clip positions. Those photos catch open-spiral wrap, cold-cut braid and unlocked conduit in about thirty seconds. The general framework in product inspection before shipment applies here; the harness-specific part is the transition photos.

What to ask the supplier next

Before you approve a first article on a wrapped vehicle harness, send these questions and expect written answers:

• Which tape families do you stock, and can you send the maker's datasheet for each, showing abrasion class and temperature class?
• Is taping done by hand, semi-automatically, or on a taping machine — and does that change between sample and production run?
• What overlap do you build at by default when the drawing does not state one?
• Do you buy conduit and sleeve per order or stock it, and what material grade?
• Can you photograph a finished harness at every covering transition as part of outgoing QC?
• Will the sample be built with the same coverings, from the same rolls, as the production run?

As a worked example: Huisheng Electronics in Longhua District, Shenzhen — incorporated 2016 and checked against the Chinese corporate registry in August 2026 — lists wrapped vehicle harness assemblies, adapter and ignition leads and multi-circuit vehicle harnesses among its six product lines, with a supplier-published roster of more than twenty production and test machines including automatic cut-strip-crimp units, servo crimping presses and forming machines. What the published information does not settle is exactly the list above: which tape families are stocked, what temperature and abrasion classes those tapes carry, and whether taping is machine-assisted. Those are questions to put in writing before you commit, alongside stated trade terms — MOQ 1,000 pieces, samples dispatched in 7–10 days, volume in 15–25 days — which are the supplier's own figures and worth confirming at quote time. For background on how this cluster of suppliers is structured, the Shenzhen electronics manufacturing sourcing guide covers the ground, and buyers running vehicle programs will recognise the same documentation discipline described in the automotive electronics manufacturing guide.