1
It should have been a cable
Discrete wires bundled by hand where one multiconductor cable would do. More parts, more build steps, more failure points.
This guide explains how to bundle a wire harness by first deciding whether the design should be a multiconductor cable, then choosing the correct covering, branch structure, securing method, and manufacturer handoff.
How to bundle a wire harness like a pro
Most harness mistakes are design choices, not crimp-tool mistakes. We see the same four repeatedly: wrong cable-or-bundle call, wrong covering, messy branches, and weak handoff detail.
Decide whether each run should be a standard multiconductor cable or a bundle of discrete wires. Then choose braid, loom, or tape for each segment, and use heat shrink only for ends, boots, strain relief, and sealing.
Short Version
How to bundle a wire harness: short version
If you only need the buildable path, use this sequence. The covering comes after the electrical architecture, not before it.
- 1
Decide cable or bundle
Start with cable when motion, shielding, sealing, or a standard conductor mix makes the run simpler. Bundle discrete wires when the run branches heavily, conductor count gets high, or no standard cable fits.
- 2
Lay out the wire list
Name every net, connector cavity, wire gauge, color, and insulation family before thinking about braid, loom, or tape.
- 3
Group by destination
Route wires into trunks and branches by where they land. Keep branches as Y and T junctions; redesign anything that wants an octopus.
- 4
Secure without crushing
Spot-tie every 6 to 12 inches. The tie should stop sliding without flattening insulation or forcing a tight bend.
- 5
Pick the covering per segment
Use PET braid by default, split loom for abrasion, harness tape for low-profile in-box runs, and heat shrink only for ends, boots, strain relief, and sealing.
- 6
Finish and test
Terminate the ends, add labels and strain relief, then inspect routing and verify continuity before the harness goes into the machine.
Common Failure Modes
The four mistakes we see most
None of these are manufacturing problems at first. They are design choices that make manufacturing harder than it needs to be.
2
Octopus junctions
Six or eight legs fanning out from a single point. Clean on a screen, impossible to cover well, fragile in service.
3
All-black wires
No color coding. Slow to route, slow to build, hard to troubleshoot later.
4
Over-defined splice locations
Drawings that pin the exact position of every splice instead of naming which wires connect and leaving placement to the builder.
Cable-First Decision Flow
Decide the architecture before the covering
The first branch is not braid versus wire loom. It is cable versus bundle. Covering selection only starts after that answer is clear.
First Decision
Motion, sealing, shielding, or a standard cable fit?
If yes, start with a multiconductor cable. It usually removes parts, build steps, and failure points.
If No
Pick the covering by environment
PET braid is the default. Use split loom for abrasion, harness tape for low-profile in-box runs, or no jacket where spot-tying is enough.
Any Bundle
Secure, branch, then finish the ends
Secure every 6 to 12 inches, use simple Y/T breakouts, and keep heat shrink to ends, boots, strain relief, and sealing.
Start with cable when it removes risk
Continuous flex, shielding, sealing, and standard conductor mixes should start as cable searches, not covering debates.
Bundle when the run branches
Many branches, high conductor counts, heat/current grouping, or no standard cable fit push the design back to discrete wires.
Covering is a separate decision
PET braid, split loom tubing, and wire harness tape solve different problems. Choose after the cable-or-bundle question.
Heat shrink is not a jacket
Heat shrink tubing belongs at ends, boots, strain relief, and seals. Covering choice alone does not establish an IP rating.
Architecture
Cable or bundle?
Before bundling, ask whether it should be a cable. The default move is to grab discrete wires; the better one is usually a multiconductor cable. Fewer build steps, fewer failure points, a cleaner result.
Start with a cable when:
- High-flex or robotics. Continuous-flex and drag-chain motion fatigue hand-bundled wires. Use flex-rated cable like igus chainflex.
- Sealed or washdown (IP67). Start with jacketed cable, but the IP rating comes from the connector, gland, boot, overmold, and validation strategy at every transition.
- EMC or shielding-critical signals. A shielded cable beats hand-wrapped shielding.
Where we shop
igus chainflex for continuous-flex and robotics, Alpha Wire for a solid standard, Belden and Tensility for budget.
Cable has a ceiling
Above roughly 10 to 20 conductors it gets expensive and hard to source. Branch-heavy runs often hit that wall sooner. Past that, bundle discrete wires.
Covering
Picking a covering
Two separate decisions people run together: the covering (the jacket over the run) and securing/branching (what holds it together). Keep them apart.
PET braided sleeve (default)
Flexible, breathable, abrasion-resistant, cheap, fast. Expandable braided sleeving slides over connectors and contracts to grip; split braid takes added wires later without unplugging. Cap the ends with heat shrink so they don't fray.
Common miss: untreated ends, wrong fill, or forcing it over an octopus junction.
Convoluted (split-loom) tubing
More mechanical and abrasion protection. Right for under-hood, outdoor, and abrasive runs. Split versions snap on for service. Holds a rigid junction when that helps. Terminate with heat shrink or tape.
Common miss: running wire loom inside an enclosure, where the stiffness and bulk get in the way. Or oversizing it.
Harness tape
Low-profile, conforms tight, doesn't snag. tesa 51608 PET fleece is common for flexible, noise-damping interior wraps; tesa 51036 PET cloth is for higher-abrasion, higher-temperature automotive protection. Apply half-lapped.
Common miss: vinyl electrical tape (3M Super 33) as the primary wrap. It gums, unwinds, leaves residue. Use wire harness tape.
Heat shrink is not a jacket
Heat shrink tubing is for short sections: end caps, breakout boots, connector strain relief, sealing. It comes adhesive-lined (sealing, strain relief) and plain (general). Don't run it the length of a bundle.
Shrunk, it's rigid, so it kills flex and cracks, can't be opened to service a wire, traps heat, and costs far more per foot than braid. Full-length covering, use braid or convoluted. Round jacket, use a cable.
Spiral wrap: we offer it, but braid or convoluted almost always wins. Its niche is frequent mid-run breakouts with easy re-entry.
Sizing notes
- Give the nominal bundle OD for each segment and the largest connector the covering must pass over.
- Size braid by its expansion range, not just the relaxed diameter.
- Choose loom by inside diameter and fill; leave room at bends and branches.
- Call out tape overlap and heat-shrink expanded/recovered diameter, adhesive-lined or plain.
Routing
Securing and branching
Spot-tie with zip ties or tape every 6 to 12 inches. Tie tension isn't worth obsessing over, but it should prevent sliding without flattening insulation. Use lacing, tape, cushioned ties, or clips where vibration, heat, abrasion, or bend radius matter. Branch with simple Y/T geometry from a trunk. Avoid octopus junctions; if a design seems to need one, change the breakout or move that section to a cable.
Rules of thumb
- 30 to 50 wires per bundle, then split.
- Cable to about 10 to 20 conductors; above that, bundle.
- Secure every 6 to 12 inches.
- Color-code the wires. Not all black.
- Common wire: TXL/GXL for automotive, silicone for heat/flex, UL1007/1061 for electronics, UL1015 for control wiring.
- Use simple Y/T breakouts from a trunk.
Handoff
Handing it to a manufacturer
The builder needs electrical intent and enough mechanical envelope to make the harness buildable. They do not need a brittle drawing that makes every splice land at the same coordinate.
- Use a cable where you can.
- Color-code the wire list.
- Design simple Y/T breakouts.
- Name splice connections, not coordinates.
- A drawing suits a complex design; a spreadsheet covers a simple one.
Minimum handoff package
- Connector part numbers, keying, and cavity map
- Wire gauge, color, insulation family, and net names
- Lengths, branch points, and tolerances
- Covering callouts by segment plus labels
- Splice netlist, not splice coordinates
- Mounting clips, strain relief, and test requirements
A good shop staggers splice locations along the run so the bundle stays slim instead of bulging at one point. If you require IPC/WHMA-A-620 acceptance, specify the class and acceptance requirements separately.
Or build it in our configurator and skip the formatting.
Related Guides
Keep the spec grounded
These pages cover adjacent decisions that usually show up while a harness is still cheap to change.
Custom wire harness assembly
Turn the cable-or-bundle decision into a buildable harness order.
Wire harness manufacturing guide
Materials, sleeves, splices, testing, and process context.
Shielded cable assembly
When EMI control matters more than hand-bundled flexibility.
Automotive wiring
Practical context for TXL/GXL wire, loom, heat, and vibration.
Next Step
Skip the formatting. Build it in the configurator.
Spec a harness in the configurator and it prices itself, or send a wire list and we'll quote it.
