{"id":205,"date":"2026-06-24T07:09:51","date_gmt":"2026-06-24T07:09:51","guid":{"rendered":"https:\/\/blogs.lcsccable.com\/blog\/?p=205"},"modified":"2026-06-24T07:09:51","modified_gmt":"2026-06-24T07:09:51","slug":"how-to-spec-a-wire-harness-for-manufacturing","status":"publish","type":"post","link":"https:\/\/blogs.lcsccable.com\/blog\/how-to-spec-a-wire-harness-for-manufacturing\/","title":{"rendered":"How to Spec a Wire Harness for Manufacturing"},"content":{"rendered":"

A harness specification that omits conductor de-rating, connector retention force, or shield termination method produces assemblies that pass inspection but fail in the field. This guide translates electrical requirements into unambiguous manufacturing drawings \u2014 covering conductor sizing, bundle de-rating, insulation selection, shielding type, and crimp quality criteria \u2014 so contract manufacturers<\/a> build exactly what the design demands.<\/span><\/p>\n

Key Takeaways<\/span><\/b><\/h2>\n\n\n\n\n\n\n\n
#<\/span><\/b><\/td>\nKey Takeaway<\/span><\/b><\/td>\n<\/tr>\n
1<\/span><\/b><\/td>\nGauge governs temperature rise: <\/span><\/b>A conductor one AWG size undersized raises resistive power dissipation by ~26%, adding 8\u201312\u00b0C of temperature rise in a bundled harness \u2014 enough to halve insulation life per the Arrhenius model.<\/span><\/td>\n<\/tr>\n
2<\/span><\/b><\/td>\nBundle de-rating is non-optional: <\/span><\/b>IEC 60364-5-52 and NEC 310.15(B)(3)(a) mandate ampacity de-rating beyond three bundled conductors; a 9-conductor bundle at 40\u00b0C ambient reduces rated ampacity by 70%.<\/span><\/td>\n<\/tr>\n
3<\/span><\/b><\/td>\nContact resistance drives long-term reliability: <\/span><\/b>Tin-plated contacts start below 5 m\u03a9; unplated contacts in high-vibration environments can exceed 50 m\u03a9 after 500 thermal cycles, producing millivolt-level offsets in precision sensor lines.<\/span><\/td>\n<\/tr>\n
4<\/span><\/b><\/td>\nShielding must be specified, not assumed: <\/span><\/b>Foil (100% coverage) provides 30\u201340 dB at 10 MHz; braid at 85% yields 20\u201325 dB \u2014 a 10 dB gap separating CISPR 25 Class 5 compliance from non-compliance on CAN bus lines.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

What Is a Wire Harness<\/a>?<\/span><\/b><\/h2>\n

A wire harness is a pre-assembled group of electrical conductors, connectors, and protective sleeving forming a discrete wiring sub-assembly installed as a unit into a larger system. Unlike loose wiring, a harness routes, protects, and terminates all conductors in a single inspectable unit \u2014 which is why every parameter must be captured on the drawing before manufacturing begins.<\/span><\/p>\n

Internal Construction and Materials<\/span><\/b><\/h3>\n

A harness consists of stranded or solid copper conductors with PVC, XLPE, or PTFE insulation, bundled with spiral wrap or braided sleeving, and terminated with crimped connectors. Strand count is the first variable to specify for any moving harness: stranded 20 AWG with 19 strands achieves a flex life above 200,000 cycles per UL 758, versus fewer than 10,000 cycles for the equivalent solid conductor under the same conditions.<\/span><\/p>\n

Why Wire Harness Specification Is Indispensable for Engineers<\/span><\/b><\/h2>\n

A harness specification bridges electrical design and manufacturing process. Without it, contract manufacturers make undocumented substitutions \u2014 replacing XLPE with PVC on a high-temperature run, or fitting a lower-retention connector \u2014 that cause field failures invisible at assembly inspection. Every substitution a CM makes without documentation is a liability gap in the design record.<\/span><\/p>\n

What Are the Key Specification Parameters for a Wire Harness?<\/span><\/b><\/h2>\n\n\n\n\n\n\n
Parameter<\/span><\/b><\/td>\nDescription<\/span><\/b><\/td>\nEngineering Benefit<\/span><\/b><\/td>\n<\/tr>\n
Conductor ampacity with bundle de-rating<\/span><\/b><\/td>\nCurrent-carrying capacity per AWG\/mm\u00b2, corrected for the number of bundled conductors and ambient temperature per IEC 60364-5-52<\/span><\/td>\nPrevents insulation degradation from over-temperature; defines safe operating current for the full thermal environment<\/span><\/td>\n<\/tr>\n
Insulation temperature and dielectric strength<\/span><\/b><\/td>\nContinuous operating temperature (105\u00b0C XLPE, 70\u00b0C PVC) and dielectric withstand per UL 758 or IEC 60811<\/span><\/td>\nEnsures the harness survives the thermal and voltage environment without insulation breakdown over the service life<\/span><\/td>\n<\/tr>\n
Connector retention force and mating cycle rating<\/span><\/b><\/td>\nAxial retention force (N) per IEC 60512-6-2<\/a>; 30 cycles (industrial) or 250 cycles (field-serviceable)<\/span><\/td>\nGuarantees the connector withstands vibration and repeated servicing without contact fretting or retention loss<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

How Conductor Gauge Selection Impacts System Thermal Performance<\/span><\/b><\/h3>\n

Resistive power dissipation equals P = I\u00b2 \u00d7 R, where R for 20 AWG copper is 33.3 m\u03a9\/m at 20\u00b0C. In a bundled harness, heat cannot dissipate freely: stepping from 20 AWG to 18 AWG reduces resistance by ~37%, cutting dissipated heat proportionally and extending insulation life by a factor of two at continuous rated current per the Arrhenius degradation model.<\/span><\/p>\n

What Are the Critical Technical Specifications to Define?<\/span><\/b><\/h2>\n\n\n\n\n\n\n\n\n\n\n
Parameter<\/span><\/b><\/td>\nPower \/ Signal Harness<\/span><\/b><\/td>\nHigh-Flex \/ Automotive<\/span><\/b><\/td>\nUnit<\/span><\/b><\/td>\nStandard<\/span><\/b><\/td>\n<\/tr>\n
Conductor cross-section<\/span><\/td>\n0.5\u201310.0<\/span><\/td>\n0.35\u20132.5<\/span><\/td>\nmm\u00b2 (AWG 20\u201310)<\/span><\/td>\nIEC 60228 Class 5; SAE J1128<\/span><\/td>\n<\/tr>\n
Insulation rated temperature<\/span><\/td>\n70\u00b0C (PVC) \/ 105\u00b0C (XLPE)<\/span><\/td>\n125\u00b0C (XLPE-A); 150\u00b0C (ETFE)<\/span><\/td>\n\u00b0C continuous<\/span><\/td>\nUL 758; JASO D618<\/span><\/td>\n<\/tr>\n
Voltage rating (insulation)<\/span><\/td>\n300 \/ 600 V AC rms<\/span><\/td>\n60 \/ 600 V AC rms<\/span><\/td>\nV AC rms<\/span><\/td>\nUL 758; LV 112<\/span><\/td>\n<\/tr>\n
Shielding attenuation<\/span><\/td>\n30\u201340 dB (foil, 100%)<\/span><\/td>\n20\u201325 dB (braid, 85%)<\/span><\/td>\ndB at 10 MHz<\/span><\/td>\nCISPR 25; MIL-DTL-17<\/span><\/td>\n<\/tr>\n
Connector contact resistance<\/span><\/td>\n<5 m\u03a9 (tin, new)<\/span><\/td>\n<15 m\u03a9 (after 500 cycles)<\/span><\/td>\nm\u03a9<\/span><\/td>\nIEC 60512-2-1<\/span><\/a><\/td>\n<\/tr>\n
Minimum bend radius (flex)<\/span><\/td>\n10\u00d7 OD (static)<\/span><\/td>\n6\u00d7 OD (dynamic flex)<\/span><\/td>\n\u00d7 cable OD<\/span><\/td>\nIPC\/WHMA-A-620; SAE J1128<\/span><\/td>\n<\/tr>\n
Flame rating<\/span><\/td>\nUL 94 V-0 (sleeving)<\/span><\/td>\nFMVSS 302 (automotive)<\/span><\/td>\n\u2014<\/span><\/td>\nUL 94; ISO 6722<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

How Do These Specifications Affect Real-World Performance?<\/span><\/b><\/h3>\n