View Latest Blog Entries
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Protection & Prevention Management Conference & Report Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR Electromagnetic Interference (EMI) AS4373 Maintenance FAR 25.1707 Wire System Arcing Damage
All Tags in Alphabetical Order
2021 25.1701 25.1703 abrasion AC 33.4-3 AC 43 Accelerated Aging accessibility ADMT Aging Systems AIR6808 AIR7502 Aircraft Power System aircraft safety Aircraft Service Life Extension Program (SLEP) altitude arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS23053 AS29606 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS6324 AS81824 AS83519 AS85049 AS85485 AS85485 Wire Standard ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D8355 ASTM D876 ASTM F2639 ASTM F2696 ASTM F2799 ASTM F3230 ASTM F3309 ATSRAC Attenuation Automated Wire Testing System (AWTS) Automotive Avionics backshell batteries bend radius Bent Pin Analysis Best of Lectromec Best Practice bonding Cable Cable Bend cable testing Carbon Nanotube (CNT) Certification cfr 25.1717 Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection cleaning clearance Coaxial cable cold bend collision comparative analysis Compliance Component Selection Condition Based Maintenance Conductor Conductor Testing conductors conduit Connector connector installation Connector rating connector selection connector testing connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) corrosion prevention Cracking creepage D-sub data analysis data cables degradat Degradation Delamination Derating design safety development diagnostic Dielectric breakdown dielectric constant Dimensional Life disinfectant Distributed Power System DO-160 dry arc dynamic cut through E-CFR electric aircraft Electrical Aircraft Electrical Component Electrical Power Electrical Testing Electrified Vehicles Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) Electrostatic Discharge EMC EMF EMI EN2235 EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling environmental stress ethernet eVTOL EWIS certification EWIS Component EWIS Design EWIS Failure EWIS sustainment EWIS Thermal Management EZAP FAA FAA AC 25.27 FAA AC 25.981-1C FAA Meeting failure conditions Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 Fault fault tree Filter Line Cable Fixturing Flammability fleet reliability Flex Testing fluid exposure Fluid Immersion Forced Hydrolysis fuel system fuel tank ignition Functional Hazard Assessment functional testing Fundamental Articles Fuse Future Tech galvanic corrosion Glycol Gold Gold plating Green Taxiing Grounding hand sanitizer handbook Harness Design harness protection hazard Hazard Analysis health monitoring heat shrink heat shrink tubing high current high Frequency high speed data cable High Voltage High Voltage Degradation HIRF History Hot Stamping Humidity Variation HV connector HV system ICAs IEC 60851 IEC60172 IEEE immersion insertion loss Inspection installation installation safety Instructions for Continued Airworthiness insulating material insulating tape Insulation insulation breakdown insulation resistance insulation testing interchangeability IPC-D-620 ISO 17025 Certified Lab ISO 9000 J1673 Kapton Laser Marking life limit life limited parts Life prediction life projection Lightning lightning protection liquid nitrogen lithium battery lunar Magnet wire maintainability Maintenance Maintenance costs Mandrel mean free path measurement mechanical stress Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 MIL-DTL-23053E MIL-DTL-3885G MIL-DTL-38999 MIL-E-25499 MIL-HDBK MIL-HDBK-1646 MIL-HDBK-217 MIL-HDBK-454 MIL-HDBK-516 MIL-HDBK-522 MIL-HDBK-525 MIL-HDBK-683 MIL-STD-1353 MIL-STD-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-7928/5 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 MIL–STD–5088 Military 5088 modeling moon MS3320 NASA NEMA27500 Nickel nickel plating No Fault Found OEM off gassing Outgassing Over current Overheating of Wire Harness Parallel Arcing part selection Partial Discharge partial discharge at altitude Performance physical hazard assessment Physical Testing polyamide polyimdie Polyimide-PTFE Power over Ethernet power system Power systems predictive maintenance Presentation Preventative Maintenance Program Probability of Failure Product Quality PTFE pull through Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Resistance Revision C Rewiring Project Risk Assessment S&T Meeting SAE SAE Committee Sanitizing Fluids Secondary Harness Protection separation separation distance Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure shelf life Shield Shielding Shrinkage signal signal cable Silver silver plated wire silver-plating skin depth skin effect Small aircraft smoke Solid State Circuit Breaker Space Certified Wires Splice standards Storage stored energy superconductor supportability Sustainment System Voltage Temperature Rating Temperature Variation Test methods Test Pricing Testing testing standard Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Runaway Thermal Shock Thermal Testing tin Tin plated conductors tin plating tin solder tin whiskering tin whiskers top 5 Transient Troubleshooting TWA800 UAVs UL94 USAF validation verification video Visual Inspection voltage voltage differential Voltage Tolerance volume resistivity vw-1 wet arc white paper whitelisting Winding wire Wire Ampacity Wire Bend Wire Certification Wire Comparison wire damage wire failure wire performance wire properties Wire System wire testing Wire Verification wiring components work unit code

Impact of Secondary Wire Harness Protection on Heating

Protection & Prevention

Key Takeaways
  • Wire harness ampacity (the maximum amount of current a wire harness can transfer without overheating) must be part of wire harness design.
  • Secondary wire harness protection materials are needed and they are a critical part of the EWIS
  • There is a thermal cost with the use of secondary wire harness protection.

If you are standing outside on a cold winter day, would you be warmer in a T-shirt or in a jacket? The answer is obvious, but somehow that ‘obvious answer’ is obscured when thinking of aircraft wire harness design. A common question of OEMs and aftermarket modifiers is: how much of an impact (if any) does secondary harness protection have on wire harness heating?

Lectromec took time this last week to put together a representative harness and run tests to generate data on the thermal impact of three secondary wire harness protection schemes. While this data is not representative of every wire harness configuration, it does provide a basis for determining if additional testing (or simulation) are needed for your application.


As electrical energy is transmitted down a wire, there is inherent resistance of the current carrier. This resistance leads to the wire/cable heating. With more current, the heating is more pronounced, and at some current level, the heating can exceed the temperature rating of the conductor and/or insulation.

For those interested in learning more about these ideas, Lectromec has several articles on the topic:

To take this idea one step further, not all wire harnesses are the same and depending on the function, location, and/or separation needs, some wire harnesses (or sections of wire harness) will need additional protection. Sometimes this protection is needed for physical protection (think chafe protection) or for electrical protection (think shielding for EMI). How this secondary protection impacts the temperature rise of a harness was the objective of these tests.

Test Setup

The test was setup with the following parameters:

  • 10x 20AWG (2ft harnesses) wires attached to a circuit set to carry 12A when at the ambient temperature of 23oC. As the wires heated, the current decreased as the conductor resistance increased. While this current level is over the typical rated current for the 20AWG wires (20AWG is typically coupled with a 7.5A circuit protection), it simply represents a system running warm.
  • The wires used were of wire specification AS22759/34 (tin plated copper conductor with XL-ETFE insulation).
  • One open and three secondary wire harness protection techniques were evaluated:
    • Open harness  
    • Nomex protected (Similar to EN6049-006 products)
    • Shielded harnesses (no other protection)
    • Shielded with Nomex on top

Thermal measurement was captured on the outside of one wire at the center of the wire harness. While it is typically recommended that the temperature is captured on the conductor, we chose to measure the temperature on the outside surface of one wire for expediency.

What Should be Expected?

Starting with the theoretical basis is always a good idea. Harness derating has been covered in past articles and this article will not delve into it (see list of articles above). Running the numbers through the AS50881 derating suggests that a single wire would have a temperature increase of about 40oC. With more wires thrown into the wire harness, there is a 50% derating factor and would place the temperature increase around 80oC. This temperature increase is the estimated temperature increase of the open harness wire conductor temperature; the measurement of the insulation temperature will be below this temperature increase.


Four different wire harness protection schemes were tested. The question: what would be the thermal impact of the testing?

The accompanying photos show the setup. Each harness was hooked up to the circuit in the same way in an open space and secured at both ends allowing the center of the harness to hang freely. The test power was applied, and the sample was left without interference for 15 minutes. The objective was to achieve equilibrium and the first test found equilibrium was achieved in less than 15 minutes. While at least one test was still trending upwards after 15 minutes, the comparison between the secondary protection types is still valid.

The graph below shows the impact:

  • Nomex protected: +50oC impact
  • Shielded harnesses (no other protection): +10oC impact
  • Shielded with Nomex on top: +30oC impact

The potential for the Nomex harness having the largest temperature increase may be due to the limited direct contact points between the wiring harness and the sleeving. In other words, the transfer of thermal energy from the wiring harness to the secondary harness protection was convection and radiation and only limited conduction. The shielded secondary harness protection does act as a good thermal conductor but appears to have the smallest thermal impact.

Impact of secondary harness protection on wire harness temperatures.

Knowing the temperature differential between the insulation temperature and conductor temperature, it is likely that the conductor far exceeded the 150C limitation of tin-plated wires. Long-term, this would likely result in degradation of the conductor and intermetallic growth.


The data presented here is not meant to dissuade anyone from using secondary protection if it is needed for their application; Secondary harness protection is a part of aircraft EWIS design. The intent is to provide data to enlighten users that there is an impact on the harness temperature.

The thermal impact of secondary wire harness protection is measurable and can be significant. The thermal conductivity and contact interface with the wire bundle will determine the thermal impact.

If you are looking for data on your wire harness configuration, contact Lectromec. We have the knowledge, experience, and lab capabilities to perform the tests you need.

Michael Traskos

Michael Traskos

President, Lectromec

Michael has been involved in wire degradation and failure assessments for more than a decade. He has worked on dozens of projects assessing the reliability and qualification of EWIS components. Michael is an FAA DER with a delegated authority covering EWIS certification and the chairman of the SAE AE-8A EWIS installation committee.