View Latest Blog Entries
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Management Conference & Report Protection & Prevention Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR AS4373 Maintenance Electromagnetic Interference (EMI) 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 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 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 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 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
Key Takeaways
  • There are test methods to assess the performance of wires/cables in overload conditions.
  • Time/Current to Smoke increases the current until smoke is observed. Smoke resistance increases the current until the conductor reaches a target temperature.
  • Both of these tests provide insights necessary for the next generation of more electric aircraft (MEA).

Several things can go wrong when a wire or cable is subjected to an electrical current exceeding its design limitation and none of them are good. These include, but are not limited to, melting of the insulation, smoking, insulation degradation, promotion of intermetallic growth between the plating and conductor, melting of the conductor, melting of the conductor plating, and conductor embrittlement. Thankfully, if the wire/cable is being used within its temperature and current ratings, the wire should experience very little of the above phenomena.

Often, it is the wire insulation that is most vulnerable. Smoking of the insulation is one of the most common failure modes and it is hard to identify unless the wire is closely monitored during the event. For this reason, some of the aerospace industry’s high current tests seek to determine the susceptibility and conditions necessary to achieve these hazardous conditions.

Tests like the smoke resistance (AS4373 method 513) and Time/Current to Smoke (AS4373 method 507) are just a couple of these tests. One might ask why there are two separate and seemingly similar test methods. One difference comes down to the scope of the standards, another is the specifics and aim of the test methods.

Wire and Current Overcurrnt
Most wires can hold more than 2x their current rating for an extended duration before giving off smoke. In this example, a 8AWG wire hanging free in air is able to carry more than 250A before showing any signs of smoke.

Time/Current to Smoke

The Time/Current to Smoke test increases the electrical current through the sample at given increments (e.g. 5A every 30 seconds) until the wire smokes. The time and current at which the smoking is observed are reported. As a result, this test gives an understanding of the overload conditions at which the wire is known to fail. From an application perspective, this means that the wire should not be used at or in excess of the current level identified in the test. This is a useful factor in EWIS design as it provides a threshold for performance and input on circuit protection selection.

The test standard applies to a limited wire gauge range (wire smaller 16 AWG and smaller) and this is most likely due to its specified current level increases. If performed on larger gauge wires, the current step levels can be increased to complete the test in a reasonable time.

Overcurrent effects on wire
Over-current conditions will damage conductors and wire insulation. Do not assume that no visual damage means no damage.

Smoke Resistance

Smoke resistance is a newer test method made to accommodate larger wire gauges and to certify that the wire will operate at specified conductor temperature limits without generating any smoke. In this test, the wire conductor current is increased slowly until the wire conductor stabilizes at the specified temperature (this temperature is either at the wire’s rated temperature or 30oC higher). The current level is monitored and adjusted so that the wire conductor stays at the specified temperature for 15 minutes.

This is a pass/fail test that gives assurance that a wire’s construction will operate effectively at the top of its rated current/temperature range. In addition, the smoke resistance test is applicable to a wider array of wire sizes. This requires greater current sourcing capabilities to run the test on large wire gauges.

Figure 1 shows the current and temperature profile of a 22759/34-8AWG specimen. For demonstration purposes, the current was increased well passed rated temperature limits. This data shows the worst-case scenarios for gross failure. Properly designed circuitry and circuit protection will cut off power to the circuit long before these types of gross failures occur.


The Time/Current to Smoke and Smoke Resistance tests are not tests that exist solely for wire/cable verification but are a critical element in high-performance EWIS design. If the industry is to push the electrical system to design limits and maximize the ampacity of each wire and wire harness, then this information cannot be set aside and forgotten.

Tristan Epp Schmidt

Tristan Epp Schmidt

Engineer, Lectromec

Since starting at Lectromec in early 2015, Tristan has been key in many of test and assessment wire systems assessment projects wire systems assessment. His attention to detail has lead to several key insights in Lectromec’s research initiatives.