View Latest Blog Entries
Close
Categories
Testing & Assessment Certification Aging Wires & Systems Standard & Regulation Management Maintenance & Sustainment Conference & Report Research Protection & Prevention Arcing Miscellaneous
Popular Tags
Visual Inspection AS50881 MIL-HDBK MIL-HDBK-525 High Voltage FAR Electromagnetic Interference (EMI) FAR 25.1707 AS4373 Maintenance Wire System Arcing Damage
All Tags in Alphabetical Order
2021 25.1701 25.1703 abrasion AC 33.4-3 Accelerated Aging 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 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS83519 AS85049 AS85485 AS85485 Wire Standard ASTM D150 ASTM D8355 ASTM F2696 ASTM F2799 ASTM F3230 ASTM F3309 ATSRAC Attenuation Automated Wire Testing System (AWTS) Automotive backshell batteries Bent Pin Analysis Best of Lectromec Best Practice bonding Cable Cable Bend cable testing Carbon Nanotube (CNT) Certification Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection Coaxial cable cold bend collision comparative analysis Compliance Component Selection Condition Based Maintenance Conductor conductors conduit Connector connector selection connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) Cracking 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 Electrical Aircraft Electrical Component Electrical Power Electrical Testing Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) 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 tree Fixturing Flammability fleet reliability Flex Testing fluid exposure Forced Hydrolysis fuel system fuel tank ignition Functional Hazard Assessment functional testing Fundamental Articles Future Tech galvanic corrosion Glycol Gold Gold plating Green Taxiing Grounding hand sanitizer handbook Harness Design Hazard Analysis health monitoring heat shrink heat shrink tubing high current high Frequency high speed data cable High Voltage HIRF History Hot Stamping Humidity Variation HV system ICAs IEC60172 IEEE 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 liquid nitrogen lunar 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-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-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 polyimdie Polyimide-PTFE Power over Ethernet power system Power systems predictive maintenance Presentation 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 Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure shelf life Shield Shielding 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 supportability Sustainment System Voltage Temperature Rating Temperature Variation Test methods Test Pricing Testing 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 vw-1 wet arc white paper whitelisting 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

4 aspects of wiring selection for special aircraft applications

Protection & Prevention Standard & Regulation

Not all wires are created equal. Through the years, Lectromec has learned the best practices for wire selection that would ensure the Electrical Wire Interconnect Systems’ (EWIS) longevity.

There are thousands of wire standards for the aerospace industry. These include: the National Electrical Manufacturers’ Association (NEMA) standards, the Society of Automotive Engineers (SAE) standards, as well standards from military organizations commonly referred to as Military Specifications or MIL-Specs. Counting only those from the aerospace industry, there are more than a thousand standards, which do not even include the thousands of standards for the supporting equipment (connectors, splices, etc.). Each has a particular use, application, and properties. Each standard is intended to help manufacturers meet section 3.8.10 of the AS50881 requirements, for the purposes of wire selection for special applications within the aircraft. There are several areas of an aircraft that require special attention and equipment. Here we begin a discussion on four aspects of wiring selection for special aircraft applications.

SWAMP

Severe wind and moisture-prone (SWAMP) areas are areas of the aircraft, in which the electrical system has the greatest exposure to the elements. For these areas, most modern wire insulation types are acceptable, but consideration should be given to those wire constructions that offer better humidity resistance as well as mechanical strength.

Additional thought should be given to the protection of EWIS components. The FAA’s EWIS Job Aid provides some guidance as to what should be considered within these areas:

Environmentally‐sealed splices that conform to MIL-T-7928 provide a reliable means of splicing in SWAMP areas. However, a non‐insulated splice connector may be used, provided the splice is covered with dual wall shrink sleeving of a suitable material.

Flexing

One of the shortcomings of flex testing is that a simple continuity check will not be able to identify any issues, even when a wire may have several conductor strands broken due to flexing. This is due to the fact that a continuity check only looks for a conductive path for low current and voltage, which is well below the energy level that can cause damage to a single strand of conductor. Even a handheld multimeter is not sensitive enough to detect when most of the conductor strands are broken.

What this means is that, not only is it necessary to consider the fatigue on a wire, but also on the other EWIS components. For example, some of the components that may be overlooked in a flex prone application are the connectors. If not properly mounted and supported with strain relief the flexing of wire harnesses can place significant strain at the terminal locations. Regular flexing at these locations can dramatically reduce the component service life.

Tests like the AS4373 Method 704, look closely at the longevity of wires in flexing environments. By selecting those wire/cables with the best performance for this test, it is possible to extend the component service life.

Electromagnetic Interference (EMI)

(For an introduction to EMI, check out Lectromec’s article on how to deal with EMI and Electromagnetic Vulnerability (EMV) on Radio Frequency (RF) Cables for Aerospace Applications.)

There are some applications, in which an unshielded wire is acceptable for signal transmission. However, given the high voltages and signal rates for many applications, there is often a need to protect certain systems from EMI. These situations can be resolved with shielded cables such as those that are defined by several varieties of NEMA27500 cables or AS85485 wire standards. The type of cable shielding (coverage, number of shields) should be dependent on the signal sensitivity and system criticality.

Thermocouple Wiring

Thermocouple wiring is used as part of temperature monitoring circuits. Because these wires are specially made from two metals that produce a temperature dependent voltage, additional care must be taken with the routing and maintenance. For installation, the FAA’s Job Aid (referenced above) recommends that the bend radius of thermocouple wiring be not less than 20 times the diameter of the wire. Note that this recommended bend radius is significantly larger than the 6x for RF cables, and 10x for harnesses.

With regard to thermocouple wiring maintenance, splicing of thermocouple wiring is not recommended as this may impact the temperature reading. If splicing is necessary, there are splices in the AS85485 specification that are ideal for the task.

Summing it Up

While these part selection recommendations may sound straight forward, it took the combined effort of the aerospace industry to make them as comprehensive and useful as possible to the industry. When evaluating the best solution for a given installation, most of the time there is an existing solution. Using the right part for the right application will yield superior system performance and improved system reliability.

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. In September 2014, Michael was appointed as an FAA DER with a delegated authority covering EWIS certification.