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 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 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 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

Voltage, Current, and Thermally Rating Connectors

Testing & Assessment

Key Takeaways
  • Comprehensive evaluation of connector voltage capability requires considerations of parameters such as partial discharge and altitude in addition to standard voltage application.
  • The current rating of both the individual contacts and the connector as a whole must be considered when determining connector current rating.
  • Testing of connectors for a specific application should be representative of the intended application.

While electrical component qualification is nothing new to the aerospace industry, the emerging trend toward full aircraft electrification requires every component to be electrically connected; for most equipment, this means incorporation of electrical connectors. Weight, cost, reliability, and performance are the four most common elements initially considered in connector selection, but the finer details of electrical connectors use must also be considered. Here, we discuss how one might go about qualifying an electrical connector, specifically, to address its voltage, current, and thermal limitations.

Where to Start

The best starting point to define these parameters is with the MIL-DTL-38999 and AS39029 standards (the MIL-C-39029 has been moved to the SAE – you can still get an old copyright-free version). For those unfamiliar, the MIL-DTL-38999 has been an industry standard for decades and has impacted electrical connector design for aerospace vehicles for generations. This is a good starting point to learn about standard tests that are required for generalized aircraft connectors.

Many of the stressor tests (environmental, thermal, etc.) have parameters that can be considered excessive for benign aircraft environments. After all, these are military specification connectors and are expected to work in harsh environments. As such, those applying these tests to more benign conditions should look to align the test parameters for the intended application.


Physical Failure Assessment Branch
Connector test voltages (Table III from MIL-DTL-38999) .

Section of MIL-DTL-38999 elaborates on voltage rating. The provided table shows the test voltages for both mated and unmated connectors. The expectation is that the test should identify any “disruptive discharge”. For those familiar with Lectromec’s articles on high voltage, there are two threat modes for partial discharge: through the material or on the surface.

Consideration of Functionality

Beyond standard voltage application on the connectors is also important when selecting connectors. The test methods identified in MIL-DTL-38999 are focused on lower voltage systems, specifically, those below 300 volts. Above 300 volts, factors such as partial discharge need to be considered and should be assessed during the voltage application in testing. If partial discharge is not measured during the test, and only the leakage current between two pins (or pins and shell) is captured, test results may yield an incorrect safe operational voltage assessment for the connector.

Because the connectors are used for aerospace applications, testing at reduced air pressure is important. As can be seen from the included table, the test voltage of an unmated connector drops by more than 50% for every connector type when tested at 50kft relative to its sea level test voltage. The performance change can be dramatic, and a factor worthy of determining through testing. For further information on how altitude can impact partial discharge, see this article.

Furthermore, the type of voltage applied can impact performance. In application, if different voltage waveforms beyond AC are used, such as high frequency or pulse width modulation, this may impact the connector longevity. From a general test and performance perspective, this risk of impact may limit the actual test application to just 60 Hertz; in such a case, the deviations from the standard testing voltage should be identified in the product specification. For the specific application, testing should be carried out to verify performance with the operational voltage/ frequency and include vehicle environmental and electrical factors such as electrical transients (voltage spikes), temperature, and altitude.

Connector Current Rating

Consideration of connector current rating can be broken down into two parts: the current rating of the contact and the current rating of the connector as a whole.

Tests in AS39029 evaluate the current rating of the contact. Testing primarily consists of a progressive increase in current on the contact under test until the maximum temperature is attained.

As with any other property, the current rating of the connector can become more complicated as the number of powered circuits can impact this. The effort of testing all circuits on a connector with up to five contacts may be relatively simple, but quickly becomes impractical as the number of contacts in a connector increases.

The connector current rating quickly becomes a very difficult thermal energy problem with several factors to consider:

  • Where the current is flowing through the contacts,
  • The contact sizing,
  • The thermal transfer to the connector inserts,
  • The thermal transfer to the connector shell,
  • The equipment to which the connectors are mounted,
  • The thermal transfer down the wires and cables that are connected to the connector,
  • Air flow,
  • Material properties of every relevant piece of equipment,
  • Ambient temperature conditions, and
  • Static and dynamic electrical loads

These all have an impact on the maximum current that can be carried by the connector. There is not a standard formula that has been able to capture all of these factors like those in AS50881 for wire bundle current derating. The most effective way to gather the electrical limits is to spend a day or two in the lab to generate the data.

5-pin connector configs
Configurations for 5-pin connectors

Consider the possible electrical load tests for a single 5-pin connector. To simplify the number of possible configurations, the example shall only consider:

  • Connectors with more than one populated pin always have pin ‘A’ populated.
  • Does not consider pins that are populated but unpowered.
  • Assumes that all powered circuits have the same current.

Even with these simplifying assumptions, there are 20 potential configurations. It is possible that most of the similar configurations will yield similar results. If the temperature increases in the connector does not come close to the maximum temperature rating, simplifying assumptions can be employed. However, as the design gets closer to the maximum temperature, the test will have to represent electrical and environmental conditions more closely.


Temperature rating is handled typically by looking at the weakest part of the connector construction (thermally) and setting the maximum temperature below that. The limit might be based on plating, adhesive, mechanical performance, etc. If there is no data, then thermal tests should start with an educated guess and increase or decrease the exposure temperature based on the connector performance in thermal shock or thermal cycling tests.

The pass criteria for the thermal cycling test gives general requirements on the post-exposure connector condition. The MIL-DTL-38999 states that, “there shall be no blistering, peeling or separation of plating or other damage detrimental to the operation of the connector.” Elements like discoloration and superficial damage are acceptable; changes to pin-to-pin resistance, for example, may suffer some degradation and that level of degradation may require additional testing and longer duration thermal exposure to understand the severity of the performance change.

The Intended Application

When setting performance levels of any of the tests discussed here, it is important to avoid creating overly severe test conditions to “see if it will fail”. If the goal is for the connector to be qualified for the general case, then this approach may require multiple test iterations, but will generate data to support the performance claims.

However, if the intended application is narrower and intended to be limited to a single aircraft or system, then the test parameters should align with the vehicle performance requirements. This objective creates different drivers on the test plan development that will push the connector to be tested below its performance capabilities, however, this reduces the potential of poor test results leading to redesign.


The voltage, current, and thermal parts of connector qualification are straight forward, but they do require some thought and planning before being implemented. In many cases, particularly with non-standard (i.e., non-60Hz and elevated voltage) power systems, there will be practical limitations as to how much testing can be performed by a supplier. The range of actual applications and systems the connector might be attached to is limitless and this means that due diligence is needed by the system integrator to ensure the connector, and wiring system, can meet the performance requirements.

For those that need help in connector assessments, whether it is getting started, testing, or analysis, Lectromec’s team of wiring system specialists is here to help. Contact us to set up a time for a discussion.

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.