View Latest Blog Entries
Testing & Assessment Certification Aging Wires & Systems Management Standard & Regulation Conference & Report Maintenance & Sustainment Protection & Prevention Research Arcing Miscellaneous
Popular Tags
Visual Inspection MIL-HDBK MIL-HDBK-525 AS50881 FAR High Voltage FAR 25.1707 Electromagnetic Interference (EMI) Maintenance Wire System Arcing Damage FAR 25.1709
All Tags in Alphabetical Order
25.1701 25.1703 Accelerated Aging ADMT Aging Systems Aircraft Power System Aircraft Service Life Extension Program (SLEP) arc damage Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS83519 AS85485 AS85485 Wire Standard ASTM D150 ASTM F2799 ATSRAC Attenuation Automated Wire Testing System (AWTS) batteries Bent Pin Analysis Best of Lectromec Best Practice bonding Cable cable testing Carbon Nanotube (CNT) Certification Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection Coaxial cable cold bend comparative analysis Compliance Component Selection Condition Based Maintenance Conductor conduit Connector connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) Cracking D-sub data analysis data cables degradat Degradation Delamination Derating diagnostic dielectric constant Distributed Power System DO-160 Electrical Aircraft Electrical Component Electrical Testing Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) EMC EMF EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling ethernet EWIS Component EWIS Design EWIS Failure EWIS Thermal Management EZAP FAA AC 25.27 FAA AC 25.981-1C 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 testing Fundamental Articles Future Tech Green Taxiing Grounding Harness Design Hazard Analysis health monitoring heat shrink tubing high current high Frequency high speed data cable High Voltage History Hot Stamping Humidity Variation ICAs IEC60172 Instructions for Continued Airworthiness Insulation insulation resistance IPC-D-620 ISO 17025 Certified Lab Kapton Laser Marking life limited parts life projection Lightning Maintenance Maintenance costs Mandrel 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-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 Military 5088 modeling MS3320 NASA NEMA27500 No Fault Found off gassing Outgassing Overheating of Wire Harness Parallel Arcing part selection Performance physical hazard assessment Physical Testing polyimdie Polyimide-PTFE Power over Ethernet Power systems predictive maintenance Presentation Probability of Failure Product Quality Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Rewiring Project Risk Assessment SAE Secondary Harness Protection Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure Shield Shielding signal cable silver plated wire smoke Solid State Circuit Breaker Space Certified Wires Splice stored energy supportability Sustainment Temperature Rating Temperature Variation Test methods Test Pricing Testing Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Shock Thermal Testing Tin plated conductors Troubleshooting TWA800 UAVs verification Visual Inspection voltage white paper whitelisting Wire Ampacity Wire Certification Wire Comparison wire damage wire failure wire properties Wire System wire testing Wire Verification work unit code

A common question when it comes to designing an aircraft EWIS is which of the cables should be shielded? There are several standards, such as MIL-STD-461, “Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment” provide an excellent basis for topics and testing that should be considered. But for those that are not interested in reading a 280-page standard, this article reviews the several shielding considerations that should be made before making particular design choices.

Why Shield?

The quick and simple answer to why use shielding is to limit the impact of Electromagnetic Interference (EMI) on system performance. But just because EMI is a concern does not mean that shielding should be used on wiring from every system. The consequences of selecting a shielded cable construction include increased bend radius, increased weight, and increased installation/repair time. For those interested, we have covered the common shielding types in another article.

There are a couple of options when protecting systems from EMI and implementing shielding. These options include: shielding only the signal wires, shielding only the power wires, and shielding both. Each of these is reviewed here.

Shield Signal Wires

The starting point for many engineers and EWIS designers is to limit the potential EMI impact on signal cables. After all, these cables, which send signals with low voltages (often less than 10V) at high data speeds, can be negatively impacted by the electrical noise of aircraft equipment. Protecting the integrity of signals thus improves the confidence in the data integrity.

Wire EMI animation
How far away does your wire/cable need to be to avoid the impacts of EMI? This is a difficult question to answer because of all of the factors impacting EMI. Shielding can be a easier solution.

Of course, once the signal wires are identified for EMI protection/shielding, the question then goes to whether the individual wires/pairs should also be shielded if inside a multiconductor cable. The selection is dependent on the data rate (high frequencies generate more EMI and are more susceptible to EMI). With shielding a cable, then the internal pairs, the outer shielding can be a generalized shield and the internal shield can be optimized to shield the frequencies likely to be carried by the internal wires.

The benefits of shielding the signal wires:

  • Transmitted data for each system is isolated
  • If improved EMI protection is needed, it can be implemented system by system
  • Conceptually easy to address and plenty of available shielded cable options

Shield Power Wires

Another perspective is to shield the power wires. A typical aircraft design will have a larger percentage of signal wires than power wires, and thus it can be easier to shield the power wires.

When considering the latest trends with electrical power systems, there are several systems which gain equipment control with the use of pulse width modulation and wide frequency power generation. Each of these systems have benefits from the perspective of power and control, but create new challenges for EMI. Certainly, the use of pulse width modulated power with high-frequency current changes (dI/dt) can generate strong Electromagnetic Flux (EMF) and impact nearby signal wires.

The benefits of shielding the power wires:

  • Reduce the EMI sources throughout the aircraft
  • Possible overall aircraft EMI reduction thus reducing noise for sensitive electronic equipment
  • Additional chafe protection for power cables.

Shield Both

Looking to Determine the Effectiveness of Shielding?

Here are a couple of tests that you may wish to consider:

Another option is to shield both which provides the benefits of both; however, it comes with significant weight penalty. There are solutions that exist for reducing the overall weight burden of shielding, but there will always be a financial and weight cost for shielding. The difficulty with implementing this solution is that many of the harnesses become Line Replaceable Units (LRUs) and not designed for field maintenance. Naturally, the argument here is the if you can increase the reliability of a wire harness by a factor of 2 (as an example, no data to support), would you be willing to remove the field serviceable capability?


The use of shielding to protect wiring and signals has been around for generations, but with the modern aircraft design, the importance of protecting signal integrity is more important. There are multiple strategies for accomplishing this, and the implementation of shielding is entirely dependent on the performance requirement and the operation frequencies of the signal equipment.

In the end, it comes down to what design choice can create the most safe EWIS design capable of completing the prescribed task. To find out more about how to improve your EWIS assessments and EWIS safety, contact Lectromec.

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.