View Latest Blog Entries
Close
Categories
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 Circuit Protection
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 Aluminum arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Resistance 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 B230 ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D495 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-F-5372 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
Key Takeaways
  • A splice is a metal ferrule that is crimped to an incoming wire conductor on one side and crimped to an outgoing wire on the other side.
  • Though useful in repairs and modification, overuse of splices can lead to serious electrical and mechanical problems in an electrical system.
  • Restrictions on the use of splices on aircraft must be followed to ensure safety of the system.

Splices are a commonly implemented means of joining circuits. They provide an easy and reliable means to join two wires and can be done with minimal tooling. It is important however that the restrictions for the use of splices are followed to ensure a safe and reliable aircraft wiring system; improper use can have a direct impact on system performance and failures that have both physical and functional impacts.

Fundamentals

First and foremost, what is a splice? A splice is a metal ferrule that is crimped to an incoming wire conductor on one side and crimped to an outgoing wire on the other side. While there are numerous varieties of splices that do include configurations allowing for multiple wires to be spliced, such as necessary for data cables, at the core design, the wire splice is about joining two conductors together. This may be done for a variety of reasons such as:

  • Replace damaged sections of wire,
  • Support the installation of new or modified equipment,
  • Extend the length of a wire to facilitate repairs and maintenance, and
  • Support production breaks in harnesses fabrication.
Splice Anatomy
Example of a MIL-T-7928/5 aviation splice.

The diagram for a MIL-T-7928/5 splice is shown here. Notable features include:

  • Inspection window to identify that the conductors are fully inserted.
  • Insulation sleeving that extends beyond the end of the ferrule to protect the conductive members. The sleeving is wider than the metal ferrule making it possible to still have wire insulation under the splice.
  • Locator window that typically consists of a transparent or translucent portion in the insulation or housing of the splice, allowing technicians or inspectors to visually confirm that the wires are properly inserted, aligned, and securely connected within the splice enclosure. This feature enhances the efficiency and reliability of wire splicing operations by enabling quick visual checks for quality assurance and troubleshooting without the need for specialized tools or dismantling of the splice.
  • A wire stop to prevent an inserted wire from going beyond the midpoint of the splice.
Cold Splices
The cold splices shown here provide maintainers additional options for aircraft electrical wiring system sustainment activities. It is important to recognize that this may not be the ideal solution for all scenarios and has a maximum operational temperature around +165oC.

The AS81824 splices, transferred from the MIL-S-81824, are a class of aerospace-grade splices designed to be environmentally sealed; the splice insulation is heat shrink tubing allowing for compression of the insulation around the wire insulation. Furthermore, the AS81824 splices are designed for single wires and coaxial cables, and options exist for both heat sealing of the splice and cold seals for areas that are harder to maintain due to space constraints preventing the use of a heat gun.

Restrictions

When considering the use and installation of splices on aircraft, there are dozens of restrictions to ensure that the splices do not degrade the circuit performance or the mechanical integrity of the wiring. Ideally, splices are to be avoided as each cut, crimp, and termination of a circuit adds the potential for damage. Even with the best environmental seal on a splice, each creates an opportunity for fluid ingress. Furthermore, splices weaken the mechanical strength on the wiring segment. A factor that is often overlooked: smaller gauge wires (smaller than 20AWG) will frequently have the mechanical strength carried by the insulation, not the conductor. This means that, for splices of smaller gauge wires, there is a greater chance that the mechanical strength will be negatively impacted as the insulation is removed and the conductor is used to carry any mechanical stress.

Staggered Splices
Splices in bundles must be staggered so as to minimize any increase in the size of the bundle, preventing the bundle from fitting into its designated space, or cause congestion that will adversely affect maintenance.” 43.13-1B

First, it is a good design practice to limit the number of splices in each wire segment between two connectors or termination devices. Ideally, this number should be no greater than one. Again, the rationale for this is that for every splice added to a circuit, the mechanical performance the grades, the flexibility decreases, new failure points are added to the circuit, and potentially additional electrical degradation with increased voltage drop along the circuit. The solder splices are the exception as they are used to connect cable shielding with the connector shell.

Ideally, splices should not be part of primary power distribution and there are a couple of reasons for this. One, primary power distribution carries a lot of power and any additional resistance in the circuit may lead to premature degradation due to heating at the splice point. Second, the primary power distribution is a critical part of an aircraft’s electrical system and as discussed earlier, the addition of splices can reduce the reliability of the circuit.

Clamps

Wherever possible, splices should not be placed under any mechanical clamps. Consider the physical configuration of a wire harness under a clamp; a wire bundle is usually compressed a little bit and deformed due to the clamp grommet pressure onto the wire harness. Where this becomes an issue with splices is that the mechanical stress on the splice may manifest in a couple of ways:

  1. Push the edges of the splice into other wires within the wire harness; this can result in a stress point on the wire insulation and result in premature damage and degradation of other wires in the wire bundle.
  2. Cause additional mechanical stress on the spliced wire’s conductor which again should be avoided.

Flex Applications

Not installing splices into sections of wire that are in dynamic flex areas is perhaps the most obvious location-specific prohibition for splices. As splices tend to be more rigid, the installation of one created an unbendable section of the wire. This results in additional mechanical stress on the conductor at the crimp joint, additional stress on the wire at the ends of the splice, and likely results in a premature failure of the wiring in this location. If a wire needs to be repaired in such a location, then there are two options:

  1. Replace the wire entirely. While this is not ideal from a labor and materials perspective, it is the best option in many cases to ensure long-term reliability.
  2. Splice the wire outside of the flex area. This does mean that there will be two splices in the wire segment, but this does allow for a section of wire to be repaired and prevents the splice from being installed in the flex area. This option is not recommended as a long-term solution as there is a recommendation from AS50881 to limit the number of splices to no more than 1 per segment.

The Last Word

Splices are a key part of wiring systems as they provide solutions for forking circuits, distribution, connecting production harnesses at logical fabrication locations, and repair/maintenance. As with other parts of the wiring system, the use of splices requires the use of the right part, in the right place, under the right conditions, and installed with the right tools; each one of these factors requires time and attention to detail.

For those looking to test and/or assess the splices going into their electrical system, contact Lectromec. Our team of wiring system specialists working in our ISO 17025:2017 accredited lab are ready to help.

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.