Proper EWIS design can ease the process of maintenance
What makes NASA so successful in its missions? A key factor is its practice of regular documentation, which includes how to address various issues that can include Electrical Wiring Interconnection Systems. Although this can add time and cost when first implemented, this practice can provide an excellent training resource for new hires and reduce the time from problem identification to resolution.
NASA has a tremendous portfolio of challenging and ultimately successful missions and their work and experience yield several excellent recommendations for many aerospace EWIS applications. This is the second edition of Lessons Learned from NASA (first article).
1. Splicing of Electrical Cables/Adding Connectors
- Suggestion: When designing and installing electrical cables, they should be of sufficient length to allow for future maintenance. Cutting electrical cables and subsequent reconnection by splicing may become necessary and it is important to provide adequate slack.
- Advantage: If the electrical cable is not long enough, splicing may critically reduce its length and may increase the probability of cable malfunction or require the entire wire length to be changed (many maintenance guidelines limit the number of repair splices to just one). Additionally, allowing sufficient slack decreases the likelihood of placing additional strain on the spliced wire.
- Source: http://llis.nasa.gov/lesson/313
2. Wiring Harness Connectors and Installation
- Suggestion: An aircraft’s wiring harness connectors should be suitable to endure vibration-induced stresses. Identifying the capability of connectors is critical. Improving quality review and testing are also good practices.
- Advantage: Connectors with sufficient protection from sharp edges and abrasive surfaces are less likely to experience wire damage due to flight vibration. This practice will also increase the life expectancy of the wiring harness, increasing cost effectiveness.
- Source: http://llis.nasa.gov/lesson/50
3. Electrical Connector Retest
An aircraft uses thousands of electrical connectors to allow rapid connection and disconnection of electrical circuits for maintenance, modification, inspection, and troubleshooting.
- Suggestion: Due to new technologies, it is recommended to increase the use of serial digital buses, which reduces the number of discrete circuits and improves design.
- Advantage: The built-in ability to retest the circuit precludes the need for manual activation of hardware. The use of serial buses reduces both connector and wire weight.
- Source: http://llis.nasa.gov/lesson/3759
4. Assembly Drawings of Electrical Cables
- Suggestion: Assembly design and process planning should be complete and clear and include detailed instructions. One way to ensure that the design plan is coherent is to test it. At least two different technicians should be able to easily perform the required assembly process.
- Advantage: Installation is easier and any changes or repairs can be performed in less time. Additionally, future issues related to poor maintenance may be averted.
- Source: http://llis.nasa.gov/lesson/3759
5. Control of Temporary Wire Installation
A wire harness fit check ensures that the wire harnesses will fit in a particular area of an aircraft or spacecraft. Temporary wire harnesses are installed and should be replaced for the vehicle’s final design.
- Suggestion: It is critical to flag the temporary wire harness. In 1988 NASA faced this issue when the subsequent manufacturing operations were continued through several steps before they realized that the wires were meant to be replaced, causing a delay in production.
- Advantage: Documenting and removing all temporary wire harnesses when the final design is complete can save time and money.
- Source: http://llis.nasa.gov/lesson/1258
These are just a few of the suggestions from NASA’s excellent lessons learned database. Any aerospace Original Equipment Manufacturer (OEM) or harness manufacturer in the prototyping stage should consider reviewing the accumulated lessons learned from NASA. It is critically important to consider all aspects of wiring before product delivery. For more information on these topics, visit NASA’s website at http://llis.nasa.gov/search?q=wire.
Omid Orfany
Electrical Engineer, Lectromec
info@lectromec.comOmid is an EE with a background in electrical system design and analysis. Since he started with Lectromec, Omid has worked on a variety of projects including wire failure assessment, equipment design, and EWIS degradation.