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AS50881

Aerospace High Voltage Systems: Addressing the Gaps in Current Standards

The aerospace segment has been dealing with questions of high voltage systems for the last decade. Many of these questions revolve around the generation, storage, and use of this power, but what has also been a hindrance for progress is defining how the standards for the wiring system need to be updated to address these high voltage requirements. As should be done when any new technology is being applied to a field, we should first look at other fields which have undergone the implementation of similar technologies. For example, the automotive market has been using high voltage systems for quite some time and the standards committees have produced documents supporting these technologies.

In this article, we review one of these documents on high voltage directed to the automotive market and see how it lines up with the existing aerospace standards.

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An Introduction to AS50881

For the last 17 years, Lectromec publications have discussed items related to the aerospace wiring installation standard AS50881. The standard is often referenced in many of our articles, but Lectromec has never really talked about what this standard is, why it should be used, who should use the standard, and what should be considered when the standard is employed.

To remedy this oversight, this article seeks to address the question many come to ask when approaching EWIS: why should I care about AS50881?

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EWIS and Aircraft Maintainability

The maintainability of the electrical wiring interconnection system (EWIS) is integral to the longevity of an aircraft. EWIS maintainability affects not only the EWIS itself, but any nearby system whose maintenance access is restricted by the location or function of the EWIS. Thus, high maintainability of the EWIS allows for faster, more efficient, and more precise maintenance of surrounding equipment and systems.

Original aircraft design must comply with EWIS regulations in the development stage to ensure long-term maintainability. It is important to know which regulations apply and which standards to follow when designing an aircraft to determine the appropriate maintenance requirements.

Here we will explore the requirements of some of the more common standards for EWIS maintainability in aircraft design.

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Light Weight and Normal Weight Wire Constructions

Saving weight is a large part of any aircraft design. Naturally, the electrical system is not exempt from the goal of shaving off a couple of pounds. This often comes in the form of looking for lighter connectors, lighter clamps, and also lighter wire constructions. Those that have done this have undoubtedly come across two classifications of wire construction: “Normal weight” and “light weight”. Of course, if the EWIS has to go on a diet, then the “light weight” construction looks like a good substitute for the “normal weight”… after all, why would the wire be called “light weight” if not for satisfying weight requirements. Read more

Latest Developments in Wire and Cable (Spring 2019)

Wire and cable standards are never proactive, but reactive to industry needs, and as the aviation world moves to high power systems, wire and cable must catch up to ensure the products are available for long reliable service life. Twice a year the SAE wire/cable community comes together to slowly push the standards and industry guidance forward; this year, New Orleans was the setting.

During this three-day meeting, several topics were discussed impacting the next generation of aircraft designs. Here, we cover a couple of these developments.

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Where EWIS Stops

Having well-defined and recognized system boundaries is the best means to ensure an analysis of that system is robust and does not leave any analysis gaps. Without an established limit and assigned responsibilities, arguments will ensue as to who is the responsible party and time/effort will be wasted with duplicated analysis.

Because an aircraft’s wiring touches nearly all of the systems, it can be confusing to understand where the system starts and stops, and this has led to confusion as to the responsible party for the wiring system design and/or maintenance. Some organizations have seen the responsibility fall on the electrical power systems teams, others, avionics. Regardless of who takes up the responsibility, a clear definition of the wiring system’s physical and logical boundaries must be agreed upon. Thankfully, there are several industry documents that can be relied upon.

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Maximum Harness Ampacity

The fundamental concept here is harness ampacity: the maximum amount of current transferred down a wire harness without exceeding the temperature rating for any component. Read more

Circuit Protection Selection Guidance

Circuit protection devices have existed since 1864; one would think that selection of circuit protection would be a straight forward task. However, it is not. NASA developed a seven-step process for circuit protection selection and both EN3179 and AS50881 provide some guidance. In a past article, Lectromec began to consider the differences between two major […] Read more

What is an EWIS Qualified Wire?

This is a question that Lectromec regularly receives. The reason for this question is that a parts-supplier or system-integrator is looking to find wires in compliance with EWIS requirements. Since there are so many ways to evaluate any component, the important question to consider is if a defined requirements list for aerospace wire exists? Here, […] Read more

AS50881 and EN3197 Harmonization

Working from a common knowledge base is critical for part interoperability. Take a standard screw; to install it requires a screwdriver (Phillips or Flathead), lining the screw up with the hole, and rotating clockwise to drive the screw. The screw works the same in Europe as it does in America, though the measurements might be […] Read more