AS50881 and Connectors

The fundamentals of wires themselves can be reduced to a simple math; the basic equation being that each wire possesses two ends and therefore two terminations. When factoring in the addition of cables, or shielding, the variables at hand can make the design of terminations vastly more complex. This increasing intricacy can dictate the reliability and safety of wire harnesses, which themselves hinge upon the precision of their terminations as they form the foundation of EWIS systems.

Amidst the vast amount of aerospace standards, AS50881 stands out as a comprehensive guide to requirements to ensure wire termination safety specifically in connector installation and design. In its annals, AS50881 outlines that connectors should be used whenever equipment must be regularly disconnected for maintenance or any other service activities. Connectors facilitate much more rapid mating and de-mating of components, minimizing the risk of errors during reinstallation.

Installation

Additionally, AS50881 states connectors should not be installed in such a way that they could provide any sort of mechanical support for personnel such as serving as foot or handholds; this in alignment with FAA requirements in 25.1721 (Protection of EWIS). This requirement drives design on where connectors can be placed, involving the consideration of human factors like how personnel might access equipment during maintenance operations. Some of these design principles require an experienced designer to understand factors impacting maintenance or are only made apparent after a prototype is created and some field experience is gained. Several years ago, Lectromec published an article on the impact of mechanical loads on wires and showcased how a weight placed at the center of a cable could impact its electrical resistance.

Delving into the intricacies of connector installation, AS50881 unveils a wealth of considerations packed into its paragraphs. For instance, the standard dictates that receptacles for pressurized connector systems must be installed with the flange on the high-pressure side; this is a practical measure to prevent air leakage and ensure sealing integrity. This requirement not only influences the fabrication of wire harnesses but also underscores the interconnectedness of design elements within the system. Moreover, the document mandates the avoidance of cadmium-plated connectors in contact with titanium or carbon fiber composite compounds due to concerns of galvanic corrosion (a restriction on cadmium plated connectors still exists to support aging platforms even though regulations limit the use of hazardous materials).

Separation Distance

Navigating deeper into AS50881, the standard identifies requirements on adequate connector-to-connector separation to facilitate easy mating and de-mating. This requirement, though seemingly straightforward, acknowledges the ergonomic considerations essential to efficient maintenance operations in small spaces. Those who have ever had to reach into an electrical cabinet to blindly mate or de-mate a connector can attest to knowing that having sufficient maneuvering space is much appreciated. The standard reveals that at least one inch must be provided around the coupling rings of circular connectors, and if possible, those of us with larger hands appreciate the additional space. AS50881 additionally mandates that if there is heavy congestion in the connector area where the one-inch separation is not possible, a minimum clearance of 0.75in should be provided.

Identification

The last area covered within this article is that of connector identification. The identification of any aircraft component is intended for several reasons:

1. Identification – it should not be difficult to identify critical information about any component.
2. Support original installation – the identification should, if possible, provide information to support proper installation and connection with the rest of the aircraft.
3. Maintenance – A maintainer, whether they are performing a general visual inspection of a zone, directly working on that system, or neighboring components, should be able to clearly identify the component.

Connectors do not escape these three identification requirements, and because of the complexity of EWIS, in fact, must show even more information.

The connectors should be identified to facilitate proper mating. Any areas where several of the same connectors are collocated should not only be keyed, but also have unique identification to assist with mating.

The AS50881 has a maximum distance requirement for connector/harness identification from the end of the connector. The obvious reason here is to support installation (the further the label is from the final connection point, the more error-prone the installation will be. AS50881 does provide some relief on this requirement for areas where it might not be visible, such as behind a rack.

As part of good design, these connector tags should be durable and have markings that will not fade or become FOD when subject to the operational conditions within the zone. Thankfully, there are many good options available to achieve this, but it is recommended that the material/marking compatibility be verified with any fluids that might be present in the zone.

Conclusion

As technology advances, the significance of connector safety extends beyond mere functionality to encompass factors like voltage rating, contact separation, and safety features. Lectromec’s insights into connector selection and failure analysis serve as invaluable resources in navigating these evolving complexities, ensuring the reliability and longevity of aerospace systems in the face of future challenges. Factors such as construction, plating, contact separation, partial discharge, and separation distance will drive high-voltage connector selection for the coming decades.

For additional information regarding aerospace connectors, feel free to explore these other Lectromec articles on connector selection, consideration of plating types, and a breakdown of the different factors impacting connector failure or contact Lectromec for further assistance.