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By: Michael Traskos

Non-Standard Standard Part Performance

Standardized products made by different manufacturers through different processes will undoubtedly healed variable product performance. The expectation is each ‘qualified’ product should perform comparatively well; anecdotal evidence suggests that this is not the case. This paper reviews recent work performed by Lectromec investigating the qualified wire/cable performance variability in both qualification tests as well as […] Read more

SAE Wire and Cable Committee Meeting Update – Fall 2019

The SAE wire and cable committee held their fall 2019 meeting in San Diego this year. As with every committee meeting, a lot of technical areas were discussed, progress was made, and some new ideas/problems are emerged. As we do after all these meetings, we put together a highlight of some of the talking points from the meeting.

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Determining Voltage Drop

If voltage is applied to a circuit and the attached equipment does not turn on, then there is an issue with either the circuit or the applied voltage (assuming the device is fully functioning). Sometimes glossed over in circuit design, the length and gauge of a wire can impact the voltage to the load; this is known as “voltage drop”. Just as the current carrying capacity of a wire/wire harness is impacted by the system and environment, so too is the voltage drop.

In this article, we go over the idea of voltage drop, guidance on its application in design, and an example of quantifying the voltage drop on a wire/cable.

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Wire Diagnostic Equipment

Finding wire faults/damage is not an easy task; now consider that problem across an entire aircraft. In-situ testing of wires/cables has always been viewed as something of a challenge to the industry. Given the branching that most harnesses undergo, the various wire lengths, splices, and numerous termination conditions, it can be difficult. Attempts to automate some of the testing has come to the development of Automatic Wire Test Sets (AWTS [pronounced “Eh-Wits”]).

Because there are so many ways to test a wire harness, the US military sought to create a performance standard to cover the general ideas and best practices of this equipment. Here, we review the standard and some of the performance features that can be expected when using equipment in compliance with the standard

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Checking a Coaxial Cable for Damage with a Multimeter – Part II

In the last article, Lectromec introduced a damaged coaxial cable and tried three techniques to distinguish it from an undamaged cable. The standard multimeter tests (capacitance, inductance, and resistance measurements) found no appreciable difference.

The idea of this evaluation was to demonstrate that the classic multimeter, while a great tool, is not suitable for detecting damage to coaxial cables.

But we cannot run an article and leave it without a solution. In this article, we continue the testing of a damaged coax cable to see what technology, if any, can identify and perhaps locate the damaged section of cable.

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Checking a Coaxial Cable for Damage with a Multimeter

The electronic multimeter is a great tool; invented in the 1920s, the multimeter has been used by millions of technicians and engineers seeking to measure circuits and troubleshoot electrical issues. So common are these tools now that it is almost impossible to consider a toolbox complete without one. 

While these are great tools and can be employed in a million situations, they are not the magic tool that can diagnose every circuit. If only one thing is remembered from this article: multimeters are not the tool to use for coaxial cables

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EWIS Physical Hazard Assessment

Aircraft system safety assessments are not a new concept. These safety assessments have a defined process for evaluating an aircraft which involve identifying its failure modes, top-level events, and eventual means to achieve an unsafe condition. Documents such as the SAE ARP4761 provide guidelines and methods for conducting the safety assessment process on civil airborne systems and equipment.

To follow the typical development cycle, the aircraft failure hazard assessment (FHA) is followed by the system failure hazard assessment and performed in parallel with the preliminary system safety assessments (PSSAs). This then evolves into the system safety assessments (SSA) and common cause analyses (CCAs). For those with a systems reliability background, this should all be second nature. For the rest of the community, these are often terms that we come across because of our work in this field.

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Wires and Fuel Compatibility

Whether by design or by accident, some wires in an aircraft will be exposed to jet fuel. Because of this, it is necessary to be prepared and select wires/cable types that will not suffer adverse effects of the exposure. Considering the impact of fuel on wiring is not idle musing about wiring systems; to quote the FAA AC120-97A, “Since 1959, there have been 18 fuel tank explosions on transport category airplanes”. Read more

Consequences of EWIS Implementation

In June 2019, Lectromec was asked to present at the USAF Mechanical Equipment and Subsystems Integrity Program (MESCIP) conference. With the electrical wiring interconnect system (EWIS) working its way into fleet sustainment activities, fleets now must take and apply the EWIS lessons learned.

Since the commercial segment has been subject to the 25.17XX EWIS regulations for more than a decade, the presentation examined the intended and unintended consequences of these regulations. For those seeking to integrate EWIS concepts into their fleet maintenance practices, this presentation gives an overview of the factors to be considered for your fleet.

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The Potential 270VDC EWIS Component Failure Impact

The More Electric Aircraft (MEA) design concept has placed, and will continue to place, a greater importance on aircraft electrical power and the supporting Electrical Wiring Interconnection System (EWIS) to accomplish flight critical tasks. To take the greatest advantage of weight savings from using electrically powered components, higher voltages have been brought into the aircraft power architecture.

The goal of Lectromec’s research was to generate data of the potential impact of EWIS component failure. Even with high voltage systems having been fielded for a couple decades, much of the published research provides information on the failure of 115VAC and 28VDC power systems. This research performed by Lectromec sought to fill in that gap.

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