Relative Thermal End Point Time and Temperature Index

The chemical composition of a wire’s insulation degrades at elevated temperature; this test provides data to establish curves describing the rate of degradation with respect to the exposure temperature. Samples are divided into four groups; each group is exposed to a selected temperature for defined time intervals. The time intervals are determined by an estimate […] Read more

A New Revision of MIL-HDBK-522

October 20, 2021 Laura Wishart

A new version (Revision C) of MIL-HDBK-522 was released on May 11, 2021. This article examines many of the changes made between Revision B and Revision C. Read more

Environmental Stress Crack

Environmental stress crack tests a sample ethylene plastic’s susceptibility to cracking as a result of environmental stress and the presence of selected chemicals (soaps, oils, detergents, etc.). Pre-damaged samples are mounted into the test fixture and submerged in a selected reagent (may depend on standard/ application) at a specified temperature. Specimens are inspected for evidence […] Read more

In Consideration of Backshells

September 1, 2021 Michael Traskos

The backshell of a connector is an item that perhaps does not get the attention that it should. Often the discussion of EWIS focuses on the wiring, the connectors, or managing the risk of EWIS failures, but the connector backshell is ignored. The simple connector backshell (that is anything but simple) is designed for support and protection of wires and cables physically and, in the case of signal cables, support and protect electrically too. The following is a brief introduction to backshells, their use, associated standards, and research that has been performed to determine what to look for when performing maintenance.

Addressing the Big Questions of Partial Discharge

June 11, 2021 Michael Traskos

In this high-voltage present, wires and cables must address new challenges, perhaps the most notable is partial discharge (also referred to as corona). This article discusses the fundamentals of partial discharge, its impacts on wiring design, and test methods used to assess a component’s partial discharge performance. The PD may occur between (1) the conductor and insulation, (2) within void in the insulation, (3) between insulation layers, or (4) between the insulation surface and shield. Read more

Tinning Test

The tinning test evaluates the ability of the tin layer over a copper conductor to protect the inner conductor from chemical degradation. Test samples are exposed to the following solutions: Hydrochloric-acid solution Sodium-polysulfide solution After a series of immersion cycles, as identified in the testing standard, each of the samples are visually examined for any […] Read more

Detailed Discussion of MIL-STD-1353 (Part 1): Tin Plating

April 21, 2021 Laura Wishart

The mating of the electrical wiring interconnect system (EWIS) is a non-trivial task. Between the functional requirements (the correct number of pins, sizing of contacts, etc.), there are also the performance requirements (operational environment, corrosion resistance, impedance matching, etc.). This is then further complicated by installation requirements (sizing), maintenance requirements (mating/demating cycles), and regulatory requirements (limitations of materials that can be used). Obviously, adding a connector to a wire harness is not a five-second activity. This article looks at the MIL-STD-1353 specific requirements for tin usage in aircraft connectors. Read more

Phase Delay

Phase delay is a measure of the delay in time a signal is emitted and when it is received at the other end. It is important that signal carrying cable adhere to a minimum phase delay to ensure timely and accurate function of the relevant system(s). The phase delay (propagation delay) is calculated from the […] Read more

A Summary of MIL-STD-1353, A Guide to Connector Selection

March 26, 2021 Laura Wishart

Due to the diversity of connector applications, each connector is liable to be subject to entirely different electrical stress, mechanical stress, environmental conditions, etc. Knowing the severity of conditions a connector will be exposed to during its service life is imperative during the selection process. The MIL-STD-1353 (Electrical Connectors, Plug-in Sockets and Associated Hardware, Selection and Use of) document aims to provide guidance in the selection of connectors used in equipment intended for military use. The document references several standards/ requirements that must be met for military equipment qualification and combines them into one easy-to-reference guide. Read more

Electric Aircraft Design Considerations

March 18, 2021 Michael Traskos

Electrical energy storage has reached a point where it is possible for the manned vehicle propulsion to use non-petroleum based energy. To achieve this goal, it has required a lot of research, design, and innovation that has pushed these vehicles to depend on high voltage electrical power systems and forego the use of hydraulics and pneumatics. If electrical aircraft are the aircraft of the future, what are the design factors that the EWIS community will have to address? Read more

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