Testing & Assessment

Thermal Life of Wires and Cables

April 22, 2019 Michael Traskos

While there is a wide range of products from which to choose, across many of these specifications there is a common element: maximum temperature rating. Here, we walk through a couple of the methods for assessing a wire/cable’s maximum temperature rating. At the end of this article, we delve into weaknesses of this assessment method and elements that should be considered when selecting a wire for your high temperature application. Read more

International Test Standards for Aircraft Wire Tests

January 15, 2019 Michael Traskos

Frequently, Lectromec’s articles have focused on wire and cable testing from US-focused standards such as the SAE and US military (MIL) documents. While these are standards frequently cited, there are other standards organizations that support the aerospace wiring community. Thankfully, many of the standards share a common base and, as is the case with many of the SAE standards, these have been harmonized with European standards. In this article, we will review some of the European wire/cable test standards, variation from similar test methods, and their availability in Lectromec’s lab. Read more

Use of MIL-T-81490 cable in place of a MIL-DTL-17 cable

December 20, 2018 Michael Traskos

A common ‘go-to’ cable for RF applications is the MIL-DTL-17 cable. Many of the MIL-DTL-17 cables are rated to 1 GHz, some to 12.4 GHz (like M17/128), and only a couple at 20GHz (e.g. M17/130 and M17/133 – a word of caution with the /130 and /133 constructions: these are unjacketed cables with an exposed external conductor/shield). There is the M17/205 construction that is spec’d for up to 50GHz, but that comes with a caveat: attenuation. The accompanying figure shows the attenuation per 100ft of M17/205 cable; while the attenuation does rise quickly with higher frequencies, the specification does not provide any attenuation limits beyond 10 GHz. Read more

Mechanical Performance of Cables at Low Temperatures

October 5, 2018 Michael Traskos

The environmental extremes under which wiring exists in aircraft can rapidly degrade materials that are not prepared or designed for those conditions. Without a doubt, high-temperature ranges that are typically considered for aircraft wiring eliminate most wire insulation types that are suitable for ground-based home applications. Lectromec has covered several types of high-temperature tests in past articles. But at low temperatures, what tests exist to help identify which wires are ideally or adequately suited for aerospace applications? One of the tests that investigates the performance of wires in cold conditions is known as the cold bend test. Read more

Should Polyimide Insulated Wire be Trusted?

September 25, 2018 Michael Traskos

The history of polyimide insulated wire is one that has numerous opinions and a lot of misconceptions. After several incidents involving polyimide wire on aircraft in both military and commercial, many within the aerospace industry refused to put any polyimide insulated wire/cable onto the aircraft they design/maintain. As is often the case with components involved in incidents, a lot of facts and myths get jumbled together. Read more

High Current Testing

August 14, 2018 Tristan Epp Schmidt

Several things can go wrong when a wire or cable is subjected to an electrical current exceeding its design limitation and none of them are good. These include, but are not limited to, melting of the insulation, smoking, insulation degradation, promotion of intermetallic growth between the plating and conductor, melting of the conductor, melting of the conductor plating, and conductor embrittlement. Thankfully, if the wire/cable is being used within its temperature and current ratings, the wire should experience very little of the above phenomena. Read more

DO-160, EWIS, and EMI

August 6, 2018 Michael Traskos

Designing a circuit diagram for a system comprised of Line Replaceable Units (LRUs) is usually a straightforward process: identify the inputs and outputs of the system and connect them with wires and cables. Taking that simple high-level circuit diagram and implementing the physical design into an application can be quite difficult. This requires the proper connectors, optimized the physical routing, and ensuring negligible impact from electromagnetic interference (EMI). From an implementation perspective, it cannot be understated how much EMI can impact system performance ranging from degraded performance to make a system completely inoperable. Thankfully, there are test methods to evaluate the susceptibility of electromagnetic interference of a wire harness design. Read more

Testing the Performance of AFCBs

July 16, 2018 Michael Traskos

Arc Fault Circuit Protection has been a technology that dates back to the 1990s. Despite this not being a new technology, the breath of its implementation is still limited. The device owes its inception to arcing events that occurred on in-service aircraft. Because of these events, the wiring community sought to create wiring that was arc track resistant, and the circuit protection community sought to cut off the arcing event before too much energy was released. This has been captured in the requirements of AS5692 for AC circuit protection, and AS6019 for DC protection Read more

Galvanic Corrosion and Red Plague

July 7, 2018 Devon Gonteski

Some have brushed the issue aside saying that they have never seen it, thus it is not a problem. To put the issue of red plague into perspective, a worst-case estimate suggests as much as 3% of braided silver-plated copper shields have some degree of red plague. Across the aerospace industry, this equates to millions of dollars each year in scraped products, rewiring, and maintenance actions. Read more

Unwanted Energy Storage in Cables – Dielectric Constant

June 22, 2018 Tristan Epp Schmidt

A good wire insulation is more than just preventing electrical energy from leaving the conductor; there are dozens of properties that are important to its performance and usability. One of these that is easy to overlook is the wire’s dielectric constant. Read more