Pull Through Testing- An Addition to NEMA 27500

August 18, 2021 Michael Traskos

An area that has been poorly defined until recently has been the potential damage to wire/cable insulation due to wiring installation on aircraft. The latest revision of NEMA 27500 has looked to address this gap in cable assessments. In this article, we review the test requirement, expected performance, and what the results may mean to designers and installers.

Partial Discharge at Altitude

July 27, 2021 Laura Wishart

PD is not a simple phenomenon to model as there are many environmental factors that have influence. Factors such as heat, humidity, pressure, are some that can change the voltages required to initiate and extinguish PD within a wire/cable’s insulation. This article specifically discusses the influence of altitude on partial discharge events. The consideration of the operational altitude effect on partial discharge is particularly necessary for aerospace applications as aircraft tend to spend a lot of operating time at high altitudes.

Insulation Tensile Strength and Elongation of Insulation

This test provides tensile property data on extruded electrical wire insulation removed from the wire/cable specimen. Identifying the insulation’s tensile properties are useful to determine the ability to withstand mechanical stresses the wire/cable may experience in service conditions. Using a power driven tensile test machine, the insulation is stretched until breakage. At the end of […] Read more

Circumferential Elongation (PTFE only)

This test determines the elongation of insulation of a wire in a circumferential direction. This test was developed to measure the resistance of polytetrafluoroethylene (PTFE) insulation to rupture when under a radial stress. Using a power driven apparatus built by Lectromec technicians, a cone shall be driven through the insulation. At the end of the […] Read more

Accelerating Aging

The test determines if the insulation of a wire has been converted to a thermoset material by polymer crosslinking. The test is performed for a short time period at a temperature much greater than the temperature rating of the insulation. To pass this test, the wire must withstand the bend and wet dielectric tests after […] Read more

Elevated Temperature Aging

This test determines if the wire insulation can withstand a temperature aging test for a time period at a temperature greater than the insulation temperature rating. The wire must then withstand the bend and wet dielectric tests after the thermal exposure for the specimen to pass the test. This test is sometimes included as part […] Read more

Thermal Endurance

This test determines the ability of the insulation of a firezone or similar wire to resist degradation due to exposure to high temperature. Degradation is judged by change in conductor resistance, cracking during bending, insulation dielectric breakdown, or decreased resistance to fluids. All of these points shall be tested by using 3 foot long samples […] Read more

Wrinkle Test

This test is used to evaluate the quality of insulation and its ability to withstand wrinkling. Wrinkles can occur to insulation when bent back and forth frequently, eventually causing the insulation to deteriorate. The particular concern here is on tape wrapped insulations. During the fabrication process, an adhesive is used to hold the tape wrap […] Read more

Thermal Shock

Temperature cycling can cause rapid degradation of wire/cable insulation integrity. This can manifest and insulation splits, cracks, and/or delamination. Often an overlooked test method for assessment, the thermal shock test proves and excellent means of assessing the construction quality of a wire or cable. The test focuses on a single high-temperature to low-temperature exposure and […] Read more

Humidity Resistance

The humidity resistance test seeks to evaluate the impact of prolonged heat and humidity exposure to wire/cable insulation. This accelerated environmental test is meant to simulate the environmental conditions in Severe Wind and Moisture Prone (SWAMP) areas on aircraft to analyze the possible detrimental effects. A sample is considered to have failed if there has […] Read more