Thermal Index

The long-term thermal stability of wires and cables is important for reliable aircraft performance. Wires used at temperatures at or above the temperature rating can quickly degrade and create the need for premature rewiring of systems.

The thermal index test (also known as the Relative Thermal Life and Temperature Index) is based on multiple cycles of elevated temperature exposure, mechanical stressing, and electrical insulation integrity checks. The goal of this test is to determine the maximum continuous operational temperature for the wire/cable for a targeted time interval (the common goal for aerospace wires is to find the maximum continuous temperature for 10,000 hours of operation). This is achieved with long-term exposure to temperatures above this desired temperature rating.

The pass/fail criteria for this test are based on the individual wire/cable specifications. Often, the target is to use an Arrhenius plot to predict the wire/cable performance at the targeted temperature rating.

Parameters that can be changed with this test include:

• Number of samples
• Test temperatures
• Test duration
• Assessment techniques