GB/T 11026.8 - 2014 is the eighth part of the series of standards for the heat resistance of electrical insulating materials. It introduces the method of determining the heat resistance index (TI and RTE) of insulating materials with a fixed time limit method. The standard specifies the test conditions, sample preparation, and test process. For example, the sample is tested for a fixed time at a specific temperature to observe its performance changes. Through this method, the heat resistance of insulating materials at different temperatures can be accurately evaluated, providing important data support for the selection of insulating materials for electrical equipment and ensuring the long-term stable operation of equipment.