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Test method

The samples of the insulation or sheath material are prepared in small strips to a mass of 50 ± 5 mg. The samples are then placed in a glass tube with a strip of litmus indicator paper, and the tube is then placed in thermostatic equipment at the specified temperature.

The time that elapses for the litmus paper to change from pH 5 to a value between pH 2 and pH 3 is measured, which is in the colour variation to red. If the colour of the paper does not change, the test continues for the duration established in the specific cable standard.

The test is considered to have a satisfactory outcome if the mean value of the thermal stability times is not less than the value specified in the specific cable standard.