Method and apparatus for detecting a temperature increase in an electrical insulator

The present invention provides a heat-sensitive warning device and a related method for visually detecting an increase in the temperature of the outer surface of an electrical insulator, which may indicate the unsafe flow of leakage electrical current through the electrical insulator, prior to a fire, an explosion or some other unsafe event. When the temperature of the outer surface of the electrical insulator increases to a preselected temperature, a visual indication of this rise in temperature will be provided by the ejection of a spool from a heat-sensitive warning device which has been attached to the outside of the electrical insulator. The temperature at which this visual indication of electrical insulator temperature increase occurs is preferably well below an unsafe temperature for the particular electrical insulator being used under the particular conditions of use, such as the autoignition temperature of coal or coal dust, so that the electrical insulator may be replaced prior to reaching this unsafe temperature.