42.11 Coil and winding temperatures are to be measured by thermocouples located on exposed surfaces,except that the resistance method may be used for a coil that is inaccessible for mounting thermocouples,such as a coil:a) Immersed in sealing compound;b) Wrapped with thermal insulation; orc) Wrapped with more than two layers of material such as cotton, paper, or rayon more than1/32 inch (0.8 mm) thick.In an alternating-current motor, the thermocouple is to be mounted on the integrally-applied insulation ofthe coil wire.42.12 The temperature rise of a winding is determined by the resistance method by comparing theresistance of the winding at a temperature to be determined with the resistance at a known temperatureaccording to the formula: