1. Requirements relating to heating are based on an ambient air temperature of 25.C [17.F). A temperature test may be conducted at any ambient air temperature and the variation from 25.C is added to or subtracted from the observed temperature reading.
    

2. Other than in those cases where it is specifically stated that temperature determinations are to be made by the change-of-resistance method, temperatures are to be measured by means of thermocouples. A thermocouple-measured temperature is to be considered constant if three successive readings, taken at intervals of 10 percent of the previously elapsed duration of the test (but at not less than 5-minute intervals), indicate no change. The junction of the thermocouple is to be secured in contact with the point on the surface at which the temperature is to be measured. The thermocouple is to consist of wires not larger than No. 24 AWG (0.21 mm² ).
   
   Exception No.1: In here the thermocouple is used to measure temperatures of electrically live points, electrical insulation having a maximum thickness of O.028 inch (0.71 mm) may be located between the thermocouple and the live points.

          Exception No.2: The coil temperature is to be determined by the change-of-resistance method.

          Exception No.3: The ambient temperature may be determined by a thermometer.

3. When thermocouples are used in the determination of temperatures in connection with the heating of
   electrical devices, it is standard practice to use thermocouples consisting of No. 30AWG (0.05 mm²) iron and constantan wires and a potentiometer-type indicating instrument. Such equipment is to be used whenever referee temperature measurements are necessary. The thermocouple wire is to comply with the requirements for special thermocouples as specified in the table of limits of error of thermocouples in Temperature Measurement Thermocouples, ANSI MC96.1-1982.
    

4. The temperature rise of a copper or aluminum winding is to be determined by the change-of-resistance method using the following formula (windings are to be at room temperature at the start of the test):
   
                                     
   
   in which:
   
   t is the temperature rise,
   R is the resistance of the coil at the end of the test,
   r is the resistance of the coil at the beginning of the test,
   k is 234.5 for copper and 225.0 for aluminum,
   t₁ is the room temperature in degrees C at the beginning of the test, and
   t₂ is the room temperature in degrees C at the end of the test.