T is the temperature of the winding

T is the temperature of the winding in degrees C;R is the resistance of the coil at the end of the test in ohms;r is the resistance of the coil at the beginning of the test in ohms;t is the room temperature in degrees C at the beginning of the test; andK is 234.5 for copper, 225.0 for electrical conductor grade (EC) aluminum; values of the constant for other conductors shall be determined.The winding shall be at room temperature at the start of the test.49.9 The values shown in Table 22 are the ultimate limits that shall be obtained during the temperature test. The test can be performed at any ambient temperature in the range of 10°C -40°C (50°F - 104°F).49.10 When a device is rated for an ambient temperature higher than 25°C (77°F), the rating shall be indicated in the instruction manual in accordance with 76.3 (n).49.11 Thermocouples shall consist of wires not larger than 24 AWG (0.21 mm?) and not smaller than 30 AWG (0.05 mm2). When thermocouples are used in determining temperatures in electrical equipment, it is common practice to employ a temperature-indicating instrument with thermocouples consisting of 30 AWG iron and constantan wire. Such equipment shall be used whenever referee temperaturemeasurements by thermocouples are required. The thermocouples and related instruments shall beaccurate and calibrated in accordance with good laboratory practice. The thermocouple wire shall conform with the requirements for special thermocouples as listed in the Tolerances on Initial Values of EMF versus Temperature tables in Annex A,Ref.No.60.49.12 A temperature shall be determined to be constant when three successive readings taken atintervals of 10 percent of the previously elapsed duration of the test, but not less than 15 minutes, indicate no continued rise.