How to Calculate the Temperature Rise in Copper Windings From Resistance Measurements
Nearly all electrical conductors show a change in resistance with a change in temperature. A rise in temperature increases the amount of molecular agitation in a conductor hindering the movement of charge through the same conductor. To an observer, the measured resistance of the conductor has increased with the temperature change. This implies that meaningful comparisons of resistance for conductors of various sizes or materials must be performed at the same temperature.
Experimentation has shown that for each degree of temperature change above or below 20 degree C, the resistance of a pure conductor changes as a percent of what it was at 20 degree C. This percentage change is a characteristic of the material and is known as the ‘temperature coefficient of resistance’. For copper at 20 degree C the coefficient is given as 0.00393; that is, each change of one degree in the temperature of a copper wire results in a resistance change equal to 0.393 of one percent of its value at 20 deg C. For narrow temperature ranges, this relationship is approximately linear and can be expressed as:
R2 = R [1 + a(t2 – t1)]
Where:
R2 = resistance at temperature t2
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