In order to calculate the resistance ( Rt ) of a cable with a copper conductor at a fixed temperature ( t °C ) , the value of correction at 20 °C must be multiplied by a reduction factor which can be obtained from the table below .
Temperature °C
Factor
20
1.000
21
1.004
22
1.008
23
1.012
24
1.016
25
1.020
30
1.039
35
1.059
40
1.079
45
1.098
50
1.118
55
1.138
60
1.157
65
1.177
70
1.196
75
1.216
80
1.236
85
1.225
90
1.275
The correction faction are calaulated with the formula: