In order to calculate the start-up current of the heating cable, you must adjust conductor resistance value according to environment temperature; specific cable resistance is proportional to temperature gap,as shown in the following relationship:
Rt = R20 · [ 1 + α ( t - 20 ) ]
where:
- Rt = resistance at t temperature
- R20 = resistance at 20 °C temperature
- t = operating temperature
- α = temperature coefficient
α and [1 + α(t - 20)] values are reported on the tables below:
Conductor Type | Resistivity at 20 °C | α coefficient |
Copper (C) | 1.72 μΩcm2/cm | 0,004 |
Kumanal (K) | 41.0 μΩcm2/cm | 0 |
Nickel/Chrome 80/20 (T) | 113 μΩcm2/cm | variable |
Copper (C)
Temperature °C | 20 | 40 | 60 | 80 | 100 | 150 | 250 |
[1 + α(t - 20)] | 1 | 1.08 | 1.16 | 1.24 | 1.32 | 1.52 | 1.92 |
Kumanal (K)
Temperature °C | from 20 to 350 °C |
[1 + α(t - 20)] | 1 |
Nickel/Chrome 80/20 (T)
Temperature °C | 20 | 200 | 200 | 400 | 600 | 800 |
[1 + α(t - 20)] | 1 | 1.019 | 1.035 | 1.063 | 1.066 | 1.062 |
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