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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