Soil Thermal Resistivity Derating Factors

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Following values are valid for the standards IEC 60364-5-52 and BS 7671. Derating factors for installing cables in soil with thermal resistivity other than 2.5 K·m/W.

Soil Thermal Resistivity (K·m/W) Soil Thermal Resistivity Derating Factor
Buried Direct Buried in Conduit
0.5 1.88 1.28
0.7 1.62 1.2
1 1.5 1.18
1.5 1.28 1.1
2 1.12 1.05
2.5 1 1
3 0.9 0.96

Tableau 52M - Facteurs de correction pour les câbles enterrés en fonction de la résistivité thermique du sol

Following values are only for the NF C 15-100. Derating factors for installing cables in soil with thermal resistivity other than 1 K·m/W.

Soil Thermal Resistivity K.m/W Derating factors
0.40 1.22
0.50 1.17
0.70 1.12
0.85 1.06
1.00 1
1.20 0.94
1.50 0.87
2.00 0.79
2.50 0.71
3.00 0.61

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