: For air or ground. Formula (simplified for copper, XLPE): [ k_temp = \sqrt\fracT_c - T_aT_c - T_ref ] Example: ( T_c = 90^\circ C ), ( T_ref = 30^\circ C ), ( T_a = 50^\circ C ): [ k = \sqrt\frac90 - 5090 - 30 = \sqrt\frac4060 = 0.816 ]
: Standard is 2.5 K·m/W (dry sand can be > 3.0, wet clay ~1.0). For actual ( \rho_soil ), correction tables apply. how to calculate cable size
