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The formulae to calculate the loss factor for sheath $\lambda_1$ use the resistance of the sheath $R_{sh}$ at its maximum operating temperature. Because the temperature of the sheath is a function of the current, $I_c$, an iterative method is used for the calculation.
With crossing heat sources, a temperature rise of $\Delta\theta_{0x}$ applies at the hottest point.
| $\theta_{c}-T_{1} \left(W_{c}+\frac{W_{d}}{2}\right)$ | without screen |
| $\theta_{sc}-T_{scs} \left(W_{c} \left(1+\lambda_{11,sc}\right)+\frac{W_{d}}{2}\right)$ | with screen |
| $\theta_{sc}-n_{c} \left(T_{scs}+T_{f}\right) \left(W_{c} \left(1+\lambda_{11,sc}\right)+\frac{W_{d}}{2}\right)$ | multicore type with screen SC |