The equivalent thermal current $\underline{I}{th}$ is calculated by scaling the short-circuit currents $\underline{I}''{k}$ using correction factors $m$ and $n$. These factors represent the DC and AC components of the thermal load respectively. The calculation follows the matrix operation:
$$\begin{bmatrix} \underline{I}{th, 1} \ \vdots \ \underline{I}{th, n} \ \end{bmatrix} = \begin{bmatrix} \sqrt{m_1 + n_1} \ \vdots \ \sqrt{m_n + n_n} \ \end{bmatrix} \begin{bmatrix} \underline{I}''{k, 1} \ \vdots \ \underline{I}''{k, n} \ \end{bmatrix}$$
This allows for the determination of the thermal impact of short-circuit currents based on their AC and DC characteristics.