The part of the perimeter of the cable trough which is effective for heat dissipation. If the trough is shaded, then the perimeter is the whole inner surface. If the trough is exposed to solar radiation, then the top cover is not considered effective for heat transfer.

$p_{\mathrm{tr}}$

m

$2 h_{\mathrm{t}} + 2 w_{\mathrm{t}}$ | shaded troughs |

$2 h_{\mathrm{t}} + w_{\mathrm{t}}$ | unshaded troughs |

$w_{\mathrm{t}}$

Inner width [m]