Cable Installation Method

The way a cable is installed fundamentally affects how efficiently it can dissipate the heat generated by current flow. Reference Method A (enclosed in thermally insulating wall) provides the worst cooling and lowest ampacity. Reference Method B (enclosed in conduit on a wall) is slightly better. Reference Method C (clipped direct to a surface) allows reasonable convective cooling. Reference Methods E and F (on perforated cable tray, single-layer and multi-layer respectively) provide good ventilation. Reference Method D (buried direct in ground) relies on soil conduction. Each reference method has its own column in the ampacity tables, and the same 10mm² cable might be rated at 57A in conduit (Method B) but 76A clipped direct (Method C) and 88A on open tray (Method E). Engineers must accurately identify the installation method for each section of a cable route — and where a cable passes through different conditions, the worst section determines the rating for the entire cable. Some routes combine methods: a cable might leave a distribution board through conduit (Method B), run along a tray (Method E), then pass through a wall with thermal insulation (Method A). The ampacity for such a route is determined by the most restrictive method.