Calculate permissible current-carrying capacity Iz per IEC 60364-5-52 methodology: installation methods A1-E, ambient temperature and grouping correction.
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Current-carrying capacity: don't forget grouping and temperature
Standard table values apply to the ideal case: a single cable at 30 °C ambient. In practice, several circuits often run bundled in one trunking, and a loft reaches 45 °C in summer. The permissible capacity then becomes Iz = Iz,base × f_temperature × f_grouping – and can end up drastically below the table value.
Worked example: the classic planning mistake
A 3×1.5 mm² cable in conduit on a wall (method B2) carries 15 A per table. With 5 circuits bundled in the same trunking (factor 0.6) at 35 °C (factor 0.94): 15 × 0.94 × 0.6 = 8.5 A. A B16 breaker is clearly not permissible – only a B6 would be. The remedy: install 2.5 mm² or separate the bundle.
Installation methods
A1/A2: in conduit in a thermally insulated wall (worst heat dissipation) · B1/B2: in conduit/trunking on a wall · C: clipped direct · E: free in air or on cable tray (best cooling). Between A1 and E lies roughly 35 % difference in capacity for the same cross-section.
FAQ
Does grouping apply to short bundled runs? Bundled runs up to 1 m may be disregarded if the cables separate afterwards.
What about buried cables? Burial (method D) has its own tables including soil thermal resistance – deliberately not covered here.
