The starting figure is a smooth curve, about 10.5 × (size ^ 0.56), then reduced for aluminium, raised only a little for 90°C insulation or surface wiring, and reduced again for grouping and ambient temperature above 30°C. It is aimed below ordinary clipped-direct ratings.
This is a cautious screen, not a copy of the BS 7671 or On-Site Guide tables. The numbers are rounded so a pass sits inside a margin. If the result is close, or if it fails, check the current tables before you decide. Do not put this figure on a certificate in place of the published value. A pass means the load is under this low figure. It does not mean the cable is selected. Current-carrying capacity, reference method and rating factors belong in BS 7671 Appendix 4.
These tools are quick guides for a ballpark figure. They are not certified design or test software, and a result on this page is not a design, a certificate, or a substitute for the current edition of BS 7671. Check the working and cross-reference it before you apply it to a real installation. Thanet Electrical Ltd does not accept liability for loss or cost arising from reliance on these figures, except where the law does not allow that liability to be excluded, including death or personal injury caused by negligence.
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