t = k²S² / I². This is the adiabatic equation rearranged. The k values are the usual ones for a conductor in a cable and not bunched. Confirm k in BS 7671 Tables 54.2 to 54.4.
The device still has to disconnect within the time required for shock protection. A conductor that can survive 2 seconds does not make a 0.4 second circuit acceptable if the device is slower than that.
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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