Single-phase Ib = P / (V × power factor). Three-phase Ib = P / (√3 × V × power factor). Use 1 for a resistive load such as a heater.
This is the load current, not the cable rating. Diversity, inrush and the rating factors in Appendix 4 come after Ib.
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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