In = √(Ia² + Ib² + Ic² − IaIb − IbIc − IcIa). Equal line currents give about zero neutral current. A single loaded phase returns all of that current on the neutral.
This assumes each current is in step with its own phase voltage. Electronic loads can add triplen harmonics, and those add in the neutral. Tick the box to lift the result by half as a rough allowance. It is not a harmonic survey.
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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