I am working on a project in which customer has provided me the data of different cables (2 core, 3 core, three and a half core, 4 core etc.) For cables where all cores have a same cross-sectional area, the inductance is calculated by a general formula mentioned in all textbooks, but I cannot find a way to calculate inductance in which cross-sectional area of neutral is different.
Is there any reading material about this particular topic?