For multiple cables twisted or bound together, a combined diameter circumscribing all cables can be calculated. The resulting value is also approximatively correct for three loose cables in touching trefoil formation.
The equivalent diameter over the conductors for three core cables without a filler (not round), can be calculated by dividing the circumference with $\pi$. In case of three-core cables, they are called triplex; and in case of two-core cables we call them duplex.
For multiple unequal round objects, possibly non-touching, finding the smallest circle that encompasses all other circles is not easy and we consider following approximation as presented in stackoverflow.com
| $F_{eq} D_e$ | multiple cables |
| $\frac{n_c D_{shj}+\left(D_{shj}+2\left(t_{ab}+t_{ar}+t_j+t_{jj}\right)\right) \pi}{\pi}$ | duplex/triplex cables |
| $F_x D_{core}$ | pipe-type cables |
| $f{\left(\right)}$ | air-filled pipe with objects |
