This is the radius over all insulation layers up to the first metallic shielding layer.
For single-core cables, this is typically the radius of the insulation without the insulation screen (outer semi-conducting layer). In case of nulti-core cables screen, this is the radius from the center of the cable to the screen, sheath or armour.
| $\frac{D_{ins}}{2}$ | Single-core cables, with screen/sheath |
| $\frac{D_{ab}}{2}$ | Single-core cables, without screen/sheath, with armour |
| $\frac{D_j}{2}$ | Single-core cables, without screen/sheath, without armour |
| $\frac{D_{scb}}{2}$ | Multi-core cables, common screen (CC) |
| $\frac{D_{ins}}{2}$ | Multi-core cables, separate screen (SC/SS) |
| $\frac{D_{scs}}{2}$ | Multi-core cables, without screen, with sheath (SC/SS) |
| $\frac{D_f}{2}+t_{ab,1}$ | Multi-core cables, no screen, no sheath, with armour |
| $\frac{D_j}{2}$ | Multi-core cables, no screen, no sheath, without armour |
