The distances dpk and d’pk are measured from the centre of the p th cable to the centre of cable k, and to the centre of the reflection of cable k in the ground-air surface respectively (see figure 1).The value of ∆θ in the equation for the rated current in 1.4 of part 1 is then reduced by the amount ∆θ p and the rating of the p th cable is determined using a value T 4 corresponding to an isolated cable at position p.This calculation is performed for all cables in the group and is repeated where necessary to avoid the possibility of overheating any cable.