1 Scope
The method described in this International Standard is applicable to any type of cable
and group running horizontally, provided that the cables are of equal diameter and
emit equal losses.
Information is provided on the reduction in permissible current when cables are mounted
adjacent to each other. It is limited to the following cases:
-
a) a maximum of nine cables in a square formation, see Figure 1, and
-
b) a maximum of six circuits each comprised of three cables mounted in trefoil, with
up to three circuits placed side by side or two circuits placed one above the other,
see Figure 2.
Caution is advised where air flow around the cables may be restricted by proximity
to neighbouring objects.
NOTE Further work is to be done to extend and refine the data and to include the effect
of dielectric loss.
Information is provided for the following situations:
-
— Where a rating for one cable or circuit assumed to be isolated exists, group reduction
factors can be derived for the same type of cable, see 4.1.
-
— Where previously calculated ratings are not available, the data provided can be used
to calculate permissible currents for groups of cables, using the formulae in parts 1 and
2, see 4.2.
-
— Where adequate clearances can be provided between cables to avoid a reduction in permissible
current, see clause 5.