Grundfos SP Series Installation And Operating Instructions Manual page 447

Example:
U = 3 x 380 V
I = 10 A
L = 120 m
U = 2 %
L 120

Lx = ------- - = --------- - = 60 m = q 6 mm
U
2 %
U = 3 x 380 V
I = 10 A
U = 2
%
L = 120 m
2
447