This "NORM" applies to solid core support insulators of types VKSt and VKS, which are used in overhead electrical lines with voltage ranges of 20 kV and 30 kV. The two types differ essentially in the minimum values of the bending breaking load.
ONORM E 4102-1989 history
1989ONORM E 4102-1989 Electrical overhead-lines; solid core line post insulators VKSt and VKS