Service entrance cables have special mounting requirements. You must support them within 12 in. of every service head, gooseneck, or connection to a raceway (or enclosure) [230.51(A)] in that run. The maximum interval between supports for a service entrance cable is 30 in.
What exactly is a gooseneck? It’s a loop-down in the cable, put there to prevent water from running along the cable and entering the service entrance. The shape it takes on resembles the neck of a goose, thus