Acceptable grounds for protective grounding are as follows:
A vertical ground wire which has been tested, found safe, and is connected to a power system multigrounded neutral or the grounded neutral of a power secondary system where there are at least three services connected;
Guys which are bonded to the grounds specified in paragraphs (m)(4) (i) and (ii) of this section and which have continuity uninterrupted by an insulator; and
If all of the preceding grounds are not available, arrays of driven ground rods where the resultant resistance to ground will be low enough to eliminate danger to personnel or permit prompt operation of protective devices.
Communications cable sheath or shield and its supporting strand where the sheath or shield is:
Bonded to an underground or buried cable which is connected to a central office ground, or
Bonded to an underground metallic piping system, or
Bonded to a power system multigrounded neutral or grounded neutral of a power secondary system which has at least three services connected;