In a commercial building, the grounding electrode conductor or bonding conductor installed for a communications system is sized using Table 250.66.

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Sizing the grounding conductor depends on what that conductor is connecting and what it’s protecting. The table 250.66 is used to determine the minimum size of a grounding electrode conductor that bonds the building’s grounding electrode system to the electrical service equipment (or to feeders), based on the size of the overcurrent protection for the service or feeder. It is specifically tied to the service/feeder grounding to the earth.

For a communications system, the grounding/bonding conductors follow different rules found in Article 800 (and related sections) and are sized using the equipment grounding conductor sizing rules (such as table 250.122) or bonding sizes specified there, not table 250.66. Therefore, the grounding electrode conductor or bonding conductor for a communications system is not sized using table 250.66.