You can install the grounding conductor to the nearest accessible location on the following:
The building or structure grounding electrode system.
The grounded interior metal water piping system.
The power service accessible means external to enclosures.
The metallic power service raceway.
The service equipment enclosure.
Bonding of Electrodes
A bonding jumper not smaller than No.6 copper or equivalent shall be connected between the radio and television equipment grounding electrode and the power grounding electrode system at the building or structure served where separate electrodes are used.
The grounding electrode conductor or the grounding electrode conductor metal enclosures.
Antenna masts must be grounded to the same grounding electrode used for the electrical system of the building. This is necessary to ensure that all exposed, non-current carrying metal parts are at the same potential. In many cases, masts are incorrectly connected to the conveniently located vent pipers, metal gutters, and downspouts. This could create potential differences between lead-in conductors and various metal parts located in or on buildings, resulting in possible shock and fire hazards.