Conductor cable must interconnect all air terminals (points) and shall form a two-way path from each air terminal horizontally or downward to connection with grounding rods.

Exceptions to the above rule are:

1. When the conductor cable drops from a higher to lower level providing the lower roof conductor horizontal run does not exceed 40 feet,
2. Air terminals may be dead ended with only one path to a main conductor on roofs below the main protected roof provided the conductor maintains a horizontal or downward run and is not more than 16 feet long.

Conductor cable shall maintain a horizontal or downward course, free from any "V" or "U" pockets, when a "V" or "U" pocket is necessary, a down connector must be provided from the base of the pocket to a convenient main conductor on a horizontal or downward path.

A conductor cable must not be through the air unsupported for a distance of more than 3 feet. Ridge conductors shall be coursed along ridges of gable, gamble and hip roofs and around the perimeter of flat and gently sloping roofs.  Conductor cable must be coursed through or around obstructions such as ventilators, chimneys, cupolas and the like. in a horiziontal plane with the main conductor.

Down conductors shall be as widely separated as possible and located at the perimeter of a roof structure.  Their location will depend upon location of air terminals, the most direct coursing of cable, the location of utilities, metallic piping and etc.

There shall be a minimum of two down conductors on any kind of structure. Structures with a perimeter exceeding 250 feet shall have a down conductor for every 100 feet of perimeter.

a main sized conductor cable shall be used to interconnect electric service, antenna grounds, metallic water piping, telephone systems and other large grounded metallic masses.

Each down conductor must terminate in a copper-clad ground rod or grounding plate. In sand or gravel soil, at each grounding location, two or more ground terminals at least 10 feet apart shall be driven vertically to a minimum depth of 10 feet,  If bed rock is near the surface, copper conductor cable shall be laid in a minimum trench length of 12 feet and 2 feet deep extending away from the building at each down conductor.

Chimneys, metal vents and cupolas must be provided with roof points so that no outside corners in more than 12 feet from a roof point.

Electric, telephone and antenna system grounds, metal well casings within 25 feet of the protected building and underground metallic piping shall be bonded together and to the lightning protection system.  Such piping included gas piping, water service, underground conduits and etc.  If electrical, telephone or other systems are grounded to a metallic water pipe, only one bonding connection to the water pipe system is required, provided that the pipe is electrically continuous between all systems. If it is not, the nonconductive sections shall be bridged with conductor cable or the bonding connections shall be made at a point where electrical continuity is assured.

Main sized conductors and connectors shall be used for such ground connections.  Metal bodies of inductance that are within 6 feet of the main conductor or other bonded metal body shall be bonded to the system.  A metal body of inductance shall be bonded at the closest point to the lightning protection system.

The following sketches are provided for clarification of the above information.

Phone: (210) 832-9500     Fax: (210) 568-1982