Proper grounding is essential to the effective functioning of tree lightning protection systems. The procedure for grounding will depend upon the character of the soil and surrounding conditions
Please remember that the underground spread of the root system is usually equal in area to the spread of the branches above ground.
Extend standard conductor down trunk and out and away from base of tree in a shallow trench (approximately 6-8 inches in depth). This conductor shall terminate at a driven ground extending down to permanent moisture. A 1/2" x 10' Copper Clad Ground Rod, No. 138 and Bronze Ground Clamp, No. 50 provide effective grounding in normal soil conditions.
Fork Type Ground
The fork type ground system is often practical to use, due to soil conditions, nearness of trees to buildings, concrete sidewalks, property lines, etc. The standard down conductor is placed in a shallow trench and extended out from base of tree from 12 to 15 feet or even further. At end of this conductor a driven ground to permanent moisture is added. Standard conductors are attached to the main down conductor with No. 198 Fork Ground Connector and placed in shallow trenches forming a fork. Large trees require an additional ground.
Multiple Grounds
When it is impossible to drive ground rods to a distance of 10 feet, multiple grounds driven as deep as possible separated at least 6 feet apart are most effective (see illustration). Another alternative is copper ground plates buried in a shallow hole.
Ground Interconnections
If the grounding of building protected with a lightning protection system is within 25 feet of a tree, the two systems should be interconnected. If the lightning protection ground of the tree is within 25 feet of a water pipe, sprinkler system, or a deep well casing, a bond connection should be made between them.
Trees in Groups
The major trees in a group can be protected to give ample protection for the smaller ones. If there are several trees in a row (all major trees), the grounding may be made by "common grounding" by trenching from the base of each protected tree to the depth grounds(s), as long as these depth ground locations are not more than 80 feet apart. Depth grounds shall be added as required. This avoids the practice of making independent groundings for each tree, thus reducing the cost of the lightning protection.