Lightning is created when a path of least resistance is established between an upward streamer and downward leaders. Properly designed grounding systems work on a similar principle by creating a path of least resistance in commercial and residential structures that channel excessive voltages away from buildings, equipment and people.
Lightning protection grounding systems in commercial and residential structures dissipate the electrical current from lightning that travels through the downconductors after the strike was captured by a lightning arrester such as a lightning rod or other type of air terminal. But grounding systems can also disperse electrical surges caused by power-switching transients.
Because lightning grounding systems for commercial and residential structures are buried underground and subjected to extreme environmental conditions, it’s important to consider the reliability of the materials used. (Companies like Erico and Harger manufacture high-quality components using copper or copper-covered steel).
A grounding system typically comprises five parts:
- A grounding electrode conductor, the first in a system of conductors that ensures electrical contact with the earth or, if that is not possible, another suitable inductive body.
- The grounding connections, which connect the grounding conductors to the ground electrodes.
- The grounding electrodes, more commonly known as the ground rods. When buried into the earth, ground rods work by dissipating electrical current into the surrounding soil. This occurs in concentric, progressive waves called the sphere of influence. For lightning protection, ground rods are usually laid out in single (starburst) or multiple (crow’s feet) radial arrays, but many other design patterns exist.
- The electrode to soil resistance. Soil resistivity, which is the opposition to electrical current flow measured in Ohms, depends on the type of soil (clay, rock, loam, etc.); moisture content; mineral content; typical climate/seasonal variations; and the presence of contaminants.
- The soil. By measuring soil resistivity at different depths, Lightning Elimination Systems can determine the optimal implementation of ground rods and select the most conductive soil for their installation.
Like the connections between air terminals, downconductors and grounding systems, the
components within a grounding system must be properly bonded. Any existing conductive equipment on-site – chassis, piping or anything metallic – must also be bonded to the grounding system to prevent hazardous voltages in the event of a lighting strike or power-switching transient.