The primary goal of an Earth grounding system is to maintain a low resistance between the Earth grounding electrode(s) and the surrounding soil and is represented by the base layer of the Protection Pyramid. As the ground resistance is reduced, a higher level of lightning immunity results.
Although the National Electrical Code Article 250.52 requires the resistance value between the Earth and the grounding electrodes to not exceed 25 ohms to maintain ground system safety and integrity, lowering ground resistance values as close to 1 ohm as possible further enhances the facilities protection against lightning related damage. A cellular tower provider typically seeks to achieve less than 5 ohms of ground resistance.
There are numerous variables to consider during the design and implementation of a grounding system; many having nothing to do with the actual grounding components. Factors to evaluate are the physical and chemical properties of the soil, soil moisture and oxygen content, along with climatic temperature and seasonal weather variations that alter soil resistivity. If a communication site does not have a comprehensive grounding system drawing in place when planning for expansion, then simply augmenting the existing grounding system for added growth may be inadequate. An undisciplined approach increases risk factors upon the entire facility and staff.
A properly installed grounding system may ultimately consist of an elaborate array of grounding electrodes, soil enhancement materials, and complex installation and bonding techniques. A compromised or corrupted ground system or component not only poses a serious threat to human safety, but also prevents any ground referencing SPD or lightning protection equipment from performing to its full capacity.