The length and diameter of the ground rod not only affe […]
The length and diameter of the ground rod not only affect its resistance but also its driving characteristics. Although larger diameter ground rods do not have an appreciably lower ground resistance value, they do have a larger steel core that makes them easier to drive in harder soil by providing extra rigidity.
It's probably no coincidence that most rods driven in Canada, with its harder soil, are 3/4 inch in diameter as opposed to 5/8-inch rods which dominate in the United States.
The length of a ground rod plays a much bigger role in its final ground resistance measurement, and it goes without saying that it takes longer to drive a longer ground rod.
The NEC and UL require a ground rod to be at least 8 feet in length. This specification was obviously created by engineers that had never driven a ground rod or noticed that most people are not 8’ tall. Longer rods are more dangerous to install and bow more when being driven.
The more a rod bows or shudders, the less efficient the driving process is. Shorter rods are safer and easier to drive. In fact, I would love to see the industry standardize on using two 4-foot rods and a coupler to achieve the required 8 feet total length. Installations would be faster, easier, and safer not to mention that the logistics of transporting and storing a 4-foot rod are much simpler than longer 8- or 10-foot rods.