What is the required resistance to ground for an effective ground using an 8' ground rod?

For an effective ground system, particularly when using an 8-foot ground rod, the generally accepted industry standard specifies that the resistance to ground should be 25 ohms or less. This threshold ensures that the grounding system can adequately protect both personnel and equipment by providing a low-resistance path for fault currents or surges.

A resistance value of 25 ohms or less is significant for ensuring the effectiveness of grounding in various conditions, including those that can arise from lightning strikes, electrical faults, or other disturbances. Lower resistance values can lead to improved performance and safety of electrical systems, which is particularly crucial in outdoor settings where environmental factors can impact grounding effectiveness.

The requirement of 25 ohms takes into account the practicality and feasibility of achieving a low enough resistance level without necessitating overly complex or extensive grounding installations. Thus, selecting this value reflects both regulatory standards and practical considerations for effective grounding in outside plant environments.