According to codes, what is the maximum resistance allowed for a driven ground?

The maximum resistance allowed for a driven ground is set at 25 ohms. This standard is established to ensure effective grounding, which is crucial for safety in electrical systems. A grounding resistance of 25 ohms or less helps to minimize the voltage that can appear on the earth during fault conditions, thereby reducing the risk of electric shock to individuals and equipment damage.

Grounding systems must be designed to ensure that they can effectively dissipate fault currents. If the resistance exceeds 25 ohms, it may not provide adequate safety protection during a fault scenario, potentially allowing dangerous voltages to persist. This standard is part of various electrical codes and standards, which aim to ensure the reliability and safety of electrical installations.

Other values listed, such as 15, 35, and 45 ohms, do not comply with the safety requirements outlined in current codes, thereby making 25 ohms the maximum acceptable limit for effective grounding.