What is the maximum allowable resistance for a grounding electrode according to the NEC?

The maximum allowable resistance for a grounding electrode according to the National Electrical Code (NEC) is indeed 25 ohms. This standard is established to ensure that the grounding system is effective in providing a low-resistance path to ground. A grounding electrode with a resistance of 25 ohms or less is considered sufficient for dissipating fault currents safely into the earth, which minimizes the risk of electrical shock and equipment damage.

Setting the maximum resistance value at 25 ohms serves to enhance safety by ensuring that any faults in the electrical system have a reliable path to ground, helping to trip circuit breakers or blow fuses promptly and thereby reducing the chance of fire or electrocution. In practice, while it’s ideal to achieve a reading lower than 25 ohms, this value is the threshold that must not be exceeded to meet code requirements.