What is the maximum resistance to ground for a single electrode, below which a supplemental electrode is not required?

The correct answer is based on the guidelines set forth in the National Electrical Code (NEC) regarding grounding and bonding requirements for electrical systems. A single electrode used for grounding, such as a ground rod, has a specified maximum resistance to ground, and it is essential for ensuring the safety and functionality of the electrical system.

In this case, a maximum resistance of 25 ohms indicates that if the resistance to ground for the single electrode is 25 ohms or lower, no additional supplemental electrode is needed. This threshold is established to ensure that the grounding system is effective in dissipating fault currents and providing a low-resistance path to ground, which is crucial for both safety and equipment protection.

If the resistance exceeds this limit, the grounding system may not adequately protect against electrical faults, which could lead to hazardous conditions such as electric shock or equipment damage. Thus, recognizing that 25 ohms is the critical cutoff ensures compliance with safety standards and the effective operation of electrical systems.