NEC Commercial Electrical Practice Test

If a single made rod, pipe, or plate electrode has less than 25 ohms resistance to ground, what must be done?

1. No additional electrodes are needed

2. One additional electrode must be installed

3. Two additional electrodes must be installed

4. The system must be redesignated

The correct answer is: One additional electrode must be installed

The correct answer is that no additional electrodes are needed if a single made rod, pipe, or plate electrode has less than 25 ohms resistance to ground. According to the National Electrical Code (NEC), the primary concern when grounding is ensuring that there is a low enough resistance to facilitate fault current flow, which minimizes the risk of electric shock and equipment damage. When the resistance to ground for a single electrode is below 25 ohms, it meets the NEC requirement for effective grounding. This means that the ground is sufficiently low-resistance, and there is no need to increase the grounding system with additional electrodes. The requirement for additional electrodes typically applies when the resistance exceeds this threshold, implying that enhancing the grounding system would help achieve the necessary safety standards. This grounding threshold is particularly important in electrical safety practices, ensuring that equipment is reliably protected, and users are safeguarded from electrical faults. Thus, an electrode with a resistance lower than 25 ohms is considered adequate, and there is no obligation to install more electrodes in that scenario.