In which situation would multiple grounding electrodes be necessary?

Multiple grounding electrodes are necessary in situations where the soil resistivity is high. High soil resistivity can hinder the effective dissipation of fault currents and can result in inadequate grounding. This is crucial because a well-grounded system plays a key role in protecting both people and equipment from electrical faults.

When soil has a high resistivity, it is less capable of conducting electrical current, which may lead to a poor ground connection. To overcome this challenge, installing multiple grounding electrodes can help achieve a lower overall resistance to ground. This can ensure that electrical faults are effectively managed and that the grounding system maintains safety and functionality.

In contrast, the other situations presented would not typically necessitate multiple grounding electrodes. For example, when equipment is located indoors, the grounding requirements may be different, and the conditions could potentially allow for a single electrode. Similarly, ungrounded systems do not rely on grounding electrodes for safety, and a solidly grounded system implies a sufficient grounding path that may not require multiple electrodes. Thus, high soil resistivity remains a critical factor in determining the need for multiple grounding electrodes.