What must be true of all grounding electrodes at each building or structure served by electricity?

For any building or structure that is served by electricity, it is essential that grounding electrodes are present. Grounding electrodes are vital for electrical safety, as they provide a direct path for electrical faults to earth, helping to prevent electric shock hazards and equipment damage.

The requirement for grounding electrodes is outlined in the National Electrical Code (NEC), which specifies the need for effective grounding systems to ensure electrical installations are safe. Without grounding electrodes in place, the risk of electrical faults could lead to dangerous conditions such as electrical fires or shock hazards for individuals interacting with electrical systems.

In contrast, the other options do not encompass the critical safety provisions required by the NEC. Convenience does not dictate the presence of grounding electrodes, simply being "unavailable" is not an acceptable condition for safety, and while proximity is important in many aspects of electrical installations, it is not a requirement for ensuring the safety and effectiveness of grounding electrodes. Thus, the presence of grounding electrodes is a fundamental requirement for any electrical service in buildings or structures.