For a grounding electrode, which underground metal piping should meet the minimum requirements?

The correct choice regarding the type of underground metal piping that meets the minimum requirements for a grounding electrode is steel pipe.

Steel pipe is conductive, allowing it to effectively serve as a grounding electrode. The fundamental purpose of grounding electrodes is to provide a low-resistance path to ground for fault currents and lightning strikes, aiding in the protection of electrical systems and reducing the risk of electric shock.

Brass and copper pipes are also conductive, but they are not typically recognized or preferred for grounding electrode systems in the same manner as steel. Brass can corrode more easily than steel when buried and exposed to certain soil conditions. Plastic pipe, on the other hand, is non-conductive and does not provide any grounding capabilities, making it unsuitable for this application.

Thus, steel pipe, with its durability and conductivity, is recognized as an appropriate choice for grounding in accordance with electrical codes and standards.