Final answer:
Grounding is the process of connecting a conductor to the Earth to fix it at zero volts. Metal underground water pipes, metal underground gas pipes, the metal frame of a building, and a ground ring can all be used as grounding electrodes.
Step-by-step explanation:
Grounding is the process of connecting a conductor to the Earth with a good conductor to fix it at zero volts. The allowed materials for grounding electrodes include metal underground water pipes, metal underground gas pipes, the metal frame of a building, and a ground ring.