Oklahoma Electrical Practice Exam

When using a metal underground water pipe for grounding, what is the minimum length that must be in contact with the earth?

1. 5 feet

2. 8 feet

3. 10 feet

4. 12 feet

The correct answer is: 10 feet

The minimum length of a metal underground water pipe that must be in contact with the earth for grounding purposes is 10 feet. This requirement is set to ensure that there is a reliable and effective ground connection, which is crucial for safety in electrical systems. The rationale for the 10-foot specification is based on the need for adequate contact area with the earth to provide a low-resistance path for fault currents, thereby helping to dissipate electrical energy safely into the ground. If the length were shorter, there could be insufficient grounding effectiveness, potentially leading to safety hazards such as electrical shock or equipment damage. Proper grounding is a critical component of electrical installation practices, and using a metal underground water pipe appropriately can significantly enhance the reliability of the grounding system when the specified length is observed.