NEC Commercial Electrical Practice Test

A metal underground water pipe used as a grounding electrode must be in direct contact with the earth for at least how many feet?

1. 5 feet

2. 8 feet

3. 10 feet

4. 15 feet

The correct answer is: 10 feet

A metal underground water pipe used as a grounding electrode must be in direct contact with the earth for at least 10 feet to ensure effective grounding. This requirement, outlined in the National Electrical Code (NEC), reflects the need for grounding electrodes to have a sufficient length in direct physical contact with the earth to achieve a low resistance path for electrical faults. Grounding is critical for safety and to protect electrical systems from surges or faults. A longer length of contact with earth increases the surface area in which the grounding electrode can dissipate electrical currents, minimizing risks associated with electric shock or equipment damage. In practical scenarios, having at least 10 feet of contact can contribute to better grounding performance in various soil conditions, making it less susceptible to changes in soil resistivity due to moisture, temperature, or seasonal variations. This 10-foot requirement is a crucial part of ensuring that the grounding system is robust and meets safety standards within electrical installations.