NEC Commercial Electrical Practice Test

How deep must plate electrodes be exposed below the surface of the earth?

1. 12 inches

2. 18 inches

3. 24 inches

4. 30 inches

The correct answer is: 24 inches

Plate electrodes must be buried at a depth of 24 inches below the surface of the earth to ensure proper grounding. This depth is specified to enhance the connection between the electrode and the surrounding earth, which is critical for effective grounding. Adequate penetration into the earth allows the electrode to achieve a low resistance to ground, which is essential in preventing electrical shock hazards and ensuring the safety of electrical installations. Additionally, this depth helps protect the electrode from physical damage and environmental conditions that may alter its performance, such as frost or soil movement. The 24-inch requirement aligns with the National Electrical Code (NEC) standards, which are designed to promote safety and reliability in electrical systems.