NEC Commercial Electrical Practice Test

When using plate electrodes for grounding, how much surface area must be exposed to exterior soil?

1. One square foot

2. Two square feet

3. Three square feet

4. Four square feet

The correct answer is: Two square feet

The requirement for grounding electrodes, specifically plate electrodes, is to ensure adequate surface area is in contact with the earth to facilitate effective grounding. According to the National Electrical Code (NEC), a grounding plate must have a minimum of two square feet of surface area exposed to the exterior soil. This threshold allows for sufficient dissipation of electrical energy into the ground, contributing to the safety and efficacy of the grounding system. Having two square feet of contact ensures that the electrode has enough surface area to interact efficiently with soil, which typically has varying resistivity based on moisture content and composition. More exposure increases the interaction with the earth, helping to reduce electrical resistance and improve the overall grounding system's performance. This is crucial for protecting both equipment and personnel from electrical faults. The options that suggest one, three, or four square feet do not meet the NEC minimum requirement for this type of grounding electrode. While larger areas can provide better grounding, the minimum stipulated by the NEC is two square feet, emphasizing the balance between sufficient grounding and practical installation standards.