What type of grounding electrode must be used at each new building or structure on a permanent concrete foundation?

The correct answer is a concrete encased grounding electrode. In Washington State, and according to the National Electrical Code (NEC), structures that have a permanent concrete foundation should utilize an encased grounding electrode system. This grounding method typically involves using a rebar or a wire mesh that is embedded within the concrete of the foundation.

The rationale for this requirement lies in the relatively high level of effectiveness that a concrete encased electrode provides in terms of safety and reliability. Such an electrode is directly in contact with the earth due to its placement within the concrete, which helps to ensure adequate grounding and bonding of electrical systems to protect against electrical faults and surges.

Other grounding methods, like a steel grounding rod, copper plate grounding, or direct burial grounding wire, do not fulfill the specific requirement for new buildings with concrete foundations as effectively as the encased grounding electrode. These methods may be suitable in other contexts or as supplementary systems, but they do not meet the specific code requirements for structures on permanent concrete foundations, which prioritize durability and long-term performance.