What You Need to Know About Grounding

Q We recently replaced a 13.8 KV, 2000 KVA transformer that was installed in the early 1950s. The earth ground conductors are embedded in a concrete slab. Construction personnel told me that they only test for earth ground on new substations and not on those over 50 years old. Is there an NEC requirement (or intent) to perform a ground resistance test on transformer replacements of this kind?