EGC Proportional Upsize for Increased Conductors (NEC 250.122(B))
When ungrounded conductors are increased in size for voltage drop or future capacity, the equipment grounding conductor increases in the same circular-mil proportion per NEC 250.122(B). Base EGC and base phase area are user-supplied table values; the EGC need not exceed the ungrounded conductors. The AHJ governs.
Formula and source
ratio = max(1, installed_phase_cmil / base_phase_cmil); upsized_EGC_cmil = base_EGC_cmil x ratio, then select the next standard AWG/kcmil at or above this. A ratio below 1 is clamped to 1 (the EGC is never reduced below its table size).
NEC 2023 (NFPA 70). 250.122(B) (increase in size of equipment grounding conductors).
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