Between transmission and distribution, which requires the larger minimum ground size?

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Sizing the minimum ground size is driven by how much fault current the equipment can produce and how the grounding system needs to limit voltages during a fault. It’s not fixed by whether something is transmission or distribution; the key factor is the specific equipment’s grounding requirements, fault current levels, and protection strategy, all of which can vary by installation.

In practice, the grounding grid and conductor sizes are chosen to carry the expected fault current safely, minimize step and touch voltages, and meet protective device operating times. A high-voltage transmission setup often has higher fault currents and therefore can require a larger, more robust ground grid, but certain distribution equipment or arrangements with high fault duties can also demand substantial grounding. Conversely, some equipment or sites may have lower fault currents and smaller grounding needs.

So the correct idea is that the minimum ground size depends on the equipment and its fault characteristics, not simply on whether it’s part of transmission or distribution.