As I look through the code, it never says that a grounded conductor can or can't be smaller or larger than the gec. When I compare the 250.66 table to .102(C)(1) table, it shows me the grounded conductor will be the same size or larger. When reading about the gec, it says how small it can be. Such as, it never has to be larger than a #6awg CU to a ground rod. My takeaway is the grounded conductor can never be smaller than the gec. Am i missing something?
The terms grounded conductor and grounding conductor can be very confusing. It helps to cross reference them to their more common terms.
GroundED conductor = more commonly called a neutral, and 9 times out of 10, this will be the neutral. There are occasions where there is a reason to tell these two terms apart, but that's another topic.
GroundING conductor = commonly called a ground, but formally known as an equipment grounding conductor (EGC). This wire is green or bare, and has the purpose to bond together all electrically inactive metal, with a fault current path back to the source.
GroundING electrode conductor (GEC) = a conductor for connecting to the electrode in the dirt, so that both the neutral and EGC systems are at the same absolute voltage as the soil.
It's true that the grounded conductor can neve be smaller than the EGC, or other green or bare wire that may take the place of an EGC (like an SSBJ, for transformer secondaries). The grounded conductor has to at least be large enough for the current it must carry, and commonly is full size. But if it carries negligible current, the minimum size is to match the green wire's size, whether it's a 250.122 EGC, or a 250.102 SSBJ that applies. The GEC is out of the picture for its sizing. It's the green wire routed with the circuit, rather than the green wire routed off to the side to the ground rod, that matters.
