PG&E routinely uses undersized neutrals:
1000 KCmil hots (3)
350 KCmil neutral (1)
no ground bond
3 phase system.
per pipe... each 5" (EUSERC) last job only 3 out of 8 pipes had wire.
The MAIN was set at 2,000 Amps
This enters a EUSERC big box from below slab... with dependent Services at 400, 400, and a string of 200's
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I've installed 3 phase panels with massive 3 phase rotary loads.
1100 Amps in a 1200 Frame chassis -- four raceways with a massive Al bonding wire ( 1100 Amps ) while the largest possible unbalanced load was 90A resulting in a dinky neutral.
Reducing the Service neutral is entirely determined by the Poco -- it's outside the scope of the NEC. That hunk of wire is going to be deeded over to the Poco and become their liability for performance.
Because of those dynamics, it's almost never worth the hassle of even raising the topic -- unless it's been established on the approved one-line submitted at the beginning.
The answer to this issue is never to be found in the NEC. It's a Poco thing. They have their standards -- and they don't give a dang what the NEC says.
