earlydean,

I disagree with your _literal_ interpretation of the NEC, though not on your read of intent, nor the safety of the installation that you describe.

310.4 is written to _permit_ parallel conductors sized 1/0 AWG or larger, and then has several exceptions that permit smaller conductors to be paralleled. (310.4 Exception 2 clearly matches what you describe, but only for limited types of circuits.) The pretty clear _implication_ is that parallel conductors smaller than 1/0 AWG, not covered by the exceptions, would therefore be prohibited.

I do not find any _explicit_ prohibition of smaller parallel conductors. Since the NEC is supposed to be a permissive code, this itself causes some problems with interpretation [Linked Image]

300.3(B) has its own problems. It does not explicitly permit switch loops (and most switch loops don't have a neutral), and 'circuit' is not defined in article 100 ('Branch circuit' is defined, but 300.3(B) clearly applies to feeders as well as branch circuits.) The common _understanding_ of 300.3(B) is that the net current flow of all conductions in a raceway must balance out to zero, thus permitting switch loops. But this is not what the code actually says.

-Jon