Is there a website where I can access the complete and most recently updated version of the United States NEC for free?
Yes, the NEC. Is free once adopted . search for free NEC and you will find it. This is only for the "code" I don't think they release the hand book that has a lot of information on why, this is the version most inspectors use , but once adopted the NEC is free on line. Just checked look up nfpa.org free access just need to sign in..