See 230.90(A)- "Such protection shall be required by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor..."
Now look at exception number 2. This exception allows the service conductors to be smaller than the ampacity of two to six service disconnects provided that the service conductors are large enough for the total calculated load. In short, when there is only one service disconnect, the service conductors must be fully sized based on the service overcurrent device.
Electrical Inspector, Plans Examiner, Code Instructor
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