May have been covered before but... An inspector told me today that a 15 amp duplex receptacle is not allowed on a 20 amp dedicated circuit. From what I read in the book this would be allowed 210.21(b)(1), (3)because this is not a "single receptacle" as defined by the NEC. He didn't push the issue and signed off on the job but for future reference I would like to hear other opinions.

You're right.