I remember a few years back being called on having a duplex outlet on a designated circuit. It was for a microwave. The inspector made me change out all of my designated outlets to single outlets. hat does the code say about that in resi applications. TY
NEC requirements for using a single outlet has been miss understood by many over the years.
The only place the NEC required a single outlet was where GFCI protection was required and a single outlet could be used to meet an exception, I seen inspectors requiring them for dishwashers, disposals, microwaves, and even garage door openers, but in reality in the past all of these never was require to be protected by a GFCI so there was no exception to meet.
Now some of this has change with the removal of the GFCI exception's in the 2008 code cycle, with the removal of these exceptions, the requirement of single receptacles also went out the door.
Now some will say that the requirements in 210.23 can require that a single receptacles must be used but I have yet seen this proved, as it only gives us guide to how much load is allowed to be plugged in, no where does it say a single receptacle must be installed.