I know all all of those articles but where does it state the ocpd can be rated higher than the branch circuit. all it states is the branch circuit is to be selected from the table or from the nameplate which states "Minimum" branch circuit selection. I dont see anywhere in article 440 (which is where it would need to be) that the ocpd can be higher than the rated current capacity stated in 310.15 for the choosen branch circuit. it does state the ocpd must be rated at least 115% above the minimum branch circuit selection but it doesnt state that it can be rated higher than the branch circuit you select. IM not aruing, I am wanting to agree with you and be able to size the wire smaller than the CB but I need a definetive code reference that states I can do that.
The general rule is that conductors need protected at their rated ampacity ? or next higher standard size overcurrent device. As I pointed out 240.3 list several other articles that may have exceptions to the general rule.
For the air conditioning equipment you mention we go to Art 440.
Three different parts of 440 come into play here.
- Branch-Circuit Short-Circuit and Ground-Fault Protection
- Branch-Circuit Conductors
VI. Motor-Compressor and Branch-Circuit Overload Protection
Each part tells us the requirements for that particular item and does vary from what is generally required in chapters 2 and 3.
When all three of these parts are applied you still end up with a conductor large enough to supply the load without overheating, you have short circuit and ground fault protection, and you have overload protection, so the conductor is protected from overcurrent and the resulting overheating, it is just done so with more than one device. Article 430 for motors accomplishes the same thing in a similar fashion in many installations.
Almost any equipment that has an inrush current when energized will have similar requirements.
There are instances that are more specialized like a fire pump. With a fire pump they want short circuit and ground fault protection but want the motor to run even if overloaded as the purpose of the pump running is likely more important than having it shut down because it is overloaded.
Hope this helps you understand. This could get lengthy to tell all the places where higher size overcurrent device than general rules allow may exist but the idea is about the same with most of them.