I work for 3M as an electrical engineer and during a design review we had a debate on what is exactly considered a current carrying conductor for the purpose of derating, pertaining to T310.15(B)(2)(a). A standard I/O module is only rated for 2A and is typically fused at 5A. So most of the devices connected to an I/O module such as a solenoid valve, a level switch, a proximity switch, etc. has very little current flowing through the conductors connected to that device. Is there a specific article, section, or exception in the code that states certain devices do not have to be considered current carrying conductors when derating. Any help that you can offer in this issue would be greatly appreciated.