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.

Look at Exception #1 to 310.15(B)(2).
Don

NFPA70 (the NEC) is for premises wiring not for machinery. NFPA79 (Electrical Standard for Industrial Machinery) may be more appropiate for your application. The scope of NFPA79 includes: "...systems of industrial machines...commencing at the place of connection of the supply..."

Some major differences between the two standards:
minimum circuit wire size; NEC-#14, NFPA79-#24 (in raceway)
maximum raceway fill; NEC-40%, NFPA79-50%
drain holes in raceways; NEC-not allowed, NFPA79- upto 1/4"
raceway as grounding or bonding conductor; NEC-allowed; NFPA70 - not allowed

[This message has been edited by JBD (edited 03-10-2003).]