NFPA 79 control box wire size

[jimmalik]

I have worked at several companies and everyone has a different interpetation of the NFPA 79 code for wire size in control box and on machine wiring. My current company is using 20AWG (UL not printed on wire also)inside the box from PLC to terminal blocks. And use 24AWG cable from box to descrete devices(sensors, etc).
I am talking about DC. I have always used 18AWG. Why can't they make the code cut and dry. Can someone clarify this as to code and not personal/company preference.

Jim

 

[dV8r]

It's not interpretation or preference, it is absolut. It is all about current carrying capability, heat disipation and voltage drop. Maybe not simple calculations but calculations non the less.