Originally Posted by WillK
Er.. okay. So maybe I'll just do a switch in the garage I guess and leave cables so I can use them later to pull 14/3 if I change my mind later this month..
But for my own curiousity, what difference does it make to 3 conductors if they are inside the same plastic sheathing or not? And for that matter wouldn't it be allowed to run 3 THHN conductors?
its an obscure code section, actually two sections that work together(or not).
Essentially what is says is that all conductors of a circuit must be in one cable or pipe(so yes thhn would work). It is because of induction and eddy currents created in metal. There is an "exception" using only certain cables(NM), that if completely non metallic (romex, wood studs, plastic boxes) that you are allowed to use more than one piece of romex for a circuit(note this is subject to some intereptation, some say that there is no exception to the rule for all circuit conductors to be run together. its one of those things that the code doesn't say you can, but doesn't explicatively say you can't)
I'm sorry I don't have the code sections in front of me, but this topic has been hammered out pretty throughly on this and other forums before.
edit: ever wonder why 2 wire w/ground romex is flat
? three wires twist into a nice round shape. why 3 wire is round and twisted at that certain rate? these cables are designed
to work as a unit
, for many purposes one of which is to reduce induction/noise/eddy currents. this is one reason that the code does not allow you to modify cables or use them for purposes not listed in the code. cables have been engineered in so many ways, that you just can't contemplate them all if you are trying to use it outside of the manufactures instructions.
If you fail to run all circuit conductors in the same path/pipe/cable, you can get many undesired effects: eddy currents, high impedance, radio interference, oh help me out guys list the other effects. eddy currents could build up enough in metal objects enough to be dangerous.