Because running cable inside a finished wall is impractical in this situation (there is no attic and access to the floor below is difficult), I'm planning on installing a surface mounted raceway. Inside this raceway, I would like to put

  • 2 X 20A dedicated circuit for window/portable air conditioners
  • 1 X 15A circuit for outlets.

Two questions:

  • Do I use THHN wire for this or can I run sheathed cable inside the raceway? From what I've read, THHN is better because of heat dissipation but I'm not sure.
  • Do I have to derate? It seems that I have more than three conductors (3 hots + 3 neutrals).

For code purposes: Quebec, Canada

  • Have you selected the surface raceway product, and, if so, what is it? I just saw a video of a nifty crown molding raceway which could give a very nice result. youtube.com/watch?v=iLCVIrlBH4I – Jim Stewart Jul 25 '18 at 15:11

Yes, but the derate won't actually hurt. What applies is the lowest of all the derates, and they are several. This one is that with 4-6 wires, you derate to 80% of the 90 degree C column of Table 310.15(B)(16). So your 14 AWG wire must be derated to 20A, and 12 AWG wire must be derated to 24A.

I'm guessing that won't ruin your plans.

As far as NM vs THHN, NM takes a lot more space, you run into conduit fill issues sooner. It's also a great deal stiffer than individual THHN wires. You may think THHN is just as stiff as individual wires of Romex, however they also make stranded THHN, which is much more flexible and easier to work with.

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