Electrical – Using leftover Romex in conduit (surface mount application in an attached garage)

electrical

I am planning to add an outlet circuit to my garage. Strangely, when they built the house, they only put two outlets in the entire garage, both of which are on shared circuits with the rooms on the other side of the wall (living room and kitchen). I have more than 100 feet of 12-2 Romex left over from other wiring projects, and wanted to know what my options were for using it in a surface mount application. I really don't want to open the walls up in the garage. Quick research indicates that it's NOT against code to run Romex in conduit, but it's not best practice for heat dissipation purposes and can be a pain to pull. I know THHN is relatively cheap, but not if I need to buy 3 separately colored spools of it rather than buying one larger spool and remarking the wires (which is against code, correct?)

Thanks,

Best Answer

You need big conduit

A flat cable like Romex is treated the same as a circular wire of the large dimension.

  • With 1 cable in round conduit, the conduit inside diameter must be at least 138% of the widest cable width.
  • With two same cables in round conduit, the conduit ID must be 259% of the widest cable width.
  • with three same cables in round conduit, the conduit ID must br 274% of the widest cable width.

Note that at minimum sizes, it will be a bugbear to pull. You may be wise to upsize further for ease of pulling.

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If you are using non-round conduit, then you need to look up the cross sectional area of the conduit and compute the cross section of the (rounded out) cable. Compute

cross section of cable = (cable widest width ^ 2) * 3.14159 / 4

Cable cross section can't exceed 53% of cable cross section for 1 wire in conduit; 30% for 2 cables in conduit, and 40% for 3 or more.

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