Conduit fill (Chapter 9)

Fill a raceway — choose the raceway type and a trade size (or Smallest that fits), and tick nipple for a run of 24 in or less. Add the conductors: insulation (THHN/THWN-2, XHHW-2, THW, RHW-2, TFFN fixture wire, bare stranded or solid), size, how many and a colour for the drawing. A cable counts as one conductor of its outside diameter. The bar at the top shows the fill against the limit and stays in view; below are the cross-section, the areas, the jam ratio when there are exactly three conductors, and the smallest size of every raceway type for the same conductors.

How many fit — the most conductors of one insulation and size in each trade size, the way the Informative Annex C tables are built, with the nipple figure and the jam ratio.

Related: wire size and voltage drop (bundling corrections for more than three current-carrying conductors), box fill, grounding and bonding sizes, the shop power planner and the wire gauge table.

Raceway areas are Chapter 9 Table 4, conductor areas Table 5 (insulated) and Table 8 (bare), and the limits Table 1: 53 % for one conductor, 31 % for two, 40 % for three or more; 60 % for nipples (Note 4). The count of one size is 40 % of the area divided by the conductor’s area, rounded up when the decimal is 0.8 or more (Note 7). The jam ratio is the raceway’s inside diameter over the conductor’s diameter (derived from its Table 5 area); 2.8 to 3.2 is the risky band. The drawing packs the conductors by a simple simulation, so it is a picture, not a proof.

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