Conduit Fill Limits

Per NEC Chapter 9, the percentage of a conduit's cross-sectional area that can be occupied by cables is restricted to prevent overheating and physical damage during pulling.

NEC Fill Limits

Number of Conductors	Maximum Fill %
1	53%
2	31%
3 or more	40%

Jam Ratio Warning

When pulling 3 cables/wires, if the ratio of the conduit inside diameter to a single cable outside diameter is between 2.8 and 3.2, the cables may align in a flat plane and jam in bends. Avoid this ratio.

Interactive calculator requires JS. For manual calculation, sum the area of all cables and compare against 40% of the conduit's inner area.