Conduit can only be filled to 40% with three or more conductors, to allow heat dissipation and pulling. This chart gives the max number of THHN conductors for common EMT sizes.
| EMT conduit | 12 AWG THHN | 10 AWG THHN |
|---|---|---|
| 1/2 in | 9 | 5 |
| 3/4 in | 16 | 10 |
| 1 in | 26 | 16 |
| 1-1/4 in | 45 | 28 |
Watch derating too. When more than three current-carrying conductors share a conduit, their ampacity must be derated. Always follow NEC fill and derating tables for your wire type.
FAQ
Why does conduit fill percentage matter? Conduit fill limits (commonly 40 percent for three or more conductors) leave room to pull wires without excessive friction or damage to insulation, and allow some airflow for heat dissipation, both of which get worse as fill percentage increases.
See the Electrical Box Fill Chart and Wire Ampacity Chart.
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