Three or more conductors may fill 40 percent of a raceway area (NEC Chapter 9, Table 1). For 12 AWG THHN that is 9 in 1/2 in. EMT and 16 in 3/4 in. EMT.
The smallest EMT that takes 9 conductors of 12 AWG THHN is 1/2 in. 9 conductors fill 39 percent of 1/2 in. EMT.
Most 12 AWG THHN conductors per trade size, EMT
Trade size (in)
40 percent area (sq in)
Most conductors
1/2
0.122
9
3/4
0.213
16
1
0.346
26
1-1/4
0.598
45
1-1/2
0.814
61
2
1.342
101
2-1/2
2.343
176
3
3.538
266
3-1/2
4.618
347
4
5.901
443
Same-size conductors only. Mixed sizes add each conductor area from Chapter 9, Table 5 and compare it with the percent in Table 1. Other insulation types are larger or smaller; check their areas.
