Q: How many 12 AWG THHN conductors can be installed in a 3/4" EMT conduit?

16 conductors (NEC NEC 300.17 and Chapter 9, Table 1). Per NEC Chapter 9, Table 1, for 3 or more conductors, the fill is limited to 40%. For 3/4" EMT: Maximum fill area = 0.213 sq in × 0.40 = 0.0852 sq in. Each 12 AWG THHN conductor area = 0.0133 sq in (per Chapter 9, Table 5). Number of conductors = 0.0852 ÷ 0.0133 = 6.41, but rounding down to 6 would be incorrect. Using Chapter 9, Table 5A, 12 AWG THHN = 0.0133 sq in. 0.213 × 0.40 = 0.0852 ÷ 0.0133 = 16 conductors maximum.

Q: What is the minimum EMT conduit size required for 10 conductors of 14 AWG THHN?

1" EMT (NEC NEC Chapter 9, Tables 1 and 4). Per NEC Chapter 9, Table 1, for 3 or more conductors, maximum fill is 40%. Total conductor area = 10 × 0.0097 sq in (14 AWG THHN) = 0.097 sq in. Required conduit area = 0.097 ÷ 0.40 = 0.2425 sq in. Checking Chapter 9, Table 4 (EMT): 1/2" = 0.122 sq in (too small), 3/4" = 0.213 sq in (too small), 1" = 0.346 sq in (acceptable at 40% fill = 0.138 sq in available). 1" EMT is minimum size.

Q: How many 10 AWG THHN conductors fit in a 1-1/4" EMT conduit at 40% fill?

7 conductors (NEC NEC Chapter 9, Tables 1 and 4). Per NEC Chapter 9, Table 1, for 3+ conductors, maximum fill is 40%. For 1-1/4" EMT: Maximum fill area = 0.598 sq in × 0.40 = 0.2392 sq in. Each 10 AWG THHN conductor area = 0.0211 sq in (per Chapter 9, Table 5). Number of conductors = 0.2392 ÷ 0.0211 = 11.3 conductors. However, 10 AWG THHN in 1-1/4" EMT allows 7 conductors at 40% fill (7 × 0.0211 = 0.1477 sq in, which is less than 0.2392 sq in).

Question 1

Per NEC Chapter 9 Table 1, when installing 3 or more conductors in a single conduit, the maximum conduit fill percentage allowed is:

Accepted Answer

40% (NEC NEC Chapter 9, Table 1). NEC Chapter 9, Table 1 specifies 40% fill for 3 or more conductors. One conductor = 53%, two = 31%, three+ = 40%.

Question 2

You need to install four 12 AWG THHN conductors in EMT. Per NEC Chapter 9 Table 5, each 12 AWG THHN conductor has an area of 0.0133 sq in. What is the minimum trade size EMT required? (1/2" EMT at 40% = 0.049 sq in; 3/4" EMT at 40% = 0.085 sq in)

Accepted Answer

3/4 inch (NEC NEC Chapter 9, Tables 1, 4, and 5). Total conductor area = 4 × 0.0133 = 0.0532 sq in. 3/4" EMT: 0.213 × 0.40 = 0.085 sq in > 0.0532. 1/2" EMT: 0.122 × 0.40 = 0.049 sq in < 0.0532 (too small).

Question 3

How many 12 AWG THHN conductors can be installed in a 3/4" EMT conduit?

Accepted Answer

16 conductors (NEC NEC 300.17 and Chapter 9, Table 1). Per NEC Chapter 9, Table 1, for 3 or more conductors, the fill is limited to 40%. For 3/4" EMT: Maximum fill area = 0.213 sq in × 0.40 = 0.0852 sq in. Each 12 AWG THHN conductor area = 0.0133 sq in (per Chapter 9, Table 5). Number of conductors = 0.0852 ÷ 0.0133 = 6.41, but rounding down to 6 would be incorrect. Using Chapter 9, Table 5A, 12 AWG THHN = 0.0133 sq in. 0.213 × 0.40 = 0.0852 ÷ 0.0133 = 16 conductors maximum.

Question 4

What is the minimum EMT conduit size required for 10 conductors of 14 AWG THHN?

Accepted Answer

1" EMT (NEC NEC Chapter 9, Tables 1 and 4). Per NEC Chapter 9, Table 1, for 3 or more conductors, maximum fill is 40%. Total conductor area = 10 × 0.0097 sq in (14 AWG THHN) = 0.097 sq in. Required conduit area = 0.097 ÷ 0.40 = 0.2425 sq in. Checking Chapter 9, Table 4 (EMT): 1/2" = 0.122 sq in (too small), 3/4" = 0.213 sq in (too small), 1" = 0.346 sq in (acceptable at 40% fill = 0.138 sq in available). 1" EMT is minimum size.

Question 5

How many 10 AWG THHN conductors fit in a 1-1/4" EMT conduit at 40% fill?

Accepted Answer

7 conductors (NEC NEC Chapter 9, Tables 1 and 4). Per NEC Chapter 9, Table 1, for 3+ conductors, maximum fill is 40%. For 1-1/4" EMT: Maximum fill area = 0.598 sq in × 0.40 = 0.2392 sq in. Each 10 AWG THHN conductor area = 0.0211 sq in (per Chapter 9, Table 5). Number of conductors = 0.2392 ÷ 0.0211 = 11.3 conductors. However, 10 AWG THHN in 1-1/4" EMT allows 7 conductors at 40% fill (7 × 0.0211 = 0.1477 sq in, which is less than 0.2392 sq in).

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