THHN Conductors and RMC

Question: How many #12 THHN conductors can I install in a 3/4″ rigid metal conduit?

Answer: The simple way to obtain this information is to refer to Annex C, Table C8 in the NEC. Find “THHN” in the left-hand column, and find trade size 3/4 across the top of the Table. The answer is “16”.

NEC Article 344 covers rigid metal conduit. Section 344.22 states: “The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9. (40%).”

You can make your own calculations using Tables 4 and 5 in Chapter 9. However, where all of the conductors are the same size, it is easier to use Annex C; Annex C Tables are based on Table 1, Chapter 9 and incorporate the calculations.