Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsMedium
A residential electrician is installing a new 120-volt, 20-amp branch circuit for kitchen counter receptacles. The circuit will be run through a 1/2-inch EMT conduit. According to NEC Table 310.16, if using THHN insulated conductors, what is the maximum number of 12 AWG conductors permitted in this conduit, assuming no derating for ambient temperature or number of current-carrying conductors is required?
- A7
- B9
- C5
- D6
Show answer & explanationAnswer & explanation
Correct answer: B. 9
NEC Table C.1 for 1/2-inch EMT conduit with THHN conductors specifies a maximum of 9 #12 AWG conductors. This table accounts for conductor insulation type and conduit size to determine fill.
Why the other options are wrong
- A. Incorrect. This number is too low for 1/2-inch EMT with #12 THHN conductors.
- C. Incorrect. This number is too low for 1/2-inch EMT with #12 THHN conductors.
- D. Incorrect. This number is too low for 1/2-inch EMT with #12 THHN conductors.
Conduit Fill for THHN
The maximum number of conductors permitted in a conduit is determined by the conduit's trade size, the conductor's size (AWG), and the insulation type.
- NEC Chapter 9, Tables C.1 through C.12, provide specific fill capacities for various conduit types and insulation.
- THHN insulation generally allows for more conductors due to its smaller overall diameter compared to other types.
- Conduit fill limits prevent overheating and allow for easier pulling of conductors.
Memory trick: Fill the pipe right, or circuits take flight!