CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A material takeoff for a new residential construction includes several 120V, 15A lighting branch circuits. The plans specify using 14 AWG THHN conductors. What is the maximum number of 14 AWG THHN conductors permitted in a 1/2-inch trade size EMT conduit, assuming all conductors are current-carrying?
- A12
- B7
- C10
- D9
Show answer & explanationAnswer & explanation
Correct answer: D. 9
According to NEC Annex C, Table C.1 (EMT), a 1/2-inch EMT conduit can accommodate a maximum of nine 14 AWG THHN conductors.
Why the other options are wrong
- A. 12 conductors is significantly over the limit for 14 AWG THHN in 1/2-inch EMT.
- B. 7 conductors is below the maximum allowed for 14 AWG THHN in 1/2-inch EMT.
- C. 10 conductors would exceed the allowable fill for 14 AWG THHN in 1/2-inch EMT.
Conduit Fill for EMT
The maximum number of conductors allowed in Electrical Metallic Tubing (EMT) based on conductor size, insulation type, and conduit trade size, specified in NEC Annex C.
- NEC Annex C tables provide pre-calculated maximum conductor counts for various conduit types.
- These tables simplify conduit fill calculations, replacing the need for individual area calculations.
- Always ensure the conductor insulation type (e.g., THHN, THWN) matches the table used.
Memory trick: EMT fill: 'Easy' 'Measurement' 'Table' for 'Conductor' 'Counts'.