CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A commercial kitchen requires a new 208V, 3-phase, 50A circuit for a combination oven. The circuit will be run in EMT conduit. The plans specify using three 6 AWG THHN copper conductors and one 10 AWG THHN copper equipment grounding conductor. What is the minimum trade size of EMT conduit required for this installation?
- A1 1/2 inch
- B1 1/4 inch
- C3/4 inch
- D1 inch
Show answer & explanationAnswer & explanation
Correct answer: D. 1 inch
To accommodate three 6 AWG THHN copper conductors and one 10 AWG THHN copper equipment grounding conductor, a minimum of 1-inch EMT conduit is required based on NEC Chapter 9, Table 4 and Annex C.
Why the other options are wrong
- A. 1 1/2 inch EMT is significantly oversized for this conductor combination.
- B. 1 1/4 inch EMT is oversized and would increase material and installation costs unnecessarily.
- C. 3/4 inch EMT is too small for these conductors, exceeding the allowable fill capacity.
Conduit Fill Calculation
The process of determining the maximum number of conductors allowed within a conduit based on their cross-sectional area and the conduit's internal volume, as per NEC Chapter 9.
- NEC Table 1, Chapter 9, specifies maximum fill percentages (e.g., 40% for 3+ conductors).
- Conductor areas are found in NEC Chapter 9, Table 5.
- Conduit internal areas are found in NEC Chapter 9, Table 4 or Annex C for specific conduit types.
Memory trick: EMT: 'E'asy 'M'easure 'T'o fit 'C'onductors 'O'r 'N'ot 'D'espite 'U'sing 'I'nside 'T'ables.