TN LLE Raceway and Box Fill 2 — Questions and Answers
Question 1: Per NEC Chapter 9, Table 1, what is the maximum conduit fill percentage for one conductor installed in a raceway?
- 31%
- 40%
- 53% (Correct answer)
- 60%
Correct answer: 53%
NEC Chapter 9, Table 1 permits 53% conduit fill when only one conductor is installed in a raceway.
NEC Chapter 9, Table 1 establishes three fill percentages: 1 conductor = 53%, 2 conductors = 31%, and 3 or more conductors = 40%. The higher percentage for one conductor reflects the easier installation (no jamming) and better heat dissipation. The lower 31% for two conductors accounts for the tendency of two round conductors to jam in a conduit.
Question 2: What is the minimum depth of a 4-inch square metal box commonly used at junction points?
- 1-1/4 inches
- 1-1/2 inches
- 2-1/8 inches (Correct answer)
- 1-5/8 inches
Correct answer: 2-1/8 inches
A standard 4-inch square (4S) box commonly used at junction points is 2-1/8 inches deep, providing 30.3 cubic inches of volume.
Standard 4-inch square (4S) metal boxes come in several depths: 1-1/4 inch deep (21.0 cubic inches), 1-1/2 inch deep (25.5 cubic inches), and 2-1/8 inch deep (30.3 cubic inches). The 2-1/8 inch depth is most commonly used at junction points because it provides the most volume for conductor and device fill calculations per NEC 314.16.
Question 3: Per NEC 314.28(A)(1), what is the minimum length of a pull box for a straight pull with 2-inch conduit?
- 6 inches
- 12 inches
- 16 inches (Correct answer)
- 24 inches
Correct answer: 16 inches
For a straight pull, NEC 314.28(A)(1) requires the box length to be at least 8 times the trade size of the largest raceway. 8 x 2 = 16 inches.
NEC 314.28(A)(1) requires pull boxes for straight pulls to have a length not less than 8 times the trade size of the largest raceway. For a 2-inch conduit: 8 x 2 = 16 inches minimum. For angle pulls, NEC 314.28(A)(2) uses a different formula: 6 times the trade size of the largest raceway plus the sum of the trade sizes of all other raceways on the same wall.
Question 4: Per NEC 314.16(B)(5), how many volume allowances does a single-gang yoke or strap with a device (switch or receptacle) count as?
- One volume allowance
- Two volume allowances (Correct answer)
- Three volume allowances
- No volume allowance
Correct answer: Two volume allowances
NEC 314.16(B)(5) counts each device or yoke/strap as two volume allowances of the largest conductor connected to the device.
NEC 314.16(B)(5) requires that for each device or equipment yoke/strap on a single-gang mounting, two volume allowances be included based on the largest conductor connected to the device or equipment. For a standard single receptacle or switch with 14 AWG wiring: 2 x 2.0 cubic inches = 4.0 cubic inches.
Question 5: What is the maximum number of quarter bends (90 degrees) permitted between pull points in a conduit run per NEC 344.26?
- Two (180 degrees total)
- Three (270 degrees total)
- Four (360 degrees total) (Correct answer)
- No limit if conduit is properly supported
Correct answer: Four (360 degrees total)
NEC 344.26 limits bends between pull points to a total of 360 degrees, equivalent to four quarter bends.
NEC 344.26 (RMC), 358.26 (EMT), 342.26 (IMC), and similar sections limit the total number of bends between pull points to not more than 360 degrees (four quarter bends). This limit exists because each bend increases friction during conductor pulling, and exceeding 360 degrees makes pulling extremely difficult and risks conductor insulation damage.
Question 6: Per NEC 314.16(B)(1), how is a conductor counted for box fill if it passes straight through a box without splice or termination?
- It is not counted
- It counts as one conductor volume (Correct answer)
- It counts as two conductor volumes
- It counts as half a conductor volume
Correct answer: It counts as one conductor volume
NEC 314.16(B)(1) states that each conductor that passes through a box without splice or termination counts as one volume allowance.
NEC 314.16(B)(1) conductor counting rules: Each conductor that originates outside the box and terminates or is spliced within the box counts as one volume allowance. A conductor that passes through without splice or termination also counts as one volume allowance. A conductor with no part leaving the box (pigtail) is not counted.
TN LLE Raceway and Box Fill 2
Per NEC Chapter 9, Table 1, what is the maximum conduit fill percentage for one conductor installed in a raceway?