TN LLE Raceway and Box Fill — 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.
Question 7: Per NEC 358.12, where is EMT (Electrical Metallic Tubing) NOT permitted to be installed?
- In residential walls
- Where subject to severe physical damage, in cinder concrete, and in hazardous locations (with exceptions) (Correct answer)
- In commercial buildings
- Above suspended ceilings
Correct answer: Where subject to severe physical damage, in cinder concrete, and in hazardous locations (with exceptions)
NEC 358.12 prohibits EMT where subject to severe physical damage, embedded in cinder concrete unless protected, and in certain hazardous locations.
NEC 358.12 restricts EMT usage in: (1) Where subject to severe physical damage — EMT walls are thin and can be crushed or dented; (2) Where protected from corrosion solely by enamel; (3) In cinder concrete or cinder fill where subject to permanent moisture unless protected; (4) In hazardous (classified) locations except as permitted by NEC Articles 500-516.
Question 8: Per NEC 314.27(A)(1), what minimum weight must a standard outlet box be listed to support for a ceiling-mounted luminaire?
- 25 pounds
- 35 pounds
- 50 pounds (Correct answer)
- No minimum weight requirement
Correct answer: 50 pounds
NEC 314.27(A)(1) requires that outlet boxes used as the sole support for luminaires must be listed for the weight to be supported, with a minimum of 50 pounds.
NEC 314.27(A)(1) requires that boxes used as the sole support of a luminaire or lampholder must be listed and marked for the maximum weight to be supported, with 50 pounds minimum. For luminaires weighing more than 50 pounds, the box must be specifically listed for the additional weight. Ceiling fan boxes have stricter requirements per 314.27(C).
Question 9: What NEC section provides the volume allowances per conductor based on wire gauge for box fill calculations?
- NEC 314.16(A)
- NEC Table 314.16(B) (Correct answer)
- NEC 310.16
- NEC Chapter 9, Table 5
Correct answer: NEC Table 314.16(B)
NEC Table 314.16(B) provides the volume allowance per conductor for each AWG size used in box fill calculations.
NEC Table 314.16(B) lists conductor volume allowances: 18 AWG = 1.50 cubic inches, 16 AWG = 1.75 cubic inches, 14 AWG = 2.00 cubic inches, 12 AWG = 2.25 cubic inches, 10 AWG = 2.50 cubic inches, 8 AWG = 3.00 cubic inches, 6 AWG = 5.00 cubic inches. These values are used in the box fill calculation per 314.16(B)(1) through (B)(5).
Question 10: Per NEC 314.28(A)(2), what is the minimum distance calculation for an angle pull in a pull box with a 3-inch conduit?
- 18 inches (6 x 3) (Correct answer)
- 24 inches (8 x 3)
- 36 inches
- 12 inches
Correct answer: 18 inches (6 x 3)
For an angle pull, NEC 314.28(A)(2) requires 6 times the trade size of the largest raceway entering that wall. 6 x 3 = 18 inches minimum, plus the sum of other raceways on the same wall.
NEC 314.28(A)(2) angle pull formula: The distance from the raceway entry to the opposite wall must be at least 6 times the trade size of the largest raceway PLUS the sum of all other raceway trade sizes entering the same wall. Example: A pull box with a 3-inch and a 2-inch conduit entering the same wall: 6 x 3 + 2 = 20 inches minimum.
Question 11: Per NEC 312.8, what is the requirement when switches or overcurrent devices are enclosed and conductors enter through the top?
- No specific requirements
- Sufficient wire bending space must be provided, and conductors must not fill the wiring space at any cross-section to more than 40% (Correct answer)
- All conductors must be in separate raceways
- The enclosure must be ventilated
Correct answer: Sufficient wire bending space must be provided, and conductors must not fill the wiring space at any cross-section to more than 40%
NEC 312.8 requires adequate bending space and limits wire fill to prevent overheating and allow safe installation.
NEC 312.8 addresses cabinets, cutout boxes, and meter socket enclosures where conductors enter the enclosure. The wiring space (gutter) at any cross-section must not exceed 40% fill by the conductors — matching the conduit fill rule. Additionally, NEC Table 312.6(A) provides minimum wire bending space based on conductor size.
Question 12: What is the minimum trade size EMT conduit permitted for general wiring per NEC 358.20?
- 1/4 inch
- 3/8 inch
- 1/2 inch (Correct answer)
- 3/4 inch
Correct answer: 1/2 inch
NEC 358.20(A) establishes 1/2-inch (metric designator 16) as the minimum trade size for EMT.
NEC 358.20(A) specifies that EMT smaller than metric designator 16 (trade size 1/2 inch) shall not be used. This minimum size ensures adequate conductor bending radius, structural integrity, and pull ease. For comparison, 3/8-inch flexible metal conduit (FMC) is permitted in certain applications per NEC 348.20(A).
