Question 1

When determining the number of conductors in a conduit, which Chapter 9 Table is used for the dimensions of the conductors?

Accepted Answer

Chapter 9 Table 5 gives the specific dimensions (area) of insulated conductors (THHN, XHHW, etc.). Table 4 is for Conduit dimensions. Table 1 is percentages.

Question 2

What is the maximum fill percentage for a conduit containing only one conductor?

Accepted Answer

Chapter 9 Table 1 allows 53% fill for 1 conductor.

Question 3

When calculating conduit fill for three or more conductors, the maximum permitted fill is:

Accepted Answer

Chapter 9 Table 1 allows 40% fill for over 2 conductors.

Question 4

A conduit nipple (24 inches or less) can be filled to a maximum of:

Accepted Answer

Chapter 9 Table 1 Note 4 permits nipples not exceeding 24 inches to be filled to 60%.

Question 5

When three conductors of the same size and insulation are installed in a conduit, you should refer to:

Accepted Answer

Annex C provides pre-calculated lookup tables for the maximum number of conductors of the same size and type in various conduits (based on the 40% rule).

Question 6

The 'Jam Ratio' warning applies when determining the number of conductors for:

Accepted Answer

Chapter 9 Table 1 FPN No. 2 warns about the jam ratio when installing THREE conductors. If the ratio of conduit ID to conductor OD is between 2.8 and 3.2, jamming can occur.

Question 7

When calculating fill for a combination of different conductor sizes, you must use:

Accepted Answer

For mixed wire sizes, you must calculate the total area using the specific conductor areas from Table 5 and compare it to the allowable area (40%) of the conduit from Table 4.

Question 8

Equipment grounding conductors are:

Accepted Answer

Chapter 9 Note 3 states that equipment grounding or bonding conductors, where installed, shall be included when calculating conduit fill.

Question 9

In a wireway, the maximum fill for conductors (sum of cross-sectional areas) is:

Accepted Answer

NEC 376.22(A) limits the sum of cross-sectional areas of all contained conductors in a wireway to 20% of the interior cross-sectional area of the wireway.

Question 10

If a multiconductor cable (like a fiber optic cable or tray cable) is installed in a conduit, how is its fill calculated?

Accepted Answer

NEC Chapter 9, Note 9 states that a multiconductor cable, optical fiber cable, or flexible cord shall be treated as a single conductor when calculating conduit fill percentage. The cross-sectional area of the entire cable assembly is used as the area for that single entry in the fill calculation, compared against the applicable fill percentage from Table 1.

Question 11

For the purpose of conduit fill, Compact Stranded conductors:

Accepted Answer

Chapter 9 Table 5A provides specific dimensions for Compact Stranded aluminum and copper conductors, which are smaller than standard concentric stranded conductors.

Question 12

When conductors are installed in surface metal raceways (Wiremold), if the raceway is used for splices (like a wireway), the fill must not exceed 20%. If it contains only conductors (no splices), the fill is:

Accepted Answer

NEC 386.22 invokes the standard conduit fill tables (40% for >2 conductors) unless the specific manufacturer listing says otherwise, but usually surface raceways follow standard fill or specific capacity tables provided by manufacturer. However, NEC 386.22 says 'shall not exceed the number... permitted in Table 1 of Chapter 9', which is 40%.

Question 13

Which conduit type generally has the largest internal diameter (and thus most fill capacity) for the same trade size?

Accepted Answer

EMT (thin wall) typically has a larger ID than Schedule 40 or 80 PVC (which have thicker walls). RMC is also thick. EMT is usually the 'roomiest' for fill among rigid types. (Comparing Table 4 data: 1 inch EMT Area = 0.864 sq in. 1 inch Sch 40 PVC = 0.829. 1 inch Sch 80 = 0.716).

Question 14

When conduit fill calculations result in a decimal of 0.8 or larger, you may:

Accepted Answer

Chapter 9 Note 7 states that when the calculation results in a decimal of 0.8 or larger, it may be rounded to the next higher whole number.

Question 15

For a conduit containing 2 conductors, the maximum fill is:

Accepted Answer

Chapter 9 Table 1 limits fill for exactly 2 conductors to 31%.

Question 16

When calculating the number of conductors allowed in a conduit, if the conductors are all the same size (e.g., all 12 AWG THHN), is it permitted to use the Annex C tables instead of calculating area?

Accepted Answer

Annex C is specifically provided for the common condition where all conductors in a raceway are of the same size and insulation type, allowing a direct lookup without manual calculation.

Question 17

The maximum fill for a Cellular Metal Floor Raceway containing splices at a junction box is:

Accepted Answer

NEC 374.56 states that conductors shall not fill the cellular metal floor raceway to more than 40% of the cross-sectional area, EXCEPT at junction boxes/splices where it is permitted to be filled to 75%.

Question 18

Which table should be used to find the actual cross-sectional area of a specific trade size of Electrical Metallic Tubing (EMT)?

Accepted Answer

Chapter 9 Table 4 lists the dimensions and allowable fill areas for all raceway types (EMT, RMC, PVC, etc.).

Question 19

When installing conductors in a short section of conduit used to protect cables from physical damage (sleeve), the conduit fill is permitted to be:

Accepted Answer

Chapter 9 Table 1 Note 2 states that the table does not apply to short sections of conduit used to protect exposed wiring from physical damage (sleeves). Use is limited only by practicability (ability to pull without damage).

Question 20

Determine the maximum number of 12 AWG THHN conductors permitted in 1/2 inch EMT.

Accepted Answer

Using Annex C, Table C.1 (EMT): For 1/2 inch EMT, 12 AWG THHN, the max number is 9.

Question 21

For Flexible Metal Conduit (FMC) containing 3 or more conductors, the maximum fill is:

Accepted Answer

FMC follows the standard Table 1 percentages: 40% for over 2 conductors.

Question 22

Strut-type channel raceways can be filled to _____ if they contain joiners but no splices.

Accepted Answer

NEC 384.22 allows 40% fill for strut-type channel raceways (standard raceway fill).

Question 23

When a conduit contains only lead-covered conductors, the maximum fill is:

Accepted Answer

Older editions of NEC Chapter 9 Table 1 specified a reduced fill percentage of 38% for conduits containing lead-covered conductors, to account for the additional bulk and rigidity of the lead sheathing. While modern NEC editions have streamlined Table 1 to use standard percentages, this 38% value remains the historically tested reference for lead-covered conductor fill calculations on many licensing exams.

Question 24

What is the area (sq in) of a 10 AWG THHN conductor?

Accepted Answer

Per NEC Chapter 9, Table 5, the cross-sectional area of a 10 AWG THHN/THWN conductor is 0.0211 square inches. This value is used when calculating conduit fill percentages. Table 5 is the standard reference for conductor areas in fill calculations for all commonly used conductor types and sizes.

Question 25

The cross-sectional area of a Scheduled 80 PVC conduit is _____ than that of a Schedule 40 PVC conduit of the same trade size.

Accepted Answer

Schedule 80 has a thicker wall for physical protection, which reduces the internal cross-sectional area available for conductors.

Question 26

When pulling three conductors into a raceway, if the ratio of the raceway diameter to the conductor diameter is approx 3.0, what problem may occur?

Accepted Answer

This is the 'Jam Ratio' (FPN No 2 to Table 1). Conductors can align in a triangular formation and jam against the walls.

Question 27

Underfloor raceways (Article 390) combined with cables: The combined cross-sectional area of all conductors and cables shall not exceed:

Accepted Answer

NEC 390.22 states that the combined cross-sectional area of all conductors or cables shall not exceed 40% of the interior cross-sectional area of the raceway.

Question 28

For a 24-inch nipple, fill is allowed up to 60%. If the nipple is 25 inches long, the maximum fill is:

Accepted Answer

Once the conduit exceeds 24 inches, it is no longer a nipple under Note 4, and standard Table 1 rules apply (40% for 3+ wires).

Question 29

Liquidtight Flexible Metal Conduit (LFMC) of 3/8 inch trade size is permitted for:

Accepted Answer

NEC 350.20 (size) generally starts at 1/2 inch, but 350.20(A) Exception permits 3/8 inch for specific uses like enclosed leads of motors or luminaire whips (fixture tails) not exceeding 6 feet.

Question 30

When conductors are installed in an auxiliary gutter, the sum of the cross-sectional areas of all contained conductors shall not exceed _____ of the interior cross-sectional area.

Accepted Answer

NEC 366.22(A) limits the fill of sheet metal auxiliary gutters to 20%.

Question 31

For calculating fill, if a bare conductor is present, you should use:

Accepted Answer

Chapter 9 Note 8 states that for bare conductors, the dimensions in Table 8 shall be used.

Question 32

Per NEC Chapter 9, Table 1, what is the maximum conduit fill for a raceway containing more than two conductors?

Accepted Answer

Chapter 9, Table 1 sets fill limits of 53% for one conductor, 31% for two, and 40% for more than two conductors.

Question 33

How many 12 AWG THHN conductors may be installed in 1/2-inch EMT?

Accepted Answer

1/2-inch EMT has 0.304 sq in of area; 40% is 0.1216 sq in. A 12 AWG THHN conductor is 0.0133 sq in, so 0.1216 / 0.0133 = 9.1, rounded down to 9 (confirmed by Annex C, Table C.1).

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