Box Fill Practice Questions (NEC 314.16)
These 29 original, unofficial box fill practice questions cover core 14, 12 and 10 AWG calculations using 2026 NEC-based guidance. Use the edition named by your exam, and open each explanation after choosing an answer.
Question 1 of 29
A duplex receptacle has two outlets on one mounting strap (yoke). Every conductor connected to it is 12 AWG. What volume does the receptacle itself require? Use 2.25 in³ per 12 AWG allowance.
- A. 2.25 in³
- B. 4.50 in³
- C. 6.75 in³
- D. 9.00 in³
Reveal answer and explanation
Answer: B. 4.50 in³
Work: 1 yoke × 2 allowances × 2.25 in³ = 4.50 in³
Why: Devices are counted per yoke, not per outlet. One yoke gets a double allowance based on the largest conductor connected to it.
The other choices: A counts the yoke once. D treats the two outlets as two yokes. C has no basis in the rule.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 2 of 29
Four 14 AWG ungrounded (hot) conductors and four 14 AWG neutrals enter a junction box and are spliced there. What volume do these eight insulated conductors require? Ignore everything else in the box.
- A. 8.00 in³
- B. 10.00 in³
- C. 12.00 in³
- D. 16.00 in³
Reveal answer and explanation
Answer: D. 16.00 in³
Work: (4 + 4) × 2.00 in³ = 16.00 in³
Why: Every insulated conductor that enters and is spliced or terminated counts once, neutrals included. Box fill is about physical space, not which conductors carry current.
The other choices: A drops the neutrals. B lumps the four neutrals into one allowance, which is a grounding-conductor rule, not a neutral rule. C counts six conductors instead of eight.
Source: Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 3 of 29
Two 14/3 cables with ground and one 14/2 cable with ground enter a box, and all conductors are spliced or terminated. How many conductors go into the insulated-conductor count?
- A. 3
- B. 6
- C. 8
- D. 11
Reveal answer and explanation
Answer: C. 8
Work: 3 + 3 + 2 = 8 insulated conductors. The three grounds are counted separately under the grounding rule.
Why: Count the insulated conductors inside each cable, not the cables. “14/3 with ground” means three insulated conductors plus a ground.
The other choices: A counts cables. B treats every cable as two-wire. D adds the grounds into the insulated count, where they don’t belong.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation
Question 4 of 29
Four 14 AWG, three 12 AWG and two 10 AWG insulated conductors enter and terminate in a box. What is the insulated-conductor subtotal only? Use 2.00, 2.25 and 2.50 in³ per allowance, respectively.
- A. 19.75 in³
- B. 18.00 in³
- C. 22.50 in³
- D. 20.25 in³
Reveal answer and explanation
Answer: A. 19.75 in³
Work: (4 × 2.00) + (3 × 2.25) + (2 × 2.50) = 8.00 + 6.75 + 5.00 = 19.75 in³
Why: Multiply each wire-size group by its own allowance, then add the subtotals. Do not assign the largest conductor’s allowance to every insulated wire.
The other choices: B uses the 14 AWG allowance for all nine conductors. C uses the 10 AWG allowance for all nine. D uses the 12 AWG allowance for all nine.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 5 of 29
A problem says that 12 AWG equipment grounding conductors enter a box, but it does not say how many. All other conductors are also 12 AWG, and no other grounding arrangement is involved. Which additional fact is needed to calculate the grounding-conductor allowance?
- A. The number of entering equipment grounding conductors.
- B. The number of neutral conductors.
- C. The marked box volume.
- D. The number of device yokes.
Reveal answer and explanation
Answer: A. The number of entering equipment grounding conductors.
Work: One through four entering grounds require one allowance. A fifth ground adds another ¼ allowance, so an unspecified count does not determine a single grounding volume.
Why: You need the entering-ground count before deciding whether the extra-quarter rule applies. Knowing the gauge alone is not enough.
The other choices: B belongs to the insulated-conductor inventory. C is used later to compare available volume with required volume. D determines device fill, not the entering-ground count.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 6 of 29
A box has three field-installed internal cable clamps, and each clamp holds a 14/2 cable. A 10 AWG conductor also enters the box through a raceway (no clamp). No conductor is larger than 10 AWG. What is the total clamp allowance?
- A. 2.00 in³
- B. 2.50 in³
- C. 6.00 in³
- D. 7.50 in³
Reveal answer and explanation
Answer: B. 2.50 in³
Work: All internal clamps together = 1 allowance, sized by the largest conductor in the box (10 AWG) = 2.50 in³
Why: Clamps get one allowance total, no matter how many there are, and it’s based on the largest conductor anywhere in the box, not the cable in the clamp.
The other choices: A sizes the allowance by the clamped cable. C and D count each clamp separately.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 7 of 29
A 2-gang box holds two single-pole switches on separate yokes. Switch 1 is connected only to 12 AWG conductors. Switch 2 is connected only to 14 AWG conductors. What is the total device allowance?
- A. 4.25 in³
- B. 8.00 in³
- C. 8.50 in³
- D. 9.00 in³
Reveal answer and explanation
Answer: C. 8.50 in³
Work: Switch 1: 2 × 2.25 = 4.50. Switch 2: 2 × 2.00 = 4.00. Total 8.50 in³.
Why: Each yoke is sized by the largest conductor connected to that device, not the largest conductor in the box. That’s the opposite of the clamp rule.
The other choices: A counts each yoke once. B uses 14 AWG for both. D uses 12 AWG for both.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation
Question 8 of 29
One ordinary receptacle occupies a single-gang yoke. Its connected conductors, including its grounding connection, are 12 AWG or 14 AWG, with at least one 12 AWG connection. A separate 10 AWG conductor is spliced in the same box but is not connected to the receptacle. What volume does the receptacle itself require?
- A. 4.50 in³
- B. 4.00 in³
- C. 5.00 in³
- D. 2.25 in³
Reveal answer and explanation
Answer: A. 4.50 in³
Work: Largest conductor connected to this yoke: 12 AWG. Device fill = 2 × 2.25 = 4.50 in³.
Why: Use the largest conductor connected to the device, not the largest conductor anywhere in the box. The unrelated 10 AWG conductor has its own conductor allowance but does not set this yoke’s allowance.
The other choices: B uses the smaller connected wire. C incorrectly uses the unrelated 10 AWG conductor. D counts the yoke only once.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation
Question 9 of 29
In a volume-only comparison, a single-yoke switch connected only to 14 AWG conductors is removed. The entering-conductor inventory, grounding group, clamps and every other fill allowance remain unchanged. By how much does the required volume decrease?
- A. 0 in³
- B. 2.00 in³
- C. 4.00 in³
- D. 8.00 in³
Reveal answer and explanation
Answer: C. 4.00 in³
Work: Removed switch: 2 × 2.00 = 4.00 in³. All other category totals stay the same.
Why: Subtract the switch’s two allowances, not the conductors that were connected to it. The question explicitly keeps the entering-conductor inventory unchanged.
The other choices: A ignores the removed device allowance. B subtracts only one allowance. D subtracts four allowances rather than two.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 10 of 29
Three equipment grounding conductors enter a box: one 14 AWG, one 12 AWG and one 10 AWG. No other equipment grounding conductors or equipment bonding jumpers enter. What is the combined grounding allowance?
- A. 2.00 in³
- B. 2.25 in³
- C. 2.50 in³
- D. 6.75 in³
Reveal answer and explanation
Answer: C. 2.50 in³
Work: Up to four EGCs = 1 allowance at the largest EGC (10 AWG) = 2.50 in³
Why: Up to four equipment grounding conductors share one allowance, sized by the largest of them.
The other choices: A and B use a smaller ground. D adds all three as if each needed its own allowance.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 11 of 29
A metal device box marked 14.0 in³ contains two 14/2 cables with ground and a single-pole switch on one yoke. All conductors enter and are spliced or terminated; every switch connection is 14 AWG. There are no internal clamps or other fill allowances. Does the marked volume meet the calculated requirement?
- A. Yes. 14.0 in³ is required.
- B. No. 16.0 in³ is required.
- C. Yes. 12.0 in³ is required.
- D. No. 18.0 in³ is required.
Reveal answer and explanation
Answer: A. Yes. 14.0 in³ is required.
Work: Insulated conductors 4 + grounds 1 + switch 2 = 7 × 2.00 = 14.0 in³. The box holds 14.0 in³.
Why: The contents must not exceed the box volume, so an exact match meets this volume requirement. People often reject an exact match on instinct. This does not establish compliance with every installation requirement.
The other choices: B counts the two grounds separately. C forgets the switch’s second allowance. D adds a clamp and counts the grounds separately.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 12 of 29
A box marked 21.0 in³ has field-installed internal cable clamps. It contains one 12/3 cable with ground, one 12/2 cable with ground, and a receptacle on one yoke connected only to 12 AWG. All conductors enter and are spliced or terminated. No other fill allowances apply. What volume is required?
- A. 18.00 in³
- B. 20.25 in³
- C. 22.50 in³
- D. 24.75 in³
Reveal answer and explanation
Answer: B. 20.25 in³
Work: Insulated 3 + 2 = 5; grounds 1; receptacle 2; clamps 1 → 9 × 2.25 = 20.25 in³ (fits in 21.0)
Why: Both cables’ grounds share one allowance. Count them separately and you get a false fail.
The other choices: A leaves out the clamps. C counts the two grounds separately. D counts the grounds separately and doubles the clamp allowance.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 13 of 29
A box contains two 12 AWG insulated conductors spliced together, four 14 AWG insulated conductors, a single-pole switch on one yoke connected only to 14 AWG, field-installed internal clamps, and four equipment grounding conductors (the largest is 12 AWG). All conductors enter and are spliced or terminated. No other fill allowances apply. What volume is required?
- A. 18.75 in³
- B. 20.75 in³
- C. 21.00 in³
- D. 21.50 in³
Reveal answer and explanation
Answer: C. 21.00 in³
Work: 12 AWG: 2 × 2.25 = 4.50 · 14 AWG: 4 × 2.00 = 8.00 · clamps (largest in box, 12) = 2.25 · switch (largest connected, 14) = 2 × 2.00 = 4.00 · grounds (largest ground, 12) = 2.25 · total 21.00 in³
Why: This one tests all three “largest” rules: clamps use the largest conductor in the box, a device uses the largest conductor on its yoke, grounds use the largest ground.
The other choices: A leaves out the clamps. B sizes the clamps by 14 AWG instead of the largest conductor in the box. D sizes the switch by 12 AWG, a conductor that isn’t connected to it.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 14 of 29
For an insulated-conductor subtotal, two entering 12 AWG conductors are replaced by two entering 10 AWG conductors. Both pairs terminate in the box, and the number of conductors stays the same. By how much does this insulated-conductor subtotal increase? Use 2.25 in³ for 12 AWG and 2.50 in³ for 10 AWG.
- A. 0 in³
- B. 0.25 in³
- C. 2.50 in³
- D. 0.50 in³
Reveal answer and explanation
Answer: D. 0.50 in³
Work: Before: 2 × 2.25 = 4.50 in³. After: 2 × 2.50 = 5.00 in³. Increase: 5.00 − 4.50 = 0.50 in³.
Why: The count stays at two, but each conductor now has a larger volume allowance. This question asks only for the change in the insulated-conductor subtotal.
The other choices: A ignores the size change. B calculates the increase for just one conductor. C gives one new conductor’s entire allowance, not the increase for the pair.
Source: Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 15 of 29
An ordinary device on one single-gang yoke requires a total device allowance of 5.00 in³. The largest conductor connected to it is either 14, 12 or 10 AWG. Which size is it? The respective per-conductor allowances are 2.00, 2.25 and 2.50 in³.
- A. 14 AWG
- B. 12 AWG
- C. 10 AWG
- D. Any of those three sizes.
Reveal answer and explanation
Answer: C. 10 AWG
Work: 5.00 ÷ 2 = 2.50 in³ per allowance, which corresponds to 10 AWG.
Why: A single-gang yoke uses two allowances. Divide the stated device volume by two before matching the conductor size.
The other choices: A would give 4.00 in³ for the yoke. B would give 4.50 in³. D ignores the different volumes assigned to the three stated sizes.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 16 of 29
A box will hold two 14/2 cables with ground, field-installed internal cable clamps, and one receptacle on one yoke connected only to 14 AWG. All conductors enter and are spliced or terminated, and no other fill allowances apply. Which is the smallest of these marked box volumes that meets the requirement?
- A. 12.5 in³
- B. 15.5 in³
- C. 21.5 in³
- D. 30.3 in³
Reveal answer and explanation
Answer: C. 21.5 in³
Work: Insulated 4 + grounds 1 + clamps 1 + receptacle 2 = 8 × 2.00 = 16.0 in³. 15.5 in³ is too small; 21.5 in³ works.
Why: Compare the complete required volume with each offered capacity. The smallest adequate choice need not equal the calculated requirement.
The other choices: B is short by 0.5 in³; omitting the clamp allowance would wrongly make it appear sufficient. A is also too small. D works but is not the smallest listed.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 17 of 29
Six 12 AWG equipment grounding conductors enter a box. All conductors in this box are 12 AWG, and no other equipment grounding conductors or equipment bonding jumpers enter. What is the total grounding allowance?
- A. 2.25 in³
- B. 2.8125 in³
- C. 3.375 in³
- D. 13.50 in³
Reveal answer and explanation
Answer: C. 3.375 in³
Work: First 4 = 1 allowance; 2 more × ¼ = ½ allowance; 1.5 × 2.25 = 3.375 in³
Why: The cited 2026 NEC-based guidance assigns one allowance to the first four grounds and a quarter allowance to each additional ground. Here every relevant conductor is 12 AWG, so each allowance uses 2.25 in³.
The other choices: A omits both additional quarter allowances. B adds only one quarter. D counts every ground fully.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 18 of 29
A nonmetallic box marked 22.0 in³ holds four 14/2 cables with ground, with no devices, internal clamps or other fill allowances. A fifth identical cable is added. All conductors enter and are spliced, and nothing else changes. Does the box still have enough volume?
- A. Yes. 20.00 in³ is required.
- B. Yes. 22.00 in³ is required.
- C. No. 22.50 in³ is required.
- D. No. 30.00 in³ is required.
Reveal answer and explanation
Answer: C. No. 22.50 in³ is required.
Work: Insulated 10 × 2.00 = 20.00. Grounds: 5 → 1¼ allowances × 2.00 = 2.50. Total 22.50 in³ > 22.0 in³.
Why: The new cable adds two insulated conductors and pushes the ground count past four, so the ground allowance grows too. Recalculate every category a change touches. (Before the change: 8 × 2.00 + 2.00 = 18.00 in³.)
The other choices: A leaves out the grounds. B updates the conductors but not the grounds. D counts all five grounds fully.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 19 of 29
Fourteen 12 AWG insulated conductors and seven 12 AWG equipment grounding conductors enter a box and terminate there. There are no devices, internal clamps or other fill allowances. What is the exact required volume?
- A. 33.75 in³
- B. 35.4375 in³
- C. 36.00 in³
- D. 47.25 in³
Reveal answer and explanation
Answer: B. 35.4375 in³
Work: Insulated 14 × 2.25 = 31.50. Grounds: 1 + (3 × ¼) = 1.75 allowances × 2.25 = 3.9375. Total 35.4375 in³.
Why: Keep the fraction until you compare with the box. A box marked 35.4 in³ would be too small, even though 35.4375 “rounds” to 35.4.
The other choices: A omits the three additional quarter allowances. C counts the three extra grounds as one full allowance. D counts every ground fully.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 20 of 29
A box has field-installed internal cable clamps, and its largest conductor is initially 12 AWG. Two 10 AWG insulated conductors are added through a raceway and spliced in the box. They do not connect to a device. The grounding inventory and every allowance other than insulated conductors and clamps stay unchanged. How much does the total required volume increase?
- A. 5.00 in³
- B. 2.75 in³
- C. 5.25 in³
- D. 7.50 in³
Reveal answer and explanation
Answer: C. 5.25 in³
Work: Added conductors: 2 × 2.50 = 5.00 in³. Clamp increase: 2.50 − 2.25 = 0.25 in³. Total increase: 5.00 + 0.25 = 5.25 in³.
Why: Recalculate every category the added conductors affect. The clamp group still gets one allowance, but its controlling conductor size changes from 12 AWG to 10 AWG.
The other choices: A misses the change in clamp size. B adds only one of the two new conductors. D adds a whole new clamp allowance instead of replacing the old 2.25 in³ allowance with 2.50 in³.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 21 of 29
Three 10 AWG insulated conductors and one 12 AWG equipment grounding conductor enter a box and are spliced or terminated there. There are no devices, internal clamps or other fill allowances. What volume is required?
- A. 9.00 in³
- B. 7.50 in³
- C. 9.75 in³
- D. 10.00 in³
Reveal answer and explanation
Answer: C. 9.75 in³
Work: Insulated conductors: 3 × 2.50 = 7.50 in³. Ground: 1 × 2.25 = 2.25 in³. Total: 9.75 in³.
Why: The grounding allowance is sized by the entering ground, not the larger insulated conductors. Keep those categories separate.
The other choices: A uses the 12 AWG allowance for all four conductors. B leaves out the ground. D incorrectly sizes the ground allowance at 10 AWG.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 22 of 29
A box marked 30.3 in³ contains four 12 AWG insulated conductors, two 12 AWG equipment grounding conductors, and a receptacle on one yoke connected only to 12 AWG. All conductors enter and are spliced or terminated. There are no clamps or other fill allowances. How many more 14 AWG insulated conductors can enter and terminate in the box if no grounds are added and every other allowance stays unchanged?
- A. 6
- B. 7
- C. 8
- D. 15
Reveal answer and explanation
Answer: B. 7
Work: Used: (4 + 1 + 2) × 2.25 = 15.75. Left: 30.3 − 15.75 = 14.55. 14.55 ÷ 2.00 = 7.275 → 7.
Why: Round down. Part of a conductor doesn’t fit.
The other choices: C rounds 7.275 up. A leaves unused space for no reason. D divides the whole box by 2.00 and ignores what’s already in it.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 23 of 29
A single-gang nonmetallic box is marked 22.5 in³. It holds three 14/2 cables with ground and a switch on one yoke connected only to 14 AWG. All conductors enter and are spliced or terminated. There are no internal clamps or other fill allowances. How many more 14 AWG insulated conductors can enter and terminate if no grounds are added and every other allowance stays unchanged?
- A. 1
- B. 2
- C. 3
- D. 4
Reveal answer and explanation
Answer: B. 2
Work: Insulated 6 + grounds 1 + switch 2 = 9 × 2.00 = 18.0. Left: 22.5 − 18.0 = 4.5. 4.5 ÷ 2.00 = 2.25 → 2.
Why: Use the volume marked on the nonmetallic box. Subtract the existing fill before dividing the remaining volume by the new conductor’s allowance.
The other choices: C rounds up. A undercounts the space. D ignores the switch.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 24 of 29
A nonmetallic box is marked 24.5 in³. It holds two 12/2 cables with ground, one 12/3 cable with ground, and a receptacle on one yoke connected only to 12 AWG. All conductors enter and are spliced or terminated; there are no clamps or other fill allowances. A student substitutes a 21.0 in³ value from a metal-box table instead of using the marking. Does the stated box have enough volume?
- A. No. 22.50 in³ is required and only 21.0 in³ is available.
- B. Yes. 22.50 in³ is required and 24.5 in³ is available.
- C. Yes. Only 20.25 in³ is required.
- D. No. 27.00 in³ is required.
Reveal answer and explanation
Answer: B. Yes. 22.50 in³ is required and 24.5 in³ is available.
Work: Insulated 2 + 2 + 3 = 7; grounds 1; receptacle 2 → 10 × 2.25 = 22.50 in³. Available marked volume: 24.5 in³. Spare volume: 2.00 in³.
Why: Use the stated marking for this nonmetallic box. An unrelated metal-box table value does not replace that marking.
The other choices: A substitutes the wrong available volume. C misses one insulated conductor. D counts the three grounds as three full allowances.
Source: Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046 · Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation
Question 25 of 29
For this volume-only exercise, a box has a stated available volume of 42.0 in³. It will contain only entering 12 AWG insulated conductors spliced or terminated in the box, with no other fill allowances. What is the maximum whole number of these conductors?
- A. 16
- B. 18
- C. 19
- D. 21
Reveal answer and explanation
Answer: B. 18
Work: 42.0 ÷ 2.25 = 18⅔ → 18 conductors. Check: 18 × 2.25 = 40.50 in³; 19 × 2.25 = 42.75 in³, which exceeds 42.0 in³.
Why: Divide available volume by the per-conductor allowance only because this exercise has no other fill allowances. Keep the whole-number maximum; do not round it up.
The other choices: C rounds up to a count that needs 42.75 in³. D divides by the 14 AWG allowance. A is two short of what fits.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 26 of 29
A box will hold four 14 AWG and six 12 AWG insulated conductors; four equipment grounding conductors (one 14 AWG, three 12 AWG); field-installed internal clamps; a switch connected only to 14 AWG; and two receptacles, each connected only to 12 AWG. Each device has its own single-gang yoke. All conductors enter and are spliced or terminated, and no other fill allowances apply. Which is the smallest volume listed that meets the requirement?
- A. 38.50 in³
- B. 38.75 in³
- C. 39.00 in³
- D. 42.00 in³
Reveal answer and explanation
Answer: C. 39.00 in³
Work: 14 AWG 4 × 2.00 = 8.00 · 12 AWG 6 × 2.25 = 13.50 · grounds 2.25 · clamps 2.25 · switch 4.00 · receptacles 2 × 4.50 = 9.00 · total 39.00 in³
Why: Keep each wire size in its own subtotal, then apply each “largest” rule to its own category. An exact match is enough for this volume requirement.
The other choices: A and B are just under the requirement. D works but isn’t the smallest listed.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 27 of 29
A complete allowance calculation for a stated box inventory gives 20.25 in³. The box’s available volume is also 20.25 in³. What does that comparison establish by itself?
- A. The conductors have adequate ampacity for the circuit.
- B. Every grounding connection is correctly made.
- C. The box is correctly supported.
- D. The stated box-fill volume requirement is met.
Reveal answer and explanation
Answer: D. The stated box-fill volume requirement is met.
Work: Required volume 20.25 in³ ≤ available volume 20.25 in³. The volume comparison is satisfied exactly.
Why: An exact match satisfies the stated volume calculation. It does not answer separate questions about electrical capacity, connections or mounting.
The other choices: A, B and C each require information that is absent from a box-volume comparison. Matching cubic inches does not establish those facts.
Source: Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046 · Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation
Question 28 of 29
A box has 20.0 in³ of available volume, and all applicable fill allowances total 18.0 in³. A student multiplies the box volume by 40% and compares the required fill with 8.0 in³. Which comparison should be used for this box-fill exercise?
- A. 18.0 in³ required versus 8.0 in³ available.
- B. 18.0 in³ required versus 20.0 in³ available.
- C. 18.0 in³ required versus 12.0 in³ available.
- D. 18 conductors versus a 20-conductor limit.
Reveal answer and explanation
Answer: B. 18.0 in³ required versus 20.0 in³ available.
Work: 18.0 ≤ 20.0, leaving 2.0 in³. The unsupported extra step 20.0 × 0.40 = 8.0 is not part of this calculation.
Why: Add the applicable volume allowances and compare them with the stated available box volume. Do not introduce a percentage reduction that the box-fill problem does not call for.
The other choices: A repeats the student’s error. C uses the remaining 60% instead. D changes volume values into conductor counts without a per-conductor calculation.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Question 29 of 29
A box holds six 14 AWG insulated conductors, three 14 AWG equipment grounding conductors, a switch on one yoke connected only to 14 AWG, and field-installed internal clamps. All conductors enter and are spliced or terminated; no other fill allowances apply. A student writes: insulated 12 in³ + grounds 6 in³ + switch 2 in³ + clamps 0 in³ = 20 in³. Which statement is correct?
- A. The total is right, so the method is right.
- B. The total is right by luck. The correct breakdown is 12 + 2 + 4 + 2 = 20 in³.
- C. Grounds need no volume, so the answer is 18 in³.
- D. The switch counts once, so the answer is 18 in³.
Reveal answer and explanation
Answer: B. The total is right by luck. The correct breakdown is 12 + 2 + 4 + 2 = 20 in³.
Work: Correct: insulated 6 × 2.00 = 12 · grounds 2.00 · switch 4.00 · clamps 2.00 · total 20.00 in³
Why: The student counted grounds 4 in³ too high, the switch 2 in³ too low, and left out 2 in³ of clamps. The errors cancel. Change one detail in the question and they won’t, so check each category, not just the final number.
The other choices: A confuses a matching total with a correct method. C drops the grounds. D undercounts the switch.
Source: Minnesota DLI Electrical License Examination Guide, p. 18, box-fill component calculation · Minnesota DLI 2026 NEC inspection checklist, p. 6, item 046
Review the rule behind a missed answer
Find the rule you missed, then rework those questions without looking at the answers. Write a separate subtotal for each category before you add them up.
| Rule | Questions |
|---|---|
| Insulated conductors, cable notation and separate wire-size subtotals | 2, 3, 4, 14 |
| Recognizing a missing input | 5 |
| Clamps: the largest conductor in the box | 6, 12, 13, 20 |
| Devices: each yoke and its connected conductors | 1, 7, 8, 9, 15 |
| Grounds: the up-to-four group and extra quarter allowances | 10, 17, 18, 19, 21 |
| Complete inventories and the smallest sufficient volume | 11, 12, 13, 16, 26 |
| Marked volumes and how many more conductors fit | 22, 23, 24, 25 |
| Using the volume result without overstating it | 27, 28 |
| Checking your method, not just the total | 29 |
Your results tell you how you did on these questions. They aren't an official score or a prediction of how you'll do on a licensing exam.
Counting rules for this set
Add up the volume allowances for everything in the stated inventory, then compare the total to the box's available volume. An exact match meets the volume requirement; an excess does not.
| What's in the stated inventory | How many allowances | Sized by |
|---|---|---|
| Each insulated conductor that enters and is spliced or terminated | 1 each | Its own size |
| All field-installed internal cable clamps together | 1 total | Largest conductor in the box |
| Each ordinary single-gang device yoke | 2 | Largest conductor connected to that device |
| One through four entering equipment grounding conductors | 1 total | Largest entering equipment grounding conductor |
| Each entering ground beyond four in the same-gauge examples here | An additional ¼ each | The common wire size used in that example |
Sources: Minnesota DLI examination guide, p. 18 and 2026 inspection checklist, p. 6, item 046. These rows describe the ordinary arrangements in the questions, not every Section 314.16 exception or special grounding arrangement.
Volume per allowance for the wire sizes used here:
| Wire size | 14 AWG | 12 AWG | 10 AWG |
|---|---|---|---|
| Cubic inches (in³) | 2.00 | 2.25 | 2.50 |
Source: Minnesota DLI 2026 inspection checklist, p. 6, item 046.
AWG is American Wire Gauge. These are volumes, not wire areas, so don't mix them up with conduit-fill tables.
The box capacities in the questions are supplied exercise values. They are not product recommendations or a substitute for looking up an actual box's permitted volume. For a nonmetallic box, use its marked cubic-inch capacity, as described in DLI's checklist.
How to set up a box fill calculation
- List everything in the box. For the scenarios here, group entering insulated conductors by size, then list entering grounds, internal clamps and each device yoke. Separate a requested subtotal from a complete-box calculation.
- Count and multiply, one category at a time. Conductors use their own size. The internal-clamp group uses the largest conductor in the box. Each device uses the largest conductor connected to it. For the up-to-four ground group, use the largest entering ground; the more-than-four examples here use one gauge throughout.
- Recheck every category affected by a change. A fifth cable can increase both the insulated-conductor subtotal and the grounding allowance. A larger conductor can change the clamp allowance too.
- Compare the total to the box. If the question asks how many more conductors fit, subtract existing fill first, divide what's left by the new conductor's allowance and round down. That shortcut works only when the question keeps other allowances unchanged.
The component allowances come from Minnesota DLI's examination guide, p. 18. Subtracting used volume and keeping only whole conductors are the arithmetic steps needed to stay within the stated capacity.
Write every subtotal down. Question 29 shows why: a right total can hide three wrong counts.
Which NEC edition should you study?
Study the one your exam's candidate bulletin names. That may not be the newest edition, and it may not be the edition your state enforces on job sites. Minnesota DLI's codes and standards page, for example, lists adoption and examination-transition information separately. This set does not establish the assigned edition for another jurisdiction’s examination.
The core 14, 12 and 10 AWG values and the additional-ground note also appear in DLI's 2023 checklist, p. 5. That limited comparison does not establish that every rule, exception or table label is identical across editions.
This is a U.S. NEC-based topic exercise, not a full licensing examination or Canadian Electrical Code practice. Special fittings, canopy exceptions, terminal blocks, conduit bodies and larger-conductor pull-box sizing are outside this set. For those topics, use the complete edition assigned by your examination authority. DLI links to NFPA's official code-access route and states that its free NEC access requires an NFPA account.
Sources and verification
By Castleport Test Prep Editorial Team
Last verified Sept. 29, 2026: the cited core allowances, worked calculations and source links. AI tools assisted the preparation and audit of this material. The calculations were checked with exact arithmetic, and the question text, choices, keys and explanations were checked for consistency. This is a source and calculation check, not a review by a licensed electrician or inspector. The full NFPA code reader was not available in this check; this set is limited to the core calculations supported by the cited state guidance.
- Minnesota DLI, Electrical License Examination Guide: box fill component calculation, p. 18; separate categories and mixed sizes.
- Minnesota DLI, 2026 NEC inspection checklist: box fill table and grounding note, p. 6, item 046.
- Minnesota DLI, 2023 NEC inspection checklist: limited historical comparison of the listed core allowances, p. 5, item 046.
- Minnesota DLI, electrical codes and standards: separate adoption and examination-transition information; NFPA access route.
Read more about our editorial standards.
Castleport Test Prep is an independent exam prep publisher. We're not affiliated with, endorsed by or approved by NFPA, any licensing board or any testing company. These are original, unofficial practice questions, not actual exam items, and they don't approve or direct any electrical work. NEC, National Electrical Code and other names are used only to identify their subjects; trademarks belong to their respective owners.