Boxes and wiring methods

All free sections·Study notes·20-question practice test

1. 1 · Boxes and wiring methods · NEC Knowledge

   The print calls for nonmetallic-sheathed cable on a run that passes through a wet location under a raised house, with the cable lying on the soil. The helper says the cable is fine wherever that product is customary. What should stop the installation?

   1. A. That cable is not a wet-location wiring method, and a cable lying on soil is not a permitted use. Custom is not the article.Keyed answer
   2. B. The cable is permitted in any wet location if the staples are plastic.
   3. C. Soil contact is required for that cable.
   4. D. Wet-location rules apply only to EMT.

   Article 334 limits where nonmetallic-sheathed cable may be used. A wet location and a run lying on the soil are outside those permitted uses. Confirm the uses-not-permitted section in NEC 2026 before you treat a common indoor cable as an underground method.

   Open NEC 2026 Article 334

2. 2 · Boxes and wiring methods · NEC Knowledge

   Nonmetallic-sheathed cable passes through a hole bored close to the face of a wood stud. In plain language, why would you add a steel plate there?

   1. A. So a nail or screw driven into the stud is less likely to hit the cableKeyed answer
   2. B. To use the stud as a grounding electrode
   3. C. To support the cable at 10 ft intervals
   4. D. To raise the ampacity of the cable

   The plate is physical protection against fasteners that miss the stud center. It does not change ampacity and it does not ground the building. The bored-hole rules are in Article 300. Confirm the setback that triggers a plate in NEC 2026.

   Open NEC 2026 Article 300

3. 3 · Boxes and wiring methods · NEC Knowledge

   A run of EMT is meant to be the equipment grounding path, and a set-screw coupling on that run is loose. What is wrong with that, in plain language?

   1. A. The raceway fill percentage goes up
   2. B. The metal path fault current would use is not reliableKeyed answer
   3. C. The conductors inside become continuous loads
   4. D. The raceway becomes a grounding electrode

   A loose coupling breaks the metal path the fault would follow. EMT fittings have to keep that path intact when the raceway is the equipment grounding conductor. Article 358 covers the tubing and fittings. Article 250 is where you confirm that a raceway may serve as the grounding path.

   Open NEC 2026 Article 358

4. 4 · Boxes and wiring methods · NEC Knowledge

   Pigtails that never leave this device box were each given a conductor volume allowance. The helper says every piece of copper in the box counts, including tails that start on the device and end in a wire nut. Which of those tails takes a volume allowance?

   1. A. Every pigtail counts as two allowances because it is connected to a device.
   2. B. Pigtails count only when they are white, and black pigtails are free.
   3. C. None of them. A conductor that originates in the box and does not leave is not a volume allowance. The wires that enter from outside still count.Keyed answer
   4. D. Pigtails replace the entering conductors, so the cables outside the box count as zero.

   Article 314 gives no volume allowance to a conductor that starts inside the box and stays there. Confirm the conductor-count rules in NEC 2026. Do not add a cubic-inch total in this answer.

   Open NEC 2026 Article 314

5. 5 · Boxes and wiring methods · NEC Knowledge

   Two internal cable clamps sit inside the box, and the helper counts two clamp allowances because he sees two clamps. Both clamps are the internal type the fill rule covers. He says each piece of hardware takes its own volume. What does the second clamp add?

   1. A. Nothing beyond the one clamp allowance. One or more internal cable clamps take a single allowance based on the largest conductor, not an allowance per clamp.Keyed answer
   2. B. A second full allowance, because every internal clamp is counted separately.
   3. C. A prohibition on the box, because two clamps make the installation illegal regardless of volume.
   4. D. The same allowance as a device yoke, so the two clamps count as four conductors.

   Article 314 counts internal cable clamps as one volume allowance no matter how many of those clamps are in the box. Confirm the clamp rule in NEC 2026. Do not compute cubic inches here.

   Open NEC 2026 Article 314

6. 6 · Boxes and wiring methods · NEC Knowledge

   A single-gang receptacle yoke was counted as one conductor because the helper says a device takes the same space as the one wire landed on it. The largest conductor on the device is the one he should have used, and he did not double it. What does that yoke count as?

   1. A. One allowance equal to the smallest conductor on the device.
   2. B. Zero, because devices sit outside the box and never enter the fill count.
   3. C. Four allowances for every single-gang receptacle, regardless of the conductors landed on it.
   4. D. Two volume allowances based on the largest conductor connected to the device. One conductor's worth of space is not the yoke.Keyed answer

   Article 314 counts each device yoke as two volume allowances based on the largest conductor connected to that device. Confirm the yoke rule in NEC 2026. This question does not ask for a cubic-inch total.

   Open NEC 2026 Article 314

7. 7 · Boxes and wiring methods · NEC Knowledge

   The helper embedded Type NM cable in the concrete slab and says the concrete protects the cable better than a raceway would. The cable is the ordinary dwelling NM, not a wiring method identified for embedment. What did the slab fail to legalize?

   1. A. A requirement to embed NM in every slab, which he should have extended to the footings too.
   2. B. The embedment. NM cable is not permitted to be embedded in concrete just because the concrete covers it.Keyed answer
   3. C. The equipment ground, because concrete replaces the grounding conductor.
   4. D. Nothing. Concrete is a listed wet-location raceway for NM cable.

   Article 334 does not permit Type NM cable to be embedded in concrete. Covering it is not a wiring method. Confirm the prohibited uses in NEC 2026.

   Open NEC 2026 Article 314

8. 8 · Boxes and wiring methods · NEC Knowledge

   Small Type NM cable is stapled across the underside of the joists in an unfinished basement, perpendicular to the joists. The helper says any NM cable may be fastened to the bottom of a joist because the basement is unfinished and accessible. What size assumption did he skip?

   1. A. That every NM cable, of any size, is required to be stapled to the underside of joists.
   2. B. That unfinished basements prohibit NM cable entirely, so the staples are the violation and the route is irrelevant.
   3. C. That the underside of a joist is a raceway, so box-fill rules size the cable.
   4. D. That not every size may be secured to the underside of joists. This small cable does not get that treatment just because the basement is open.Keyed answer

   Article 334 distinguishes which NM cables may be secured to the underside of joists and which must be bored or run on a running board. Confirm that distinction in NEC 2026. Do not invent the size cutoff in the answer.

   Open NEC 2026 Article 314

9. 9 · Boxes and wiring methods · NEC Knowledge

   The fishing exception is the helper's reason for leaving a new NM run loose and exposed along an open basement wall. Nothing is concealed, and support is easy. He says once any cable may be fished, no NM cable has to be secured. Where does that exception stop?

   1. A. Nowhere. The fishing exception removes every securing rule for NM cable in all buildings.
   2. B. It stops where the cable is not being fished through a concealed space where support is impracticable. An open run he can staple is still secured.Keyed answer
   3. C. At the service point only. Exposed basement cable is required to be unsupported.
   4. D. After the first staple, because one fastener invokes the fishing exception for the rest of the run.

   Article 334 requires NM cable to be secured, and the fishing permission is a narrow case. An exposed basement run is not that case. Confirm the securing rules and the exception in NEC 2026. Do not invent the spacing.

   Open NEC 2026 Article 314

10. 10 · Boxes and wiring methods · NEC Knowledge

    Type NM cable was pulled from the weatherhead to the service disconnect and used as the service-entrance conductors. The helper says NM is allowed on a dwelling, so it is allowed as the service cable too. What use did the dwelling permission fail to include?

    1. A. Nothing. NM cable is the required service-entrance method for a one-family dwelling.
    2. B. Only underground services. Overhead service-entrance conductors are required to be NM.
    3. C. The grounding electrode conductor, which must be NM cable while the service conductors must be bare.
    4. D. Service-entrance conductors. A dwelling permission for NM branch circuits and feeders inside the building is not a service-entrance wiring method.Keyed answer

    Article 334 does not make Type NM cable a service-entrance wiring method just because the building is a dwelling. Confirm the permitted uses in NEC 2026.

    Open NEC 2026 Article 314

11. 11 · Boxes and wiring methods · NEC Knowledge

    Lay-in ceiling support wires are holding the EMT. The helper clipped the raceway to the wires that support the ceiling grid and says metal wire is a listed hanger because it is already in the ceiling. What are those wires actually holding?

    1. A. The raceway by right, because every ceiling wire is a raceway support.
    2. B. Nothing. Ceiling wires are prohibited from holding ceiling tile once conduit is in the room.
    3. C. The ceiling, not the raceway, unless an additional support that the rule allows has actually been installed for the EMT. The grid wires are not automatically that support.Keyed answer
    4. D. The branch-circuit neutral, because a support wire is a grounding conductor.

    Article 300 does not let the EMT use the ceiling-grid support wires as its hanger unless the additional-support permission is actually met. Confirm that permission in NEC 2026.

    Open NEC 2026 Article 314

12. 12 · Boxes and wiring methods · NEC Knowledge

    Aluminum EMT was buried in the earth and the helper says every EMT may be buried because it is a metal raceway. He did not select a steel product identified for earth contact. He treated the metal as interchangeable. What did the word EMT fail to settle?

    1. A. Which EMT may be in contact with the earth. Not every metal used for EMT has the same permission in earth or concrete.Keyed answer
    2. B. That all EMT, including aluminum, is required to be buried rather than installed indoors.
    3. C. That burial is prohibited for every EMT metal, so the steel product would have been illegal too without any confirmation.
    4. D. That the earth is a dry location, so conductor type no longer matters once the EMT is aluminum.

    Article 358 does not give every EMT metal the same permission in the earth. Confirm which product may be in earth contact in NEC 2026 before you bury this aluminum run.

    Open NEC 2026 Article 314

13. 13 · Boxes and wiring methods · NEC Knowledge

    A loose set-screw coupling is the only equipment grounding path on this EMT run, and the helper says the pipe is metal so continuity does not depend on the coupling being tight. No separate equipment grounding conductor was pulled. What does the loose coupling fail to provide?

    1. A. A reason to add a plastic isolation, because EMT is prohibited from being an equipment grounding path under every condition.
    2. B. Nothing. A loose coupling is the required grounding fitting for EMT.
    3. C. The continuous equipment grounding path. EMT may serve as that path only when the installation actually keeps the metal continuous. A loose coupling does not.Keyed answer
    4. D. A neutral connection, because the coupling is required to carry the grounded conductor.

    Article 358 can permit EMT to serve as the equipment grounding conductor only when the fittings maintain continuity. Confirm that condition in NEC 2026. Metal in the room is not the same as a tight coupling.

    Open NEC 2026 Article 314

14. 14 · Boxes and wiring methods · NEC Knowledge

    Wire nuts join the conductors inside the wall cavity, with no box and no other enclosure. The helper says a splice in a concealed cavity is fine if the nuts are tight and the cable is NM. What is missing at the splice?

    1. A. A box or other enclosure the wiring method requires for that splice. A wire nut buried in the wall is not the enclosure.Keyed answer
    2. B. Nothing. Concealed splices are the required method and boxes are only for devices.
    3. C. A second wire nut, because two nuts replace a box.
    4. D. An inline fuse, which is the enclosure for a concealed NM splice.

    Article 300 requires a box or other permitted body where the conductors are spliced. Confirm the box requirement in NEC 2026. Tight wire nuts do not replace it.

    Open NEC 2026 Article 314

15. 15 · Boxes and wiring methods · Calculations

    The problem prints the volume allowance: each 14 AWG conductor counts as 2.00 cubic inches. All equipment grounding conductors together count as one conductor. There is no device and no clamp. The box contains 8 conductors that each count, plus the equipment grounds. What minimum volume do you need?

    1. A. 18.00 cubic inchesKeyed answer
    2. B. 16.00 cubic inches
    3. C. 20.00 cubic inches
    4. D. 10.00 cubic inches

    Eight conductors plus one volume for all the grounds is 9. 9 × 2.00 = 18.00 cubic inches. Leaving the grounds out gives 16.00. On exam day the allowance comes from the box-fill table in Article 314. It is printed here so the count can be practiced.

    Open NEC 2026 Article 314

16. 16 · Boxes and wiring methods · Calculations

    This drill says nonmetallic-sheathed cable is secured at intervals not greater than 4.5 ft. Both ends of this run are already secured at the boxes, and the boxes are 18 ft apart. Counting those two end supports, what is the fewest supports that keep every interval at 4.5 ft or less?

    1. A. 4 supports
    2. B. 5 supportsKeyed answer
    3. C. 6 supports
    4. D. 3 supports

    18 / 4.5 = 4 intervals, which takes 5 supports when both ends are included. Four supports would leave a gap larger than 4.5 ft. Confirm the securing distance for this cable in NEC 2026 Article 334. The 4.5 ft figure is printed in the stem.

    Open NEC 2026 Article 334

17. 17 · Boxes and wiring methods · Calculations

    This drill counts 2.5 cubic inches per volume. There are 4 conductor volumes, 2 for the device, 1 for the equipment grounds, and 1 for the clamps. The box on the shelf is marked 18 cubic inches. How many cubic inches short of the count is that box?

    1. A. 2.00 cubic inchesKeyed answer
    2. B. 10.00 cubic inches
    3. C. 20.00 cubic inches
    4. D. 8.00 cubic inches

    Volumes: 4 + 2 + 1 + 1 = 8. 8 × 2.5 = 20.00 cubic inches. The box is 18, so it is 2.00 cubic inches short. Counting conductors only leaves the device, grounds, and clamps out. Article 314 is box fill. The 2.5 cubic inch figure is printed in the stem.

    Open NEC 2026 Article 314

18. 18 · Boxes and wiring methods · Calculations

    A box contains 2 conductors at 3 cubic inches each and 4 conductors at 2.25 cubic inches each. The device allowance is 2 volumes and the equipment-grounding allowance is 1 volume, both counted at the larger conductor's 2.25 cubic inches. What is the minimum volume?

    1. A. 15.00 cubic inches
    2. B. 21.75 cubic inchesKeyed answer
    3. C. 18.00 cubic inches
    4. D. 20.25 cubic inches

    Small conductors are 2 × 3 = 6.00. Large conductors are 4 × 2.25 = 9.00. Device and grounds add 3 × 2.25 = 6.75. Total 21.75 cubic inches. Article 314 uses the larger conductor for the device and grounding allowances. The volumes are printed in the stem.

    Open NEC 2026 Article 314

19. 19 · Boxes and wiring methods · Calculations

    This drill allows 360 degrees of bend between pull points. A crowded mechanical room already has bends of 90, 90, 90, and 165 degrees. How many degrees over 360 is that total?

    1. A. 435 degrees over
    2. B. 180 degrees over
    3. C. 75 degrees overKeyed answer
    4. D. 0 degrees over

    90 + 90 + 90 + 165 = 435 degrees. 435 − 360 = 75. The run is 75 degrees over the drill, so you need another pull point. Confirm the bend total for the raceway in NEC 2026. The 360 degree limit is printed in the stem.

    Open NEC 2026 Article 358

20. 20 · Boxes and wiring methods · Calculations

    This drill allows 0.75 square inches of conductor area. Each conductor takes 0.05 square inches, and the crew is pulling 18 of them. How many square inches over the allowance is that pull?

    1. A. 0.90 square inches
    2. B. 0.75 square inches
    3. C. 0.85 square inches
    4. D. 0.15 square inchesKeyed answer

    18 × 0.05 = 0.90 square inches used. 0.90 − 0.75 = 0.15 square inches over the allowance. The allowance itself is not the area you used. Confirm raceway fill in NEC 2026. Both figures are printed in the stem.

    Open NEC 2026 Article 358