Wiring Methods and Materials practice questions (Articles 372–393)

Correct: B — In a straight line at right angles to the cells

372.18(A) requires the header to be installed in a straight line at right angles to the cells. Running it parallel, diagonal, or in an arbitrary direction does not meet this installation requirement.

Correct: A — By an equipment grounding conductor or bonding jumper to a positive ground connection on the header

372.18(D) requires an equipment grounding conductor or bonding jumper connecting insert receptacles to a positive ground connection on the header. Concrete contact, a separate ground rod, and relying on the insert body alone are not recognized grounding paths under this section.

Correct: A — By the combined cross-sectional area of all conductors and cables not exceeding 40 percent of the cell or header area

372.22 measures fill as the combined cross-sectional area of all conductors or cables against the cell or header's own cross-sectional area, capped at 40 percent. This is not a conduit-fill-table calculation, a conductor-count rule, or based on a single conductor's area.

Correct: C — 372.58

372.58 specifically requires that conductors supplying a discontinued outlet be removed from the raceway, with no splices or reinsulated conductors left in place. 372.56 covers splices and taps for conductors still in service, and 372.18(D) addresses inserts for cellular concrete floor raceway installation, not abandoned-outlet conductor removal.

Correct: C — Water or concrete

372.18(C) specifically requires junction boxes to be sealed against the free entrance of water or concrete, since these boxes sit at floor level during pours. Dust, insulation, and conduit fill are not the hazards this rule addresses.

Correct: B — 374.18(A)

374.18(A) specifically lists the permitted wiring methods — including liquidtight flexible nonmetallic conduit listed and marked for direct burial when installed in concrete — for connecting cellular metal floor raceways to cabinets and wall outlets. 374.18(B) covers junction boxes and 374.18(C) covers inserts, not the connection wiring method; 374.56 governs splices and taps within the raceway itself, not the riser connection to a cabinet.

Correct: A — It must be leveled to floor grade and sealed against the free entrance of water or concrete

374.18(B) requires junction boxes to be leveled to floor grade and sealed against the free entrance of water or concrete, and to be metal and electrically continuous with the raceway. Leaving sealing to others, allowing a nonmetallic box, or sealing against concrete alone all omit part of the actual requirement.

Correct: C — Only in header access units or junction boxes

374.56 restricts splices and taps to header access units or junction boxes. There's no general allowance for splicing anywhere accessible, no special loop-wiring-entry exception, and no 300 mm distance rule in this section.

Correct: A — An area subject to corrosive vapor

374.12(1) prohibits conductors in cellular metal floor raceways where subject to corrosive vapor. The other listed areas aren't among the prohibited-use conditions in this section.

Correct: C — The sum of cross-sectional areas of all conductors and cables cannot exceed 20% of the wireway's interior cross-sectional area at any cross section

376.22(A) caps wireway fill at 20% of interior cross-sectional area at any cross section — not 40% (a conduit-fill-style figure that doesn't apply here), not a conductor count, and not an average over the run since the rule applies at any cross section.

Correct: B — 376.56(B)(1)

376.56(B)(1) requires power distribution blocks in metal wireways to be listed, and marked for line-side service use when installed ahead of the service equipment. 376.56(A) instead governs splices and taps (not distribution blocks), and 376.56(B)(4) addresses exposed live parts rather than listing/marking.

Correct: B — 300 mm (12 in.)

376.100(B) requires corner joint fasteners (rivets, bolts, or screws) to be spaced not more than 300 mm (12 in.) apart. The 150 mm option is too tight and not a code figure here, while 450 mm and 600 mm exceed the maximum allowed spacing and would risk gaps in the enclosure.

Correct: A — Dimensions corresponding to one wire per terminal in Table 312.6(A)

Per 376.23(A), a deflection greater than 30 degrees at a raceway entry requires dimensions corresponding to one wire per terminal in Table 312.6(A). The 314.28(A) distance formulas apply instead to wireways used as pull boxes for 4 AWG and larger conductors under 376.23(B), not to deflection at entries.

Correct: B — 3 m (10 ft)

Per 376.30(A), even when individual lengths longer than 5 ft are supported at each end or joint instead of at 5 ft intervals, the distance between supports still cannot exceed 3 m (10 ft). The 5 ft figure is the standard interval, not the max gap for this case, and 15 ft and 20 ft are well beyond the horizontal limit.

Correct: A — When the wireway is listed for that purpose, per 250.118(A)(13)

376.60 permits listed metal wireway to serve as an equipment grounding conductor in accordance with 250.118(A)(13) — the listing is the key qualifier, not simply being metal. A separate bonding jumper or an industrial-only condition is not part of this permission as stated in these sections.

Correct: D — 20 percent of the interior cross-sectional area

378.22 sets the nonmetallic wireway fill cap at 20 percent of the interior cross-sectional area. The 40 percent figure is a conduit-fill number from a different chapter, not wireway, and the exterior-area option misstates that the rule is based on interior area.

Correct: C — 6 mm (0.25 in.) or greater

378.44 sets the threshold at 6 mm (0.25 in.) or greater expected length change in a straight run. The 3 mm and 13 mm figures are both plausible-sounding but wrong thresholds, and 'any measurable amount' overstates the rule — small movements below 1/4 in. don't trigger the requirement.

Correct: D — 378.60

378.60 (Grounding) requires a separate equipment grounding conductor in the nonmetallic wireway unless the grounded conductor is permitted to ground equipment under 250.142. 378.70 covers grounding only for extensions leaving the wireway via cord pendants or Chapter 3 wiring methods, not conductors run within the wireway itself.

Correct: D — No, because 378.23(B) only applies to conductors 4 AWG or larger

378.23(B) sets its pull-box distance requirement specifically for insulated conductors 4 AWG or larger; 6 AWG falls below that threshold, so the rule doesn't trigger. The wireway's material isn't the deciding factor, and wireways are explicitly addressed by this section as functioning like pull boxes when the size threshold is met.

Correct: D — 378.20

378.20 directly addresses parallel single-conductor cables in nonmetallic wireway, requiring each group to contain no more than one conductor per phase, neutral, or grounded conductor to avoid inductive imbalance. 378.22 (Number of Conductors) governs fill/derating, not paralleling groups, and 378.21 covers conductor sizing, not arrangement.

Correct: B — When it is metal and the building finish surrounds the back and sides

Per 380.12(1), a metal multioutlet assembly may have its back and sides surrounded by building finish; the exception for a nonmetallic assembly is recessing into a baseboard, not general wall concealment. Hoistways are separately prohibited, and voltage under 50 volts has no bearing on this exception.

Correct: A — Dimensions corresponding to one wire per terminal in Table 312.6(A) apply

Per 380.23(A), any deflection greater than 30 degrees in a multioutlet assembly's direction requires dimensions for one wire per terminal from Table 312.6(A) — this applies regardless of conductor size, unlike the pull-box rule in 380.23(B) which is specific to 4 AWG and larger.

Correct: D — Ungrounded conductor at center, sectioned grounded conductor around it, sectioned equipment grounding conductor outermost

382.100 defines the multilayer flat conductor design as a center ungrounded conductor enclosed by a sectioned grounded conductor, with an overall sectioned equipment grounding conductor as the outermost layer. Swapping the grounded and EGC layer order, or centering the grounded conductor, misstates the required layer sequence.

Correct: B — They must be identified for use with concealable nonmetallic extensions

382.42(A) specifically requires that all receptacles, receptacle housings, and self-contained devices used with concealable nonmetallic extensions be identified for this use. Wet-location listing, a minimum 20 A rating, and metal-clad construction are not requirements found in this section.

Correct: C — 200 mm (8 in.)

382.30(A) sets the maximum fastening interval at 200 mm (8 in.). The 300 mm (12 in.) figure is a distractor — it's only the allowed distance to the first fastener where the extension connects to its supplying outlet via an attachment plug, not the general spacing rule.

Correct: C — An unfinished attic

382.12(1) prohibits nonmetallic extensions in unfinished basements, attics, or roof spaces because of exposure to physical damage. Finished spaces like a basement rec room, an office, or a retail floor aren't covered by this prohibition.

Correct: C — The building is occupied for residential or office purposes and does not exceed three floors above grade

382.10(C) permits surface-mounted nonmetallic extensions only in buildings occupied for residential or office purposes, not exceeding three floors above grade. Industrial or warehouse occupancies aren't listed as permitted regardless of floor count, and the 'identified for use above three floors' exception applies only to concealable extensions, not surface-mounted ones.

Correct: A — 382.120(A)

382.120(A) is the specific subsection requiring durable marking on both sides at 610 mm (24 in.) intervals with conductor material, maximum temperature rating, and ampacity. 382.120(B) instead governs individual conductor identification, not the cable's exterior marking, and 382.104/382.112 cover conductor construction and insulation, not marking.

Correct: C — 384.30(A)

384.30(A) sets the 3 m (10 ft) maximum spacing and 900 mm (3 ft) from termination rule specifically for surface-mounted strut-type channel raceway retention straps. 384.30(B) covers suspension mounting instead of surface mounting, and 384.22/384.6 don't address securing intervals.

Correct: C — Rigid PVC

384.100(A) limits strut-type channel raceways and accessories to steel, stainless steel, or aluminum. Rigid PVC is not a listed material for the raceway body itself — PVC is only mentioned in 384.100(B) as an example of an organic coating used to protect steel raceways from corrosion, not as a raceway material.

Correct: C — 384.22

384.22 governs the number of conductors permitted, referencing Table 384.22 for percentage fill and Chapter 9 for conductor area. 384.21 only limits conductor size to what the raceway is listed for, not fill quantity, and 384.6/384.100 deal with listing and construction, not conductor count.

Correct: D — The cover cannot be used as the grounding means for the receptacle mounted in it

384.60 specifically excludes the snap-fit cover from serving as the grounding means for a receptacle mounted in it, even though that same cover can achieve electrical continuity for the raceway system generally. The idea that listed continuity automatically covers the receptacle is the exact confusion this rule addresses.

Correct: A — The length passing through the partition is unbroken and conductors remain accessible on both sides

386.10(4) requires that the length of surface metal raceway passing through a dry wall, partition, or floor be unbroken, and that access to the conductors be maintained on both sides. Fire sealant, independent grounding at each side, and a specific fire-resistance rating are not conditions imposed by this section.

Correct: A — Only if the raceway metal is at least 1.02 mm (0.040 in.) thick

386.12(2) prohibits surface metal raceway at 300 volts or more between conductors unless the metal has a nominal thickness of at least 1.02 mm (0.040 in.). Wet-location listing and added grounding conductors don't address this specific voltage/thickness rule, and the flat 'never' option ignores the thickness exception.

Correct: C — 386.56

386.56 covers splices and taps in surface metal raceway and sets the 75 percent fill limit at the splice point, provided the cover is removable and accessible. 386.22 governs the general number of conductors/cables the raceway can hold (not the splice-specific fill rule), and 386.21 covers conductor sizing, not splice fill.

Correct: D — The sum of conductor cross-sectional areas is 35 percent of the raceway's interior area

Per 386.22, the exception to 310.15(C)(1) adjustment factors requires the sum of conductor cross-sectional areas to be 20 percent or less of the raceway's interior area — 35 percent fails that test. A 3000 mm2 area exceeds the 2500 mm2 minimum (passes), 18 conductors is under the 30-conductor cap (passes), and cable use permitted by its own article is simply allowed under 386.22, not a disqualifier.

Correct: B — 388.12

388.12(1) prohibits surface nonmetallic raceway where concealed, except for the transverse wall/floor extension allowed in 388.10(2). 388.10 covers where it IS permitted (dry locations, transverse extensions), not the concealment prohibition, and 388.6/388.30 cover listing and support, not location restrictions.

Correct: B — 75 percent of the cross-sectional area

388.56 caps conductors, including splices and taps, at 75 percent of the raceway's area at that point. The 40 percent and 53 percent figures are conduit fill percentages used elsewhere in the Code for different conditions, not this section's rule.

Correct: D — Sections must mechanically couple together without subjecting wires to abrasion

388.100 requires that surface nonmetallic raceways, elbows, couplings, and similar fittings be designed so sections mechanically couple together and install without abrading the wires. It does not require solvent welding, metallic fittings, or threaded PVC-style couplings.

Correct: A — The different systems must be run in separate compartments identified by stamping, imprinting, or color coding

388.70 requires that when combination surface nonmetallic raceways carry both signaling and lighting/power circuits, the systems be run in separate compartments identified by stamping, imprinting, or color coding of the interior finish. Insulating signaling conductors for the power voltage, requiring a metallic raceway, or adding a grounded barrier strip are not the rule this section states.

Correct: A — The box must be metal and electrically continuous with the raceway

Per 390.74, junction boxes used with metal raceways must be metal and electrically continuous with the raceway. There's no separate bonding-wire requirement stated, no sealant-fill requirement, and nonmetallic boxes are not the rule for metal raceways.

Correct: C — In a straight line coinciding with the centerline from box center to box center

390.70 requires that a straight line from the center of one junction box to the center of the next coincide with the raceway's centerline. Curves, offsets, or arbitrary shortest paths are not permitted layouts under this section.

Correct: C — 390.10

390.10 is the Uses Permitted section, allowing underfloor raceways in office occupancies when laid flush with the concrete floor and covered with linoleum or equivalent flooring. 390.15(D) instead covers the concrete covering thickness for raceways once installed, not whether the installation itself is permitted.

Correct: D — In junction boxes

390.56 requires splices and taps to be made only in junction boxes, with a narrow exception for trench-type flush raceway with an accessible removable cover. Taping conductors mid-run or landing them at a terminal fitting or outlet body doesn't satisfy this.

Correct: C — Listing as a complete system, or assembling entirely from parts listed for their specific function

393.6 requires the system to be listed either as a complete package under 393.6(A) or built entirely from parts each listed for their appropriate function under 393.6(B). Mixing listed and unlisted components, or assuming low voltage exempts listing, does not satisfy either path.

Correct: C — By straps, staples, hangers, or listed cable ties so it isn't damaged by normal building use

Section 393.14(A) requires cables supported on ceilings and sidewalls to be secured by straps, staples, hangers, cable ties listed and identified for securement and support, or similar fittings that won't damage the cable. Resting cable on grid tees, relying on ceiling suspension wires, or leaving exposed ceiling runs unsupported do not meet this requirement.

Correct: B — No, lighting in general or critical patient care areas is prohibited

393.12(7) prohibits suspended ceiling power distribution systems for lighting in both general and critical patient care areas — there's no GFCI or receptacle-vs-lighting carve-out, and the prohibition covers both area types, not just critical care.

Correct: B — A listed Class 2 lighting fixture rated within the 30-volt ac limit

393.10(1) limits use to listed utilization equipment at 30 volts ac/60 volts dc maximum, within Class 2 power levels, for lighting, control, and signaling circuits only. Standard 120-volt receptacles and Class 1 circuits exceed the Class 2 / low-voltage scope.

Correct: D — Rail-to-rail connector

Per 393.40(A)(4), a rail-to-rail connector interconnects busbars from one ceiling grid rail to another. A load connector feeds utilization equipment, a pendant connector suspends luminaires below the rail, and a power feed connector ties the supply to the distribution cable and busbar — none of those join rail to rail.

Correct: C — Accessible and within sight of the Class 2 power source

393.21(A) requires the disconnecting means to be accessible and within sight of the Class 2 power source, so it's usable for servicing or maintaining the grid system. Placing it elsewhere in the building, at service equipment, or within sight of the load instead of the source does not satisfy this location requirement.