Wiring Methods and Materials practice questions (Articles 305–330)

Correct: C — A stress reduction means

305.10 requires stress reduction means (such as a stress cone) at all terminations of factory-applied shielding to control the electrical stress created where the shield ends. Re-wrapping the cut end in tape or leaving an air gap doesn't address that stress concentration and isn't the code's requirement.

Correct: D — 305.15(A)

Table 305.15(A), Minimum Cover Requirements, is located at 305.15(A) and governs burial depth. 305.15(B) covers wet-location conductor use, not cover depth, and 305.15(C) addresses physical damage protection rather than burial depth.

Correct: B — 2.5 m (8 ft) above finished grade

305.15(C) requires pole-mounted raceway to extend from the minimum cover depth in Table 305.15(A) up to 2.5 m (8 ft) above finished grade. The shorter heights are common confusions with other clearance rules but don't match this section's stated distance.

Correct: A — 305.4

305.4 lists the specific exceptions permitting different voltage systems to share an enclosure, including item (4) covering manholes where conductors are permanently separated and secured to supports. 305.15(A)(2) instead addresses industrial establishment cable assembly requirements for underground installations, not enclosure-sharing rules.

Correct: A — Suitable materials with a watertight, mechanically protected splice

305.15(D) permits direct-buried cables to be spliced or tapped without a splice box, provided suitable materials are used and the splice is watertight and protected from mechanical damage. A splice box, above-grade location, or duct encasement is not the code requirement here.

Correct: B — 305.15(B)

305.15(B) is the rule that classifies the interior of underground enclosures and raceways as a wet location and sets the wet-location listing requirement for conductors, cables, and splices. 305.15(D) only covers splice methods/materials, not the wet-location classification itself, and 305.8 addresses raceways in wet locations above grade, not underground.

Correct: C — 305.8

305.8 states that raceways installed in wet locations above grade have interiors considered wet locations, requiring moisture-impervious metal-sheathed conductors or conductors listed for wet locations. 305.11 addresses moisture/mechanical protection specifically for metal-sheathed cables, not general raceway wiring, and 305.15(B) covers wet locations for underground installations, not above grade.

Correct: C — 312.6(B)(2)

312.6(B)(2) governs wire-bending space when a conductor enters or leaves the enclosure through the wall opposite its terminal, directing the installer to Table 312.6(B)(2). 312.6(B)(1) instead applies Table 312.6(A) only when the conductor does NOT enter/leave opposite its terminal, so it doesn't fit this scenario.

Correct: B — 40 percent of the cross-sectional area

Per 312.8(A)(1), conductors alone at any cross section of the wiring space are limited to 40 percent fill. The 75 percent figure applies only when splices and taps are included with the conductors under 312.8(A)(2); a label alone does not remove the fill limit.

Correct: C — 1.00 in.

312.101(A)(3) increases the live-part airspace to at least 1.00 in. for nominal voltages of 251 to 1000, compared to 0.500 in. at 250V or below. The 0.500 in. spacing only carries over to higher voltage (up to 600V) if the 312.101(A)(2) exception conditions are met, which this scenario rules out.

Correct: B — 1.35 mm (0.053 in.)

312.100(B) sets the minimum uncoated sheet steel thickness at 1.35 mm (0.053 in.) to ensure ample strength and rigidity. The other values are not the code-specified threshold.

Correct: A — 312.5(C)

312.5(C) is the cable section that spells out the seven conditions permitting nonmetallic-sheathed cable to enter a surface-mounted enclosure through a short nonflexible raceway nipple. 312.5(A) covers closing unused openings and 312.5(B) covers metal cabinet installation generally — neither addresses the raceway-nipple exception, and 312.6(C) deals with bending space for 4 AWG and larger conductors, not cable entry method.

Correct: A — Provide at least 6 mm (1/4 in.) of airspace between the box and the wall

Per 312.2, surface enclosures in damp or wet locations need at least a 6-mm (1/4-in.) airspace off the mounting surface. The airspace exception for mounting directly on masonry, concrete, or tile applies only to nonmetallic enclosures, not metallic ones, so this metallic box still needs the airspace. There's no 25-mm threshold in this section.

Correct: B — 312.5(A)

312.5(A) requires all openings through which conductors enter to be closed in an approved manner. 312.5(B) only addresses bushing requirements for messenger-supported, open, or knob-and-tube wiring entering metal enclosures, not general unused openings, and 312.4 covers repairing noncombustible surfaces after cabinet removal, not closing knockouts.

Correct: A — 312.10

312.10 governs field-installed screws or other fasteners entering wiring spaces, requiring blunt ends and limiting penetration depth. 312.5(A) covers closing unused openings in cabinets, not fastener protrusion into wiring space, and 312.8 addresses usable space in switch and overcurrent device enclosures, not fastener design.

Correct: C — It must be identified as a field-installable accessory or a listed kit evaluated for that installation

312.8(B)(1) requires the power monitoring or energy management equipment to be identified as a field-installable accessory of the listed equipment, or be a listed kit evaluated for field installation in that enclosure. General UL listing without enclosure-specific evaluation, factory-only installation, and AHJ discretion without a listing requirement are not what the rule specifies.

Correct: B — The 60°C rated ampacity, even though the conductors are 90°C rated

Per 320.80(A), conductors in thermal insulation must be rated 90°C, but the ampacity used still cannot exceed that of a 60°C rated conductor. The 90°C rating is only usable for adjustment and correction calculations, not for picking a higher final ampacity — ruling out the 90°C option. There is no 75°C compromise or installer's choice under this section.

Correct: D — 1.4 m (4½ ft)

320.30(C) requires Type AC cable to be supported at intervals not exceeding 1.4 m (4½ ft). The 300 mm figure is the securing distance from boxes under 320.30(B), not the general support interval, and the 1.8 m and 600 mm figures are the unsupported-length allowances under 320.30(D) for ceiling drops and flexible terminals, not general support spacing.

Correct: C — 320.23(A)

320.23(A) governs cable run across the top of framing members and limits the guard-strip requirement to within 6 ft of the scuttle hole when the attic is not accessible by permanent stairs or ladder — beyond that distance no guard strips are required. 320.23(B) instead covers cable run parallel to framing members, a different installation method with no guard-strip requirement.

Correct: D — The insulating bushing between conductors and armor

320.40 requires the connector or clamp to be designed so the insulating bushing (anti-short bushing) is visible for inspection. Manufacturer markings, conductor counts, and box fill labels aren't inspection points under this section.

Correct: B — A damp or wet location

320.12(2) prohibits Type AC cable in damp or wet locations because its armor and internal paper wrap don't protect against moisture intrusion. Dry basements, dry framed walls, and accessible attics aren't damp or wet locations, so none of them trigger this prohibition.

Correct: B — Embedded in plaster finish on brick in a wet location

320.10(4) permits AC cable embedded in plaster finish on brick or masonry, but specifically excepts damp or wet locations. Feeders and branch circuits (exposed or concealed) and cable tray installations are all listed as permitted uses under 320.10.

Correct: D — Black

Per 322.120(C), the terminal block sequence runs white (grounded conductor), then black for the next adjacent section, then red, then blue for the final outer section. Red and blue belong to later sections, and gray is not part of the terminal block sequence at all — it relates to conductor marking under 322.120(B), not terminal blocks.

Correct: C — In a junction box installed at either end of the flat cable assembly run

322.40(D) requires all extensions from flat cable assemblies to be made by approved wiring methods within junction boxes installed at either end of the FCA run — not mid-run splices, not at the panelboard, and not inside the raceway without a box.

Correct: B — Five

322.100 limits Type FC flat cable assemblies to two, three, four, or five conductors — five is the maximum. Three and four are within the permitted range but not the maximum, and six exceeds it.

Correct: D — Inside a listed junction box

322.56(A) requires that splices be made in listed junction boxes. Tap devices identified for the use are for taps, not splices (322.56(B)), and open-air taping or terminal-bar splicing isn't a listed junction box.

Correct: C — 324.10(A)

324.10(A) is the specific provision stating FCC systems are permitted for general-purpose, appliance, and individual branch circuits; 324.10(B)(2) instead sets the ampere ratings for those circuits, and 324.12 covers uses NOT permitted.

Correct: A — Only when the FCC is enclosed in a surface metal raceway

Per 324.10(D), FCC on wall surfaces is permitted only inside surface metal raceways. The damp-location allowance in 324.10(E) is a separate permission that doesn't apply to wall mounting, and the hard/smooth/sound floor requirement in 324.10(C) applies to floors, not walls.

Correct: A — Completely cover all cable runs, corners, connectors, and ends

324.40(C)(1) requires the top shield to completely cover all cable runs, corners, connectors, and insulating ends, not just splices or transition points. Partial coverage options like splice-only or threshold-only protection don't meet this requirement.

Correct: D — 324.12

324.12 lists the locations where FCC systems are prohibited, including school and hospital buildings other than administrative office areas. 324.10(E) only addresses damp locations for permitted installations, and 324.1 is just the article's scope statement, neither of which lists the prohibited-use categories.

Correct: A — A new cable connector

324.56(A) requires new cable connectors at new connection points when altering FCC systems. Reusing an old connector, taping a field splice, or skipping a connector entirely are not what the section permits.

Correct: A — At least one of the four conductors must be an equipment grounding conductor

324.100(A) requires Type FCC cable to consist of three, four, or five flat copper conductors, one of which is an equipment grounding conductor — not two, and not zero.

Correct: B — Sealing it with a listed insulating end

324.40(A) specifically requires bare cable ends to be insulated and sealed against dampness and liquid spillage using listed insulating ends. Tape or floor covering alone doesn't meet this identified-product requirement, and being under carpet squares doesn't exempt the end from needing a listed insulating end.

Correct: C — 1.0 m (39.37 in.) square

324.41 caps carpet squares over Type FCC cable at 1.0 m (39.37 in.) square. The smaller 0.5 m and larger 1.2 m options are plausible but don't match the code text, and unlimited size is not permitted since oversized squares are excluded by the rule.

Correct: B — Table 1, Chapter 9

326.116 splits the job into two tables: Table 326.116 gives the conduit's own fill dimensions, while the percent-fill cap the conductors can't exceed comes from Table 1, Chapter 9 — the same fill limits used across other raceway types. Table 310.16 covers ampacity, not fill, and Table 300.5 covers underground burial depths.

Correct: B — No more than the equivalent of four quarter bends (360 degrees total), including bends at the pull boxes

326.26 caps a run between pull boxes or terminations at the equivalent of four quarter bends (360 degrees total), and explicitly includes bends located immediately at the pull box or terminations. Excluding those bends, applying a per-100-foot allowance, or assuming radius compliance alone is sufficient are all misreadings of 326.26.

Correct: C — 326.10

326.10 (Uses Permitted) lists underground service-entrance, feeder/branch-circuit, and underground service conductors as permitted applications for Type IGS cable. 326.1 is only the scope statement, not the list of permitted uses.

Correct: C — Within 300 mm (12 in.) of the box

Under 330.30(B), cable with four or fewer conductors sized no larger than 10 AWG must be secured within 300 mm (12 in.) of every box, cabinet, fitting, or termination — not just the general 6-ft interval. The 10-ft spacing only applies to listed vertical runs with 250 kcmil+ ungrounded conductors, which doesn't fit this smaller cable.

Correct: B — The installation must not exceed the equipment's temperature rating, regardless of the conductor's calculated ampacity

330.80 is explicit: the installation shall not exceed the temperature ratings of terminations and equipment, even if 310.14 or 315.60 would otherwise permit a higher ampacity. Switching tables or routing methods doesn't override this termination limit.

Correct: B — 12 times

Per 330.24(A)(2), smooth-sheath cable more than 19 mm (3/4 in.) but not more than 38 mm (1-1/2 in.) in external diameter uses 12 times the diameter. The 10 times multiplier applies only to cable at or under 19 mm, 15 times applies only above 38 mm, and 7 times is the interlocked/corrugated rule, not smooth sheath.

Correct: C — The metallic covering is impervious to moisture

Per 330.10(A)(11), a corrosion-resistant jacket alone isn't enough in a damp or wet location — one of three extra conditions must also be met, including a moisture-impervious metallic covering. Messenger support and cable tray relate to other permitted uses in 330.10(A)(6) and (8), and embedding in plaster applies to dry locations only under 330.10(A)(10).

Correct: A — Perforated metallic sheath

330.116 lists only three permitted metallic covering types: smooth metallic sheath, corrugated metallic sheath, and interlocking metal tape armor. A perforated sheath is not one of the recognized types.

Correct: A — Article 392, Cable Trays

Per 330.10(B)(1), MC cable installed in cable tray must comply with specific subsections of Article 392 (392.10, 392.12, 392.18, 392.20, 392.22, 392.30, 392.46, 392.56, 392.60(C), and 392.80). Relying on Article 330 alone misses the tray-specific fill and support rules, and Article 300 and Article 725 don't govern cable tray installations.

Correct: B — The unsupported length does not exceed 1.8 m (6 ft) from the last point of support

330.30(D)(2) permits up to 1.8 m (6 ft) of unsupported MC cable from the last support point to the luminaire connection, provided both are within an accessible ceiling. The 900 mm (3 ft) limit applies instead to the interlocked-armor flexibility exception in 330.30(D)(3), and a concealed, unreachable space is the basis for the fished-cable exception in 330.30(D)(1), not this one.

Correct: B — Free airspace of not less than 2.15 times the diameter of the largest conductor in the configuration

330.80(B) requires maintained free airspace of not less than 2.15 times the diameter (2.15 × O.D.) of the largest conductor in the configuration, not the smallest, and not a flat 1-inch or single-diameter spacing rule.

Correct: D — 330.104

330.104 sets the minimum conductor sizes for MC cable (14 AWG copper, 12 AWG aluminum/copper-clad aluminum). 330.108 only addresses what qualifies as the equipment grounding conductor, not minimum sizing, and 330.112 covers insulation types rather than conductor size.