Wiring Methods and Materials practice questions (Articles 358–371)

Correct: C — Extending the fastening distance to 5 ft (1.5 m)

358.30(A) allows the near-termination fastening distance to be increased from 3 ft to 5 ft on unbroken lengths when structural members don't readily permit fastening within 3 ft. It doesn't allow skipping the fastener, jumping straight to the 10 ft general interval near a termination, or fishing outside of concealed, impracticable-to-secure work.

Correct: D — Approved supplementary corrosion protection

358.10(B)(2) requires aluminum EMT to have approved supplementary corrosion protection when encased in concrete or in direct contact with earth. The noncinder concrete cover and 18 in. burial depth are the cinder-fill protection options under 358.10(C), not the aluminum rule, and aluminum is explicitly called out separately from galvanized/stainless steel.

Correct: C — Yes, because the total is 315 degrees, which is under the 360-degree limit

Two 90s, one 45, and another 90 total 315 degrees, which stays under the 360-degree cap set by 358.24(B). There's no separate rule limiting the number of bends by count rather than degrees, and the 360-degree limit applies to EMT runs directly under this section, not just other raceway types.

Correct: D — When the location is not subject to severe corrosive influences

358.14 permits steel (galvanized, painted, powder or PVC coated) boxes and enclosures with stainless steel EMT specifically when not subject to severe corrosive influences. There's no blanket ban requiring stainless boxes everywhere, no outdoor-specific carve-out, and separate grounding isn't the qualifying condition.

Correct: A — The percentage fill specified in Table 1, Chapter 9

358.22 explicitly ties the conductor count to the percentage fill specified in Table 1, Chapter 9 — not a flat conductor count, trade size alone, or an ampacity table (ampacity tables address current-carrying capacity, not fill).

Correct: B — Stainless steel

Section 358.100 permits EMT to be made of steel with a protective coating, aluminum, or stainless steel. Rigid PVC, cast iron, and brass are not listed materials for EMT construction.

Correct: A — 358.42

358.42 covers the make-up-tight requirement for EMT couplings and connectors, including the wet-location tightness reference to 314.15; 358.10(D) only addresses where EMT itself is permitted in wet locations, not fitting tightness.

Correct: D — No, FMT is limited to 1.8 m (6 ft)

360.12(6) prohibits FMT in lengths over 1.8 m (6 ft), so an 8 ft run is not permitted regardless of support spacing. FMT has no blanket ban on motor connections — the issue here is purely the length.

Correct: C — 250.118(A)(7)

360.60 permits FMT to serve as an equipment grounding conductor only when the installation meets 250.118(A)(7). 300.15 governs splices and taps (that's 360.56's cross-reference, not grounding), 250.122 is the EGC sizing table for a separate conductor, and 300.11 covers securing and supporting raceways.

Correct: D — Table 360.24(A), for infrequent flexing use

Per 360.24(A), FMT that is infrequently flexed in service after installation must use the radii in Table 360.24(A). The fixed-bend table, 360.24(B), only applies to bends formed during installation that are not flexed afterward — not to bends at moving equipment. There's no rule allowing the installer to pick whichever table is smaller, and bend radius requirements apply regardless of termination.

Correct: D — Table 348.22

Per 360.22(B), 3/8 trade size (metric designator 12) FMT uses the fixed conductor counts in Table 348.22, not the Chapter 9 percentage-fill method. Table 1, Chapter 9 applies only to 1/2 and 3/4 trade size FMT under 360.22(A). Table 310.16 covers ampacity, not fill, and Table 300.5 covers burial depths — neither applies here.

Correct: B — 900 mm (3 ft)

Per 362.30(A), ENT shall be securely fastened at intervals not exceeding 900 mm (3 ft). The 1.8 m (6 ft) figure is a distractor pulled from the luminaire-tap and ceiling-connection exceptions, not the general fastening interval.

Correct: A — Only if the walls provide a thermal barrier with at least a 15-minute finish rating

Per 362.10(2), in buildings exceeding three floors above grade, ENT must be concealed within walls, floors, and ceilings that provide a thermal barrier with at least a 15-minute finish rating. Without that rating (or building-wide sprinklers, per 362.10), it isn't permitted — but a rated barrier does allow it, so 'never permitted' is wrong, and the 3-floor exposed-work allowance and conductor temperature rating (which is a separate rule under 362.10(10)) don't apply here.

Correct: B — The tubing must not be damaged and its internal diameter must not be effectively reduced

362.24(A) allows manual bending with no auxiliary equipment, but the tubing can't be damaged or have its internal diameter effectively reduced. There's no rule requiring a listed bending tool, heat-forming, or a minimum inspected bend count.

Correct: D — At least every 3 m (10 ft)

362.120 requires marking at least every 3 m (10 ft), referencing the first sentence of 110.21(A). The 5 ft, 20 ft, and ends-only options are all more or less frequent than the actual code-required interval.

Correct: D — 362.12

362.12(7) is the uses-not-permitted rule that bars ENT exposed to direct sunlight unless it is listed as sunlight resistant. 362.10 lists where ENT IS permitted (a different question), and 362.6/362.120 cover listing and marking generally, not the sunlight restriction itself.

Correct: D — 362.46

362.46 is the section titled Bushings, requiring a bushing or adapter at box/enclosure entries unless the enclosure itself provides equivalent protection. 362.30(A) covers securing the tubing itself (support), and 362.48/362.24(A) cover joints and bend-making, not entry protection.

Correct: C — The gutter must be listed and marked as suitable for outdoor use

Per 366.10(B)(1), nonmetallic auxiliary gutters are permitted outdoors only where listed and marked as suitable for that purpose. This is stricter than the sheet metal rule in 366.10(A)(1), which permits outdoor use without a special listing.

Correct: B — No adjustment factors apply, since the count does not exceed 30

Under 366.23(A), the 310.15(C)(1) adjustment factors apply only when current-carrying conductors exceed 30 at a cross section. With 28 conductors, the threshold isn't met, so no adjustment factor is required. Sheet metal gutters are not always subject to adjustment factors, and the rule isn't limited to neutrals only.

Correct: D — Where the splices are accessible by removable covers or doors

366.56(A) permits splices or taps within gutters where they're accessible by removable covers or doors, with the added condition that conductors, splices, and taps together not exceed 75% fill. The 12-inch-from-end idea and the 40%-fill-before-splicing option aren't rules in this section, and gutters don't have to be splice-dedicated.

Correct: A — 50 mm (2 in.)

Per 366.100(E), bare current-carrying parts of different voltages mounted on the same surface need at least 50 mm (2 in.) between them. 25 mm (1 in.) is the smaller clearance that applies only to parts held free in the air, not surface-mounted ones.

Correct: A — 300 mm (12 in.)

366.100(B) caps fastener spacing at 300 mm (12 in.) for rivets, bolts, or screws holding the gutter assembly together. The larger spacings would leave corner joints and seams insufficiently secured, and 150 mm (6 in.) is tighter than the code requires.

Correct: D — 20 percent

Per 366.22(A), the sum of cross-sectional areas of all conductors and cables at any cross section shall not exceed 20 percent of the sheet metal auxiliary gutter's interior cross-sectional area. The other percentages are fill limits from other raceway contexts (like conduit fill tables) and don't apply here.

Correct: D — 366.58(B)

366.58(B) governs auxiliary gutters used as pull boxes, requiring the spacing between entries enclosing the same conductor to meet the straight- and angle-pull distances of 314.28(A)(1) and (A)(2). 366.58(A) instead addresses conductors deflected at gutter ends or bends, and 366.30(A)/366.22(A) cover supporting and conductor fill, not pull spacing.

Correct: A — 1.8 m (6 ft)

Per 368.56(B)(2), the length from a busway plug-in device to the tension take-up support device is capped at 1.8 m (6 ft). The extended-length allowance with 2.5 m (8 ft) support intervals only applies in industrial establishments with qualified-persons maintenance, not commercial buildings.

Correct: C — 368.17(D)

368.17(D) governs overcurrent protection ratings for busway used as a branch circuit, referring to 210.20. 368.17(A) instead covers feeder ratings, and 368.17(C) covers tap devices for feeder or branch circuits rather than the branch circuit's own OCPD rating.

Correct: D — Overcurrent protection at the point of ampacity reduction

368.17(B) requires overcurrent protection at ampacity reduction points as the general rule. The 50-ft-and-one-third exception only applies to industrial establishments, not commercial buildings, so none of the exception conditions excuse this installation.

Correct: A — It must be interlocked to prevent operation under load

368.239 requires that switching devices which are not load-break be interlocked so they cannot be operated while carrying load. There's no derating requirement, no relabeling as a disconnecting link, and no 6-foot load-break substitution rule in this section — those are distractors, not code text.

Correct: B — Only if specifically approved for that use

368.12(C) prohibits busway in hazardous (classified) locations unless it is specifically approved for such use. The 8 ft clearance rule in 368.12(E) applies to lighting and trolley busway height, not to hazardous location approval, and conductor material has no bearing on this permission.

Correct: D — Electrical nonmetallic tubing (ENT)

368.56(A) lists ENT among the 16 permitted wiring methods for busway branches. Type NM, SE, and UF cable are not on that list, even though they are common wiring methods elsewhere in the Code.

Correct: A — A drain plug, filter drain, or similar method to remove condensed moisture

368.236 requires drain plugs, filter drains, or similar methods at low points in a busway run to remove condensed moisture. Ventilation requirements under 368.237 apply to ventilated bus enclosures generally, not specifically to low points, and expansion fittings and inspection junction boxes address different concerns entirely.

Correct: B — Ambient temperature at the installation site

368.320 requires rated voltage, rated continuous current, rated frequency, rated impulse withstand voltage, rated 60-Hz withstand voltage (dry), rated momentary current, and the manufacturer's name or trademark. Installation-site ambient temperature is not one of the listed nameplate items.

Correct: B — 368.258

368.258 specifically requires the neutral bus to be sized for all neutral load current, including harmonics, with adequate momentary and short-circuit rating. 368.260 covers grounding of the busway enclosure (not neutral sizing), and 368.17(A) addresses overcurrent protection ratings for feeders, not neutral conductor sizing.

Correct: C — Only when the enclosure is other than Type 1

369.120(7) requires the enclosure type designation only if it is other than Type 1 — Type 1 enclosures need no separate marking. The other options describe conditions not tied to this marking requirement.

Correct: D — Extended vertically through a dry floor, totally enclosed in metal at the floor and for 6 ft above it

369.10(4) permits IBP extended vertically through dry floors when totally enclosed in metal at the floor penetration and for a minimum of 6 ft above it. Using IBP to support luminaires, concealing it in the building structure, and installing it in hazardous locations outside other applicable articles are all barred by 369.12.

Correct: B — 369.110

369.110 is the specific rule requiring fire barriers wherever fire walls, floors, or ceilings are penetrated. 369.100 (Construction) covers physical build requirements for the wireway itself, not fire-stopping at penetrations, so it doesn't answer this scenario.

Correct: A — That it be listed

369.6 requires that IBP and IBP systems be listed. Field testing by an engineer and manufacturer reconditioning aren't recognized substitutes, and there's no outdoor-only restriction in this section.

Correct: B — The structure must be specifically designed for the required span length

370.30(A) sets the default maximum at 3.7 m (12 ft) but allows longer spans if the structure is specifically designed for that span length — it isn't an automatic extension or a rule tied to a stamp threshold.

Correct: B — The cablebus's engineered design

370.22 states the number of conductors shall be that for which the cablebus is designed — there's no separate percent-fill calculation like the raceway fill values in Chapter 9, Table 1, or the 40% conduit-fill limit, because cablebus is an engineered support assembly, not an enclosed raceway.

Correct: B — No, because 1/0 is the smallest conductor size permitted in cablebus regardless of design

370.20(A)(2) lets cablebus conductor size follow the engineered design, but sets an absolute floor: never smaller than 1/0. A No. 2 AWG conductor is smaller than 1/0 and is not allowed no matter what the ampacity math shows. There's no requirement to match a Table 310.16 maximum.

Correct: C — A straight horizontal run with no direction change, termination, or damage exposure

370.42 requires fittings for direction changes, terminations at equipment or enclosures, and added protection where exposed to severe physical damage. A plain straight run with none of those conditions has no fitting requirement under this section.

Correct: A — 370.60

370.60 is the grounding section, covering use of a bonded cablebus framework as the equipment grounding conductor and requiring compliance with Article 250, Parts V and VI. 370.30 addresses securing and supporting the cablebus, not grounding.

Correct: C — 371.17(B)

371.17(B) sets the overcurrent protection rule for flexible bus systems installed as feeders, referencing 215.3, while 371.17(A) governs services and 371.17(C) governs branch circuits — different applications of the same flexible bus product.

Correct: C — 240.21(C), the secondary conductor protection rules

Per 371.17(D), flexible bus on a transformer secondary ahead of the disconnect and OCPD is protected in accordance with 240.21(C), the transformer secondary conductor rules. The 240.21(H) battery rule and the 445.12 generator rule apply to different source types under 371.17(F) and 371.17(E), and unprotected runs aren't permitted.

Correct: D — 450 mm (1 1/2 ft)

371.30 sets vertical support spacing at 450 mm (1 1/2 ft), tighter than the 900 mm (3 ft) horizontal spacing, unless the product listing permits otherwise. 900 mm is the horizontal figure, not vertical, and the other distances aren't code values from this section.

Correct: C — The bus system must be identified for outdoor use

371.10(3) permits outdoor use only where the flexible bus system is identified for outdoor use. It's not a blanket prohibition, a wet-location rating alone doesn't satisfy the outdoor requirement, and the permitted-use list in 371.10(1) applies equally to services, feeders, and branch circuits without restricting outdoor use to services only.

Correct: B — A qualified engineer

371.14 requires flexible bus systems to be designed and specified for the specific installation site by a qualified engineer. The contractor performs the installation, the manufacturer's rep isn't the designer of record, and the AHJ reviews documentation rather than creating the design.

Correct: A — Design engineering supervision and the manufacturer's instructions

371.18(A) requires flexible bus systems to be installed under design engineering supervision and in accordance with the manufacturer's instructions, including supporting and securing. There's no separate requirement for pre-purchase inspector approval, for a master electrician to personally make every connection, or for field modifications keyed only to ampacity — those aren't what this section conditions the install on.

Correct: B — Curbs to prevent waterflow through the opening, plus a means to seal the floor penetration

371.18(E) requires both curbs (or another means to stop waterflow through the opening) and a means to seal the penetration itself. The 'continuous and protected' standard is the requirement for transverse wall penetrations under 371.18(C), not wet-location floor penetrations — it doesn't satisfy the wet-location rule on its own.

Correct: D — The reduced-size portion is 15 m (50 ft) or less, rated at least one-third of the upstream device, and free from contact with combustible material

371.17(G) permits omitting overcurrent protection at a size reduction only in industrial establishments, and only when the reduced-size flexible bus run does not exceed 15 m (50 ft), carries a rating of at least one-third the upstream overcurrent device, and stays clear of combustible material. The one-half rating figure and the raceway-enclosure condition are not part of this exception; they're confusions with other tap-style rules.