Wiring Methods and Materials practice questions (Articles 394–398)

Correct: C — Substantial running boards extending at least 1 in. on each side

Per 394.23(A), where conductors run through bored holes in joists (and in studs or rafters up to 7 ft above the floor), they must be protected by substantial running boards extending not less than 1 in. on each side. Conduit sleeves aren't the required protection method, and running boards can't be skipped just because the run is through bored holes — that's exactly when they're required. Guard strips alone are not the specified protection; the rule calls for running boards.

Correct: C — If special permission is granted

Per 394.10, concealed knob-and-tube is permitted only for extensions of existing installations or elsewhere by special permission. Since there's no existing K&T to extend, special permission is the only route. Limiting to attic spaces alone doesn't satisfy either permitted condition, and the extension option doesn't apply because no prior K&T installation exists.

Correct: C — 4 1/2 ft

394.30(A)(2) caps support intervals at 1.4 m (4 1/2 ft). The 150 mm (6 in.) figure is a distractor from the separate rule about spacing near taps and splices, not the general interval spacing.

Correct: B — 75 mm (3 in.)

394.19(A) sets the conductor-to-conductor clearance at 75 mm (3 in.). The 25 mm (1 in.) figure is the separate clearance required between a conductor and the surface it passes over, not between conductors.

Correct: A — A licensed professional engineer engaged primarily in the design of such systems

395.30(A) requires the documentation to be by a licensed professional engineer engaged primarily in the design of such systems — a general PE license or the contractor's own sign-off doesn't satisfy this. The AHJ only requests and reviews the documentation; it doesn't produce it.

Correct: C — Applied phase-to-phase voltage, mechanical strength for the installation, and impulse withstand BIL

395.30(C) requires insulators to be rated for applied phase-to-phase voltage, the mechanical strength needed for that specific installation, and impulse withstand BIL per Table 495.24. Phase-to-ground voltage alone, conductor ampacity, and conduit fill are not the criteria this section sets for insulators.

Correct: C — No, MV cable as messenger-supported wiring is only permitted in industrial establishments under 396.10(B)

396.10(B) permits MV cable as messenger-supported wiring only in industrial establishments where qualified persons ensure proper maintenance and supervision. Outside that context, general use is limited to the cable types in Table 396.10(A) under 396.10(A), so a commercial retail building doesn't qualify under either provision.

Correct: B — When it complies with 225.4, 250.184(A), 250.184(B)(7), and 250.187(B)

396.30(B) permits the messenger to be used as a neutral conductor only where it meets 225.4, 250.184(A), 250.184(B)(7), and 250.187(B). Messenger material alone doesn't qualify it, a messenger can't simultaneously be the neutral and the EGC on the same system, and the code explicitly allows more than pure mechanical support when these sections are satisfied.

Correct: B — To eliminate tension on the conductors

396.30(A) requires the messenger to be supported at dead ends and intermediate locations so as to eliminate tension on the conductors — the messenger, not the conductors, carries the mechanical load. Ampacity derating and grounding paths are not addressed by this section.

Correct: D — 50 mm (2 in.)

398.19 requires at least 50 mm (2 in.) of separation from metal raceways, piping, or other conducting material, unless a continuous and firmly fixed nonconductor is used in addition to the conductor's insulation. The conductor's own insulation alone is not enough to eliminate the clearance requirement.

Correct: A — Protect the conductors with guard strips, a running board, boxing, or conduit

398.15(C) considers conductors within 2.1 m (7 ft) of the floor exposed to physical damage, so a run at 5 ft crossing a stud requires one of the listed protection methods. There is no 4 ft exemption, and wider spacing alone doesn't satisfy the rule.

Correct: B — Within 150 mm (6 in.)

398.30(A)(1) requires a support within 150 mm (6 in.) of a tap or splice. The 300 mm (12 in.) distance applies to dead-end connections at a lampholder or receptacle under 398.30(A)(2), not splices, and the 1.4 m figure is the maximum general interval spacing, not the splice rule.

Correct: A — Form drip loops on them

398.15(B) requires drip loops formed on conductors entering or leaving locations subject to dampness, wetness, or corrosive vapors. Splicing near the entry, taping the conductors, or derating ampacity are not the requirement this section imposes.

Correct: B — In dry locations not exposed to physical damage

398.15(A) permits flexible nonmetallic tubing to separately enclose open-wiring conductors only in dry locations not exposed to physical damage; wet locations and physical-damage exposure aren't covered by this allowance, regardless of the securing method used.

Correct: A — An agricultural establishment on a 480-volt system

398.10 limits open wiring on insulators to industrial or agricultural establishments on systems of 1000 volts or less. A 480-volt agricultural establishment qualifies. Dwellings, commercial offices, and commercial kitchens are not industrial or agricultural establishments, so they don't meet the use permitted in 398.10.

Correct: C — 9.0 m (30 ft)

398.30(C) permits supports up to 9.0 m (30 ft) apart for 250 kcmil and larger conductors run across open spaces in industrial establishments with qualified-persons maintenance. The 4.5 m (15 ft) option and 'no limit' option are not what this section states, and the standard smaller-conductor spacing is a different, shorter interval that doesn't apply once the exception's conditions are met.