Audio Equipment practice questions

Correct: B — The amplifier is listed and marked for use with that specific class of wiring method

Per 640.9(C), Class 1, 2, or 3 wiring is only permitted where the amplifier is listed and marked for use with that specific class of wiring method — the listing is what confirms the output energy matches that class's shock and fire risk. Current level, occupancy type, and add-on overcurrent protection aren't what qualifies the circuit; overcurrent protection is required but may already be inherent to the amplifier.

Correct: C — Cable ties designed and installed so they do not damage the cable

640.6(A) permits straps, staples, cable ties, hangers, or similar fittings, provided they don't damage the cable. Resting cable unsecured on a ceiling grid isn't a listed support method, and attaching it to a sprinkler pipe violates 300.11(A), which prohibits using another system's raceway or piping for support.

Correct: B — Whenever they are grouped or bundled in close physical contact within the same raceway, enclosure, or portable cord or cable

640.8 triggers on physical bundling in close contact within a shared raceway, enclosure, or cord/cable, regardless of voltage level or circuit classification. The 50-volt threshold and the Class 2 power-limited framing are unrelated conditions, and portable cords are explicitly included, not exempt.

Correct: A — It must comply with 647.6

640.7(B) specifically requires that grounding of separately derived systems with 60 volts to ground follow 647.6, rather than relying on general separately derived system bonding assumptions or receptacle wiring alone.

Correct: D — No closer than 1.5 m (5 ft) horizontally

640.10(A) sets the horizontal clearance at 1.5 m (5 ft) from the inside wall of a pool, spa, hot tub, or fountain for branch-circuit-powered audio equipment. The 3 ft and 10 ft options are both wrong distances, and GFCI protection is an additional requirement, not a substitute for the clearance.

Correct: A — 300.22(C)

640.3(B) applies 300.22(C) to other spaces used for environmental air (plenums), while 300.22(B) is specifically for ducts fabricated for environmental air — a different space. 392 Part II governs cable trays, and 722.135(E) covers communications cable substitution, neither of which is the plenum rule being tested here.

Correct: C — Chapters 1 through 4, except as modified by Article 640

Per 640.9(A)(1), wiring and equipment from the source of power to and between devices connected to the premises wiring system must comply with Chapters 1 through 4, except as modified by Article 640. Article 725 Part II applies only to wiring not connected to premises wiring or a system derived from it, per 640.9(A)(3), and Article 647 addresses only separately derived systems, per 640.9(A)(2).

Correct: A — 640.43

640.43 explicitly requires metal equipment racks to be bonded and grounded and also covers access and strain relief for rack wiring. 640.22 covers wiring methods used within racks/enclosures generally, not the bonding requirement, and 640.46 addresses access to the equipment room/space rather than the rack structure itself.

Correct: A — Listed as suitable for wet locations and sunlight resistant

640.42(E) requires extra-hard usage cords or cables for portable rack supply, and for outdoor portable or temporary use they must additionally be listed suitable for wet locations and sunlight resistant. Hard usage (not extra-hard) doesn't meet the base requirement, Article 725 Part III applies to loudspeaker/inter-equipment signal wiring under 640.42(B) and (C), and 640.42(D) covers non-branch-circuit power supplies like batteries, not portable rack feeds.

Correct: C — It is prohibited — loudspeaker/amplifier connectors cannot be compatible with nonlocking 15- or 20-ampere branch-circuit connectors

640.41 explicitly bars AC or DC loudspeaker/amplifier multipole connectors from being compatible with nonlocking 15- or 20-ampere branch-circuit connectors (or with 250-volt-or-greater connectors of either type). Amperage rating and polarization compliance don't override this prohibition, and the ban applies to both AC and DC.

Correct: C — When the rack is connected to a technical power ground

640.22 states bonding is not required if the rack is connected to a technical power ground. A locked room, low-voltage signal gear, or an insulated floor have no bearing on this exception.

Correct: D — 640.6(B)

640.6(B) is the specific rule requiring removal of the accessible portion of abandoned audio distribution cable. 640.6(C) instead covers cable that is being kept and identified for future use, and 640.3(B) deals with cable routed through ducts and plenums, not abandonment.

Correct: C — In compliance with Article 725

640.9(B) requires equipment with a separate auxiliary power supply input to be wired in compliance with Article 725. Treating it as an ordinary Article 640 primary feed, a communications circuit, or purely a grounding matter misses the specific cross-reference this section makes.

Correct: C — No, because the cable accumulation prevents removal of the access panel

640.5 specifically names suspended ceiling panels as access panels that must not be blocked by an accumulation of wires and cables. The coil resting on the panel would prevent its removal, so it violates the rule regardless of amplifier size — 640.5 has no power threshold.