Special Occupancies practice questions (Articles 518–590)

Correct: C — 518.5(C)

518.5(C) specifically addresses whether the neutral of a feeder supplying solid-state dimmer systems counts as current-carrying for ampacity adjustment, distinguishing phase-control from sine-wave dimming systems. 518.5(A)(1) instead covers overcurrent protection for power outlets/appliance centers, not neutral loading, and 518.4(A) covers general wiring methods, not conductor counting.

Correct: B — As part of the school's other occupancy, since it holds fewer than 100 persons and is incidental to the main use

Per 518.2(B), occupancy of a room for assembly purposes by less than 100 persons, incidental to the building's other occupancy, is classified as part of that other occupancy. Being listed in 518.2(A) doesn't override the occupant-load test in 518.2(B).

Correct: A — A listed power outlet with sufficient voltage and ampere rating for the load

518.5(B) requires portable switchboards and portable power distribution equipment to be supplied only from listed power outlets or listed commercial appliance outlet centers with sufficient voltage and ampere ratings — not just any panelboard, feeder tap, or compatible receptacle.

Correct: A — 590.6's GFCI requirements do not apply, but all other GFCI requirements of the Code still apply

518.3 specifically exempts exhibition hall temporary wiring from 590.6's GFCI requirements, but is explicit that all other GFCI requirements of the Code still apply. The idea that all GFCI rules are waived, or that only 590.6 applies, both invert this — 590.6 is the one exemption, not the surviving rule, and GFCI protection isn't optional under 518.3.

Correct: D — When encased in not less than 2 in. of concrete

518.4(A)(3) permits nonmetallic raceway only when encased in not less than 50 mm (2 in.) of concrete. Occupant load thresholds and ceiling location aren't the qualifying condition, and having an EGC alone doesn't exempt nonmetallic raceway from the concrete-encasement requirement — that requirement applies regardless of EGC type.

Correct: B — 167 percent

522.10(A)(2) caps overcurrent protection for non-transformer power-limited control power sources at 167% of the volt-ampere rating divided by rated voltage. The 125 percent figure is the cap for non-power-limited sources under 522.10(B)(2), not power-limited ones.

Correct: C — The equipment powered is functionally associated with the control circuit

522.24(B)(1) allows control and power circuits to share a cable, enclosure, or raceway only where the powered equipment is functionally associated with the control circuit. The common-voltage-insulation rule applies to two control circuits together under 522.24(A), not to control-with-power mixing.

Correct: A — 30 volts and 1000 volt-amperes

522.10(A) sets both limits together: not more than 30 volts and 1000 volt-amperes. A source at 50 volts, or one with no VA cap, or one rated at the 300-volt non-power-limited threshold does not meet the power-limited definition.

Correct: C — 522.5

522.5 caps control voltage at 150 volts nominal AC (or 300 volts DC) to ground, so a 277-volt AC control secondary fails this limit regardless of transformer construction. 522.10(A)(1) covers control transformer construction/listing requirements, not the voltage ceiling itself.

Correct: B — Table 522.22

Per 522.22, conductors 16 AWG and smaller use Table 522.22 for ampacity. A 20 AWG conductor falls in that range, so Table 522.22 applies, not the general conductor table (310.16) used for larger sizes per 522.23.

Correct: A — Extra-hard usage, or hard usage since it's not subject to physical damage

Per 525.20(A), flexible cords/cables must be listed for extra-hard usage, but where they are not subject to physical damage, hard usage is also permitted. Hard usage alone (without the physical-damage condition) and 'any cord' are not correct, and the extra-hard-usage-only choice ignores the explicit hard-usage allowance in the rule.

Correct: D — GFCI protection for personnel

525.23(A)(1) requires GFCI protection for all 125-volt, single-phase, 15- and 20-ampere non-locking receptacles used for disassembly and reassembly, regardless of indoor/outdoor location. AFCI is not the protection type this section addresses, and skipping protection ignores the rule entirely.

Correct: B — It must not create a greater tripping hazard than the uncovered cable

525.20(G) requires that matting or any other cable protection method not constitute a greater tripping hazard than the uncovered cables. It has no ampacity rating requirement, and 300.5 burial depths are explicitly stated not to apply.

Correct: B — Egress lighting must never be GFCI protected

525.23(C) states GFCI protection is not permitted for egress lighting, since a nuisance trip could leave an evacuation path dark. The other options invert or conditionally apply a requirement that the code flatly prohibits.

Correct: D — When the receptacle supplies a motor load permitted under Article 430

525.22(C) caps receptacle overcurrent protection at the receptacle's ampere rating, with the sole exception being motor loads permitted under Article 430. The feeder device rating, temporary lighting use, and single-pole connector use don't create an exception to this cap.

Correct: B — Within sight of and within 1.8 m (6 ft) of the operator's station

525.21(A) requires the disconnecting means to be located within sight of and within 1.8 m (6 ft) of the operator's station — both conditions apply together. A distance-only rule like 15 m (50 ft), a location tied to the distribution point instead of the operator, or an unspecified marked location all miss the specific sight-and-distance requirement.

Correct: B — 525.30

525.30 requires metal raceways, equipment enclosures, and metal frames of portable structures/trailers/trucks connected to the same source to be bonded together. 525.31 addresses grounding (connection to the grounding electrode/EGC system) rather than bonding equipment together, and 525.32 covers continuity assurance testing of the EGC, not the bonding requirement itself.

Correct: D — 525.31

525.31 specifically addresses connecting the equipment grounding conductor to the grounded conductor at the service disconnect or, for a separately derived system like a generator, at the generator or first disconnecting means. 525.30 covers bonding of equipment, not this grounded/grounding conductor connection point, and 525.32 addresses continuity assurance testing, not where the connection is made.

Correct: B — 525.6

525.6 is the general rule requiring mechanical protection for electrical equipment and wiring methods on portable structures wherever they're subject to physical damage. 525.10(A) only addresses guarding of services, and 525.20(H) covers boxes and fittings for wiring methods, not this general physical-damage protection requirement.

Correct: D — 15 ft in any direction, except for conductors supplying the portable structure

Per 525.5(B)(1), portable structures must stay 15 ft (4.5 m) from overhead conductors at 600 volts or less in any direction, except conductors that supply the structure itself. The no-exceptions and horizontal-only options describe the over-600-volt rule in 525.5(B)(2), not this one, and 10 ft is not the code distance.

Correct: A — In a separate room from the projection room

540.11(A) requires motor-generator sets, transformers, rectifiers, rheostats, and similar equipment to be located in a separate room where nitrate film is used. Simply grounding the equipment or placing it in the projection room without meeting the arc/spark and commutator-end conditions does not satisfy the rule.

Correct: C — 750 mm (30 in.)

540.12 requires clear working space not less than 750 mm (30 in.) wide on each side and at the rear of the equipment. The other dimensions are clearances used elsewhere in the NEC (like general equipment working space in Article 110), not the value specified for projection equipment.

Correct: D — Permanent construction approved for the type of building it's located in

540.10 requires every projection room to be of permanent construction and approved for the type of building in which it is located. It also specifically states such rooms are not classified as hazardous locations under Article 500, so the fire-rated/hazardous-classification option is a plausible-sounding but incorrect distractor.

Correct: D — A general-purpose receptacle circuit unrelated to projection or sound equipment

540.11(B) prohibits switches, overcurrent devices, or other equipment not normally required or used for projectors, sound reproduction, or special-effect lamps. Equipment tied to projector operation, sound reproduction, or special-effect lamps is exactly what the section permits.

Correct: B — All exposed metals likely to become energized

545.11 requires bonding/grounding provisions for all exposed metals likely to become energized, not a narrower subset limited to service equipment, weather exposure, or proximity to a receptacle.

Correct: B — The point of attachment is known prior to manufacture

545.6 allows pre-erection installation of service-entrance conductors only when the point of attachment is known prior to manufacture. There's no AHJ-variance exception, no conduit-type exception, and no ampacity threshold mentioned in this section.

Correct: D — Only at cabinets, boxes, or fittings

545.4(B) allows cable in closed construction to be secured only at cabinets, boxes, or fittings when conductors are 10 AWG or smaller and physical protection is provided — it does not require securing at regular intervals, at every framing member, or eliminate securing entirely.

Correct: B — Exactly one, in a readily accessible location

545.24(A) calls for a single disconnecting means for each relocatable structure. The six-disconnect grouping rule is a service-equipment concept from a different article and doesn't apply here, and splitting the disconnect by load type or by panelboard count both add disconnects beyond the one this section allows.

Correct: B — It must be tested, identified, and listed to applicable standards

545.10 permits a receptacle or switch with integral enclosure and mounting means where it is tested, identified, and listed to applicable standards. There's no separate requirement tying approval to a specific assembly stage, matching field enclosure types, or restricting installation to modules assembled after site placement.

Correct: A — 545.26

545.26 specifically requires exposed non-current-carrying metal parts likely to become energized to be bonded to the panelboard's grounding terminal or enclosure, with a bonding conductor run to an accessible chassis terminal. 545.27 instead covers intersystem bonding (grounding electrode bonding for communication/other systems), not chassis metal parts, so it doesn't apply here.

Correct: A — A common grounding electrode conductor and tap arrangement per 250.64(D)(1), using the 545.26 chassis bonding conductor as the tap conductor

545.22(D)(2) permits a common grounding electrode conductor with a tap arrangement per 250.64(D)(1) when structures are structurally joined into one unit, and specifically allows the 545.26 chassis bonding conductor to serve as that tap conductor. Fully independent electrode systems, omitting the GEC, or requiring each structure to keep its own separate tap all defeat the purpose of the shared arrangement this section permits.

Correct: A — It must simultaneously disconnect all ungrounded service conductors

547.41(A)(3) requires simultaneous disconnection of all ungrounded service conductors from the premises wiring — sequential or single-conductor switching would leave part of the system energized and doesn't satisfy the rule.

Correct: A — 210.8(B)

547.28 directs agricultural buildings to follow 210.8(B) for GFCI protection in areas not otherwise covered by the article. 210.8(A) covers dwelling units, not this scope, and 547.5 and 215.9 address unrelated topics.

Correct: D — They must be listed for wet locations, with weatherproof equipment enclosures

547.23 classifies periodically washed or sprayed surfaces as wet locations, not just damp — this requires boxes and conduit bodies listed for wet locations and weatherproof equipment enclosures, a stricter standard than the general damp/wet 'prevent moisture from entering' rule that applies to merely damp areas.

Correct: A — 547.26

547.26 specifically prohibits concealing nonmetallic cable in walls/ceilings of areas contiguous with livestock confinement areas due to rodent damage risk. 547.24 covers corrosive atmosphere protection and 547.23 covers damp/wet locations — neither addresses rodent-driven concealment restrictions; 547.20 sets general wiring method requirements but not this specific concealment ban.

Correct: A — Type NMC cable

547.20 lists Type NMC cable as a permitted wiring method. Type SE is permitted only in copper, not aluminum; Type MC must be jacketed to qualify; and ordinary Type NM (without corrosion resistance) is not on the list at all.

Correct: D — 547.41(B)(1)

547.41(B)(1) governs conductor sizing (per Article 220 Part V) when the disconnect and OCPD sit at the building rather than the distribution point; 547.41(A)(5) covers site-isolating device ratings and 547.42 covers the opposite arrangement where the disconnect stays at the distribution point, so neither addresses sizing supply conductors run to the building.

Correct: C — 8 AWG solid copper

Per 547.44(B), the bonding conductor must be solid copper, insulated, covered, or bare, and not smaller than 8 AWG. The 10 AWG option is undersized, the stranded-copper option fails the solid-conductor requirement, and aluminum is not permitted for this bonding conductor.

Correct: C — A concrete floor in a livestock confinement area with metallic equipment accessible to the animals that may become energized

547.44(A)(1) requires an equipotential plane indoors where there's a concrete floor in a confinement area and accessible metallic equipment that may become energized. The poultry-only building doesn't qualify because 547.44 excludes poultry from the definition of livestock. The dirt-floor pasture and the slab with no metallic equipment both lack a required element of the trigger.

Correct: A — Only buildings or areas meeting the excessive dust or corrosive atmosphere conditions of 547.1(A) or (B)

547.1 limits the article's scope to agricultural buildings, or parts/adjacent areas of similar nature, that meet the conditions specified in 547.1(A) or (B) — dust/dust-with-water or corrosive atmosphere. Simply being on agricultural property or housing livestock, without those conditions, isn't enough to bring a building under Article 547.

Correct: A — 200 mm (8 in.)

547.21 requires cables to be secured within 200 mm (8 in.) of each cabinet, box, or fitting. The other distances are not the figure specified in this section.

Correct: D — 547.29

547.29 covers switches, pushbuttons, and similar control devices and points to 547.22's enclosure requirements. 547.30 governs enclosures for motors themselves (rotating machinery), and 547.28 addresses GFCI protection, not enclosure type, so neither applies to a pushbutton station.

Correct: A — GFCI protection for personnel

590.6(B) permits either GFCI protection per 590.6(B)(1) or a full assured equipment grounding conductor program per 590.6(B)(2). An informal or undocumented check doesn't satisfy 590.6(B)(2), which requires a written, continuously enforced program, and a one-time end-of-project test doesn't meet the recurring testing schedule required.

Correct: A — Ground-fault circuit-interrupter protection for personnel

Under 590.6(A)(2), permanent receptacle outlets used for temporary electric power still require GFCI protection for personnel — being part of permanent wiring does not exempt them. The assured equipment grounding conductor program is a separate, narrow alternative limited to specific industrial situations under 590.6(A), and AFCI protection is not the requirement this section addresses.

Correct: B — With a fitting listed for connecting flexible cords or cables to boxes

590.4(I) requires a fitting listed for the purpose of connecting flexible cords/cables to boxes. Tape, knots, and mounting height are not substitutes for a listed fitting.

Correct: D — No — receptacles shall not be installed on any branch circuit that supplies temporary lighting

590.4(D)(1) states receptacles on construction sites shall not be installed on any branch circuit that supplies temporary lighting — this is a flat prohibition, not conditioned on GFCI protection, load level, or multiwire pole separation.

Correct: C — No — all branch circuits must originate in approved power outlets, switchgear, switchboards, panelboards, motor control centers, or fused switch enclosures

590.4(C) requires all branch circuits to originate in approved supply equipment such as a power outlet, switchgear, switchboard, panelboard, motor control center, or fused switch enclosure. Cord rating and the 150V-to-ground limit are separate requirements that apply to single insulated conductors under 590.3(B), not a substitute for proper origination.

Correct: B — A means to disconnect simultaneously all ungrounded conductors at the point of origin

590.4(E) requires multiwire branch circuits to have a means to disconnect all ungrounded conductors simultaneously at the power outlet or panelboard where the circuit originates. Separate single-pole switches without simultaneous operation don't meet this, disconnecting only the neutral is not what's required, and temporary circuits are not exempt.

Correct: D — It must be current limiting

277 V to ground exceeds 150 V, the system is 480 V phase-to-phase (not over 1000 V), and available fault current exceeds 10,000 A, so 590.8(B) requires a current-limiting device. There's no 600 V phase-to-phase carve-out, and an interrupting rating figure is a different requirement than current limiting.