15.4 Other Specific Occupancies — A Survey

Why These Occupancies Appear on the Exam

Area 9 is titled "Special Occupancies/Equipment/Conditions," and the outline spreads questions across several Chapter 5 articles. You will not see deep calculations here — only threshold numbers and the one or two rules that distinguish each occupancy. Texas in particular tests marinas/boatyards (Gulf coast) and manufactured/mobile homes (common statewide).

Survey of Key Occupancies

Notes on the Survey

• 518 vs 520: Theatrical areas inside an assembly occupancy are cross-referenced from 518.2(C) to Article 520. Article 520 governs fixed stage lighting (520.5), stage switchboards, and portable stage equipment. The 100-person threshold in 518.2 is the gating number for Article 518 applicability.
• 547 agricultural: Equipotential planes under 547.44 are required in indoor confinement areas with concrete floors and outdoors where livestock may contact metallic equipment. The plane is bonded to the grounding electrode system (unlike pool bonding under 680.26, which does not require connection to the grounding electrode). 547.28 requires GFCI for 125 V, 15/20 A receptacles in damp/wet locations — except in areas that require an equipotential plane.
• 555 marinas: The 30 mA shore-power threshold comes from ABYC research on preventing electric-shock drowning while minimizing nuisance trips. A leakage-current measurement device is required where more than three receptacles supply shore power. These rules are directly relevant along the Texas Gulf coast and around inland marinas.
• 550 manufactured/mobile homes: The 4-wire feeder is the most tested fact. The neutral bar in the home panel must be isolated (bonding screw removed); the EGC bus is bonded to the enclosure. Ranges, dryers, and cooking units must use 4-conductor cords — no bonded-neutral 3-wire connections. A bare EGC inside a cable assembly does not satisfy the "four insulated conductors" rule.
• 590 temporary wiring: The 90-day limit applies only to decorative/holiday lighting. Construction, remodeling, and demolition temporary wiring has no fixed time limit (590.3(A)); emergency/test/experimental wiring is permitted for the duration necessary (590.3(C)). All temporary wiring must be removed immediately upon completion of its purpose (590.3(D)). Wiring methods for temporary installations are covered in 590.4.

Deeper Detail on High-Value Articles

Article 518 - Assembly Occupancies (100 or more persons)

Article 518 applies to buildings or portions of buildings designed for 100 or more persons - theaters, churches, schools, restaurants, gymnasiums, and exhibition halls. The 100-person threshold in 518.2 is the gating number. Article 518 restricts wiring methods per 518.4 to those approved for the building construction type - generally metal raceways (RMC, IMC, EMT), MC, or MI cable for noncombustible construction. NM cable is not a permitted wiring method in assembly occupancies except where specifically allowed by 518.4 exceptions. Fixed stage lighting inside an assembly occupancy crosses over to Article 520 per 518.2(C).

Article 520 - Theaters and Similar Locations

Article 520 governs the theatrical areas within assembly occupancies - stages, dressing rooms, orchestra pits, and projection booths. The most-tested facts: fixed stage lighting wiring (520.5) must use metal raceways, MC, or MI cable; portable stage equipment uses listed stage cables that include an equipment grounding conductor; and stage dimmers must be listed and rated for the connected load. A 3-wire portable stage cable without an equipment grounding conductor is not permitted for portable stage equipment. The exam typically tests the metal raceway or MC requirement for fixed stage wiring and the conductor arrangement of portable stage cable.

Article 547 - Agricultural Buildings

The 547.44 equipotential plane rule applies in indoor livestock confinement areas and in outdoor areas where livestock may contact exposed non-current-carrying metal. The 547.2 definition of livestock excludes poultry - a tested distinction. The bonding conductor to the grounding electrode system must be at least 8 AWG solid copper. Wiring methods in agricultural buildings (547.5) must resist corrosion and moisture - RMC, PVC, LFNC, or jacketed MC listed for the location. Receptacles in damp or wet locations require GFCI per 547.28, except in areas that already require an equipotential plane, since the plane itself reduces the shock hazard.

Article 555 - Marinas and Boatyards (Texas Gulf Coast)

Article 555 is heavily tested in Texas because of Gulf coast marinas and inland reservoir docks. The core thresholds, all from 555.35, are easy to confuse: feeder GFPE is set to trip at no more than 100 mA; shore-power receptacle GFPE trips at no more than 30 mA (the ABYC threshold to prevent electric-shock drowning while limiting nuisance trips); and GFCI (Class A, 5 mA trip) is required for receptacles rated 60 A or less at 1-phase, or 100 A or less at 3-phase, at 150 V to ground or less. Article 555.3 also limits the shore-power supply voltage to ground to 150 V unless the marina supplies only documented 3-phase 480Y/277V or 600Y/346V systems. Receptacles must be mounted above the deck and above the electrical datum water line per Article 555. Worked scenario: A marina dock pedestal supplies a 30 A, 125 V shore-power receptacle. The receptacle needs GFPE at no more than 30 mA and GFCI at 5 mA, while the feeder conductor feeding the dock panel needs GFPE at no more than 100 mA. Candidates routinely swap the 30 mA receptacle trip and the 100 mA feeder trip.

Article 550 - Manufactured and Mobile Homes

The 4-wire feeder under 550.33 is the headline rule: two ungrounded conductors, a neutral, and an insulated equipment grounding conductor, minimum 100 A. At the home distribution panel the neutral is isolated from the enclosure (bonding screw removed) and the EGC bus is bonded to the enclosure. Three-wire bonded-neutral connections, which are common for ranges and dryers in site-built dwellings, are prohibited in manufactured and mobile homes - 4-conductor cords are required. A bare equipment grounding conductor inside a cable assembly does not satisfy the four insulated conductors rule. The feeder location follows 550.32 (under the home or in an approved raceway).

Article 590 - Temporary Installations

The key distinction is which 590.3 subsection governs: decorative and holiday lighting (590.3(B)) is capped at 90 days; construction, remodeling, and demolition wiring (590.3(A)) has no fixed limit and runs for the duration of the work; emergency, testing, and experimental wiring (590.3(C)) runs for the duration necessary. All temporary wiring must be removed immediately upon completion of its purpose (590.3(D)). Wiring methods for temporary installations (590.4) depend on voltage: listed portable power cable for circuits over 600 V, and listed cord sets or cables as permitted for 600 V and below. GFCI protection is required on all 125 V, 15 A and 20 A receptacles used for temporary construction per 590.6(A) - a heavily cited rule on OSHA-style questions.

Common Traps

Miscellaneous Equipment — Chapter 6 Grab Bag

The PSI outline closes Area 9 with Miscellaneous Equipment, which is where the Chapter 6 special-equipment articles that do not fit anywhere else land. Four carry recognizable exam numbers.

Two of these connect back to earlier chapters:

• 220.14(F) requires the sign load to be calculated at a minimum of 1,200 VA for each branch circuit required by 600.5(A) — that number shows up inside commercial service calculations.
• 240.4(D) small-conductor limits do not apply to welders, motors, or air-conditioning equipment; those use their own article, which is why a 630 welder can legitimately be on conductors that look undersized against the 15/20/30 A table.