10.3 Agricultural Buildings, Mobile Homes, RV Parks, Marinas & Temporary Installations (Articles 545-590)

Why this section matters

Articles 517 through 590 carry about four questions. Health care and assembly occupancies are in Section 10.2. This section covers the remaining occupancies most likely to appear: agricultural buildings (547), mobile and manufactured homes (550), RV parks (551), marinas and docking facilities (555), and temporary installations (590).

Agricultural buildings (Article 547)

Scope: agricultural buildings, or parts of them, where excessive dust or dust with water may accumulate (poultry, livestock, and fish confinement areas where litter or feed dust builds up), and where a corrosive atmosphere exists from poultry or animal excrement or from periodic washing.

Washington limit: Article 547 applies only when the building is larger than 1,000 square feet and used as part of a business or commercial farming activity (WAC 296-46B-547).

Wiring methods. Permitted methods include:

• Types UF, NMC, and copper SE cable;
• jacketed Type MC cable;
• rigid nonmetallic conduit and liquidtight flexible nonmetallic conduit;
• other cables and raceways suitable for the location, with approved fittings.

Type NM is not on the list for these areas. Boxes, fittings, and wiring devices must be dust-tight or weatherproof and corrosion resistant. Luminaires must minimize the entry of dust, water, and foreign material and be protected from damage by livestock.

GFCI: receptacles in the covered areas of agricultural buildings (damp or wet locations, dirt confinement areas for livestock, and outdoors) need GFCI protection as the article requires.

Equipotential planes:

• Where required: indoors, in livestock confinement areas with concrete floors where metallic equipment that livestock can reach may become energized; outdoors, in concrete slabs where metallic equipment is accessible to livestock and may become energized.
• Construction: wire mesh or other conductive elements embedded in or placed under the concrete.
• Bonding: connected to the electrical grounding system with a solid copper conductor, insulated, covered, or bare, not smaller than 8 AWG.
• Purpose: keep the animal's hooves and the metal it touches at the same potential. Cattle notice stray voltage of a volt or two, which is why the plane matters even when the voltage seems harmless.

Distribution point: farms fed from one service commonly use a site-isolating device at a central distribution point (a yard pole), with each building treated as a separate structure fed by a feeder.

Mobile homes, manufactured homes, and parks (Article 550)

Washington differences (WAC 296-46B-550):

• With a permanent feeder wiring method, the equipment grounding conductor may be bare; bare conductors used underground must be copper. A portable cord is not a permanent method.
• A service may be installed on the home only with the manufacturer's written instructions at the first inspection, or when installed at the factory.
• Every alteration needs a permit. Circuits leaving the home's own panel need a factory-assembled-structure (FAS) permit, and work beyond the junction box under the home needs a second permit.

Recreational vehicle parks (Article 551)

Receptacles at RV sites (551.71):

• every site with electrical supply: at least one 20 A, 125 V receptacle;
• at least 20 percent of sites: a 50 A, 125/250 V receptacle;
• at least 70 percent of sites: a 30 A, 125 V receptacle.

Calculated load per site (551.73(A)): 9,600 VA for 50 A sites, 3,600 VA for 20 A and 30 A sites, and 2,400 VA for sites with only a 20 A supply. The demand factors of Table 551.73(A) then apply, based on the number of sites.

Marinas, boatyards, and docking facilities (Article 555)

Water turns a small ground fault into a drowning hazard (electric shock drowning), so this article is strict.

Washington amendments (WAC 296-46B-555):

• Shore-power receptacles must be at least 20 A, single outlet, locking and grounding or pin-and-sleeve type.
• A floating building's supply overcurrent devices need ground-fault protection of 30 mA or less.
• "Adjacent" means within sight.
• Extra-hard-usage portable power cable may be used as permanent wiring under or within docks.

Temporary installations (Article 590)

Time limits (590.3):

• construction, remodeling, maintenance, repair, or demolition: for the length of the project;
• holiday decorative lighting: no more than 90 days;
• emergencies, tests, experiments, and developmental work: as needed.

Temporary wiring must be removed when the project or purpose is complete.

Wiring (590.4):

• Feeders and branch circuits may use cable assemblies, or cords and cables of the types in Table 400.4, within the limits of 590.4(B) and (C).
• Receptacles on construction sites may not be on the same branch circuit as temporary lighting (590.4(D)).
• Cables and cords must be protected from damage and supported. Vegetation may not support overhead spans, except festoon lighting, holiday lighting, and similar with strain relief.
• Washington requires a box for every splice in temporary wiring and treats every construction circuit as temporary (WAC 296-46B-590).

GFCI for personnel (590.6):

• (A)(1) Receptacles not part of the permanent wiring: all 125 V, single-phase, 15 A, 20 A, and 30 A receptacle outlets used by personnel need GFCI protection.
• (A)(2) Permanent receptacles used for temporary power: also GFCI protected. Listed cord sets or devices with GFCI protection meet the rule.
• (B) Other receptacles (for example, 250 V or three-phase): GFCI protection, or a written assured equipment grounding conductor program that includes regular testing and a designated person.

Washington also requires a temporary construction service to be disconnected once the permanent service is connected, unless L&I grants an extension (WAC 296-46B-590).