11.6 Agricultural Buildings, Manufactured Homes, RV Parks and Marinas

Article 547 — Agricultural Buildings

547.1 Scope. Article 547 applies to agricultural buildings or that part of a building or adjacent areas of similar or like nature where excessive dust and dust with water may accumulate, including areas of confinement systems where litter dust, feed dust, or debris may accumulate; and where a corrosive atmosphere exists, including areas where poultry and animal excrement may cause corrosive vapors, corrosive particles may combine with water, the area is damp and wet by reason of periodic washing for cleaning and sanitizing, and similar wet or damp areas.

547.4 Wiring Methods. Types UF, NMC, copper SE cables, jacketed Type MC cable, rigid nonmetallic conduit, liquidtight flexible nonmetallic conduit, and other cables or raceways suitable for the location, with approved termination fittings, shall be the wiring methods employed.

547.5(F) Receptacles. All 125-volt, single-phase, 15- and 20-ampere general-purpose receptacles installed in the following locations shall have GFCI protection: (1) areas having an equipotential plane; (2) outdoors; (3) damp or wet locations; and (4) dirt confinement areas for livestock.

547.5(G) Luminaires. Luminaires shall comply with the following: (1) minimize the entrance of dust, foreign matter, moisture, and corrosive material; (2) where exposed to physical damage, be protected by a suitable guard; (3) where exposed to water from condensation, building cleansing water, or solution, be listed as suitable for wet locations.

547.9 Electrical Supply to Building(s) or Structure(s) from a Distribution Point. Where a distribution point supplies more than one building or structure, requirements apply for the site-isolating device, its accessibility, marking, and grounding.

547.10 Equipotential Planes and Bonding of Equipotential Planes.

• (A) Where Required. Equipotential planes shall be installed where required in (A)(1) and (A)(2): (1) Indoors — equipotential planes shall be installed in confinement areas with concrete floors where metallic equipment is located that may become energized and is accessible to animals; (2) Outdoors — equipotential planes shall be installed in concrete slabs where metallic equipment is located that may become energized and is accessible to animals. The equipotential plane shall encompass the area around the equipment where the animal stands while accessing the equipment.
• (B) Bonding. Equipotential planes shall be bonded to the electrical grounding system. The bonding conductor shall be solid copper, insulated, covered, or bare, and not smaller than 8 AWG. The means of bonding to wire mesh or conductive elements shall be by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means. Slatted floors that are supported by structures that are a part of an equipotential plane shall not require bonding.

The hazard being addressed is step and touch potential. Livestock are far more sensitive to small voltage gradients than people — a few volts between a metal waterer and a wet concrete floor is enough to make cattle refuse to drink, and larger gradients can be lethal. An equipotential plane ties the reinforcing mesh, metallic equipment, and grounding system together so no gradient can develop across the animal's stance.

Article 550 — Mobile Homes, Manufactured Homes, and Mobile Home Parks

550.4(A) Mobile Home Not Intended as a Dwelling Unit. A mobile home not intended as a dwelling unit — for example, one intended for office use — shall not be required to meet the provisions pertaining to the number or capacity of circuits required, but shall meet all other applicable requirements if provided with an electrical installation.

550.10 Power Supply. The power supply to the mobile home shall be a feeder assembly consisting of not more than one listed 50-ampere mobile home power-supply cord, or a permanently installed feeder.

550.10(B) Cord. The cord shall be permanently attached to the distribution panelboard or to a junction box permanently connected to the distribution panelboard, with the free end terminating in an attachment plug cap. The overall length of the cord, measured from the end of the cord, including bared leads, to the face of the attachment plug cap, shall not be less than 6.4 m (21 ft) and shall not exceed 11 m (36.5 ft). The length of the cord from the face of the attachment plug cap to the point where the cord enters the manufactured home shall not be less than 6.0 m (20 ft).

550.18 Calculations. The calculated load for determining the power supply shall be the sum of the lighting, small appliance, and laundry loads, plus specified appliance loads, using the method in 550.18(B).

550.32(A) Manufactured Home Service Equipment. The service equipment shall be located adjacent to the manufactured home and not mounted in or on the manufactured home. The service equipment shall be located in sight from and not more than 9.0 m (30 ft) from the exterior wall of the manufactured home it serves.

Exception: For manufactured homes, the service equipment shall be permitted to be installed in or on a manufactured home, provided all of the following conditions are met: (1) the manufacturer includes in its written installation instructions information indicating that the home shall be secured in place by an anchoring system or installed on and secured to a permanent foundation; (2) the installation of the service equipment complies with Part VII of Article 230; (3) means are provided for the connection of a grounding electrode conductor to the service equipment and routing it outside the structure; (4) upon installation of the feeder to the manufactured home, the grounding electrode conductor is connected to the grounding electrode system; and (5) the manufactured home is provided with the wiring and equipment required by this article.

550.33 Feeder. Feeder conductors shall comply with the following: the feeder shall consist of either a listed cord or a permanently installed feeder consisting of four continuous, insulated, color-coded conductors, one of which shall be identified by green with or without one or more yellow stripes for use as the equipment grounding conductor.

The four-wire feeder with isolated neutral at the manufactured home is the same principle as 250.32(B)(1) — the neutral-to-ground bond exists only at the service equipment adjacent to the unit.

Article 551 — Recreational Vehicles and RV Parks

551.71 Type Receptacles Provided. Every recreational vehicle site with electrical supply shall be equipped with at least one 20-ampere, 125-volt receptacle. A minimum of 20 percent of all RV sites, with electrical supply, shall each be equipped with a 50-ampere, 125/250-volt receptacle conforming to the configuration for a 50-ampere, 3-pole, 4-wire grounding-type receptacle. A minimum of 70 percent of all RV sites with electrical supply shall each be equipped with a 30-ampere, 125-volt receptacle. The remainder of all RV sites with electrical supply shall be equipped with one or more of the receptacle configurations specified.

551.71(F) Ground-Fault Circuit-Interrupter Protection. All 125-volt, single-phase, 15- and 20-ampere receptacles shall have listed GFCI protection for personnel.

551.73 Calculated Load. The calculated load of a feeder or service for an RV park shall be calculated on the basis of not less than: 12,000 volt-amperes per site equipped with a 50-ampere, 120/240-volt supply facility; 3,600 volt-amperes per site equipped with both 20-ampere and 30-ampere supply facilities; 2,400 volt-amperes per site equipped with only 20-ampere supply facilities; and 600 volt-amperes per site equipped with only 20-ampere supply facilities that are dedicated to tent sites. The demand factors in Table 551.73(A) may then be applied, ranging from 100 percent for 1 site down to 41 percent for 21 to 40 sites and lower for larger parks.

551.72 Distribution System. The recreational vehicle site supply equipment shall be located on the left side of the parked vehicle, on the road side, and not more than 2.1 m (7 ft) from the point of entrance of the vehicle.

Article 555 — Marinas, Boatyards, Floating Buildings, and Commercial and Noncommercial Docking Facilities

This article addresses electric shock drowning, a hazard specific to fresh water. Current leaking from a boat or dock wiring into fresh water creates a voltage gradient in the water. A swimmer in that gradient loses muscle control and drowns, often with no burn or mark. Because fresh water is a poorer conductor than the human body, the current preferentially takes the path through the swimmer.

555.9 Electrical Datum Plane Distances. The electrical datum plane is defined by reference to water level: in land areas subject to tidal fluctuation, a horizontal plane 60 cm (2 ft) above the highest tide level for the area occurring under normal circumstances; in land areas not subject to tidal fluctuation, a horizontal plane 60 cm (2 ft) above the highest water level for the area occurring under normal circumstances; and for floating structures and landing stages, a horizontal plane 76 cm (30 in.) above the water level at the floating structure or landing stage and a minimum of 30 cm (12 in.) above the level of the deck.

555.10 requires electrical connections to be located at least 305 mm (12 in.) above the deck of a floating pier and at least 12 inches above the deck of a fixed pier, but not below the electrical datum plane.

555.30 requires the service equipment for floating docks or marinas to be located adjacent to, but not on or in, the floating structure.

555.33 Receptacles. (A)(1) Shore power receptacles shall be of the locking and grounding type. (A)(2) Receptacles providing shore power shall be rated not less than 30 amperes. (A)(4) Receptacles shall be housed in a marine power outlet listed as marina power outlets or listed for wet locations.

555.35 Ground-Fault Protection.

• (A)(1) Receptacles Providing Shore Power. Outlets providing shore power for boats shall be protected by ground-fault protection of equipment not exceeding 30 milliamperes. Ground-fault protection of the feeder or branch circuit shall be permitted as a means of compliance.
• (A)(2) Receptacles Other Than Those Providing Shore Power. All receptacles other than those providing shore power, rated 125 volts, single phase, 15 and 20 amperes, shall be provided with GFCI protection for personnel.
• (A)(3) Feeder and Branch-Circuit Conductors. Feeder and branch-circuit conductors installed on docking facilities shall be provided with ground-fault protection not exceeding 100 milliamperes. Coordination with downstream ground-fault protection shall be permitted at the feeder overcurrent protective device.
• (B) Leakage Current Measurement Device. Marinas, boatyards, and docking facilities with more than one receptacle providing shore power for boats shall have a listed leakage current measurement device available on site to determine leakage current from each boat that will utilize the shore power receptacles.

555.34(A) Signage. Permanent safety signs shall be installed to give notice of electrical shock hazard risks to persons using or swimming near a boat dock or marina, stating "WARNING — POTENTIAL SHOCK HAZARD — ELECTRICAL CURRENTS MAY BE PRESENT IN THE WATER." The signs shall be located at each entry point of the docking facility, on the exterior of a marina, and at intervals not exceeding 30.5 m (100 ft) along the perimeter of the docking facility.

555.13 Wiring Methods and Installation requires portable power cables to be permitted only as flexible connections to floating structures, and specifies the raceway and cable types permitted.

Alaska Application

Alaska has a very large small-boat harbor system across Southeast, Southcentral, and the Aleutians, plus extensive freshwater float-plane and boat facilities on lakes and rivers. The 555.35 ground-fault requirements and the 555.34 signage requirements apply to those docking facilities. The electric-shock-drowning hazard is most acute in fresh water, but the corrosion environment in salt water makes leakage more likely to develop, and the 30-milliampere and 100-milliampere GFPE thresholds apply regardless.

Agricultural Article 547 rules apply to Alaska's livestock operations in the Matanuska-Susitna Valley, Delta Junction, and Kenai areas, and to reindeer and musk ox facilities. The equipotential plane requirement in 547.10 attaches to concrete-floored confinement areas with accessible metallic equipment, not to the species of animal.