14.4 RV Parks (Article 551), Floating Buildings (Article 553) & Marinas/Docking Facilities (Article 555)
Key Takeaways
- NEC 551.71 requires every RV site with electrical supply to have at least one 20-ampere, 125-volt receptacle, with a minimum of 20 percent of sites equipped with a 50-ampere, 125/250-volt receptacle and a minimum of 70 percent equipped with a 30-ampere, 125-volt receptacle.
- RV park service and feeder loads are calculated at 9600 volt-amperes per 50-ampere site, 3600 volt-amperes per 30-ampere site, and 2400 volt-amperes per 20-ampere site, before the demand factors of Table 551.73(A) are applied.
- NEC 553.4 requires the service equipment for a floating building to be located adjacent to, but not in or on, the building or any floating structure.
- NEC 555.35 requires feeders on docking facilities to have listed ground-fault protection of equipment rated not more than 100 milliamperes, and shore power receptacles to be protected by GFPE set at not more than 30 milliamperes.
- The electrical datum plane for floating piers is 30 inches above the water level and at least 12 inches above the deck, and in land areas subject to tidal fluctuation it is 2 feet above the highest high tide for the area.
14.4 RV Parks (Article 551), Floating Buildings (Article 553) & Marinas/Docking Facilities (Article 555)
Section 13.4 covered agricultural buildings (Article 547) and manufactured and mobile homes (Article 550). The Special Occupancies subject area also lists mobile home parks, RVs and RV parks and, separately, floating buildings. Those are Articles 551, 553, and — because a floating building is almost always at a docking facility — 555.
1. Article 551 Part VI — Recreational Vehicle Parks
Article 551 has two halves. Parts I through V cover the vehicle itself — its low-voltage system, its generator, its power-supply assembly, and its factory wiring. Part VI is the part a journeyman installs: the park.
The receptacle mix (551.71)
| Requirement | Value |
|---|---|
| Every RV site with electrical supply | At least one 20-ampere, 125-volt receptacle |
| Minimum share of sites with a 50-ampere, 125/250-volt receptacle | 20 percent |
| Minimum share of sites with a 30-ampere, 125-volt receptacle | 70 percent |
| Remaining sites | One or more of the receptacle configurations conforming to 551.81 |
| GFCI | 125-volt, 15- and 20-ampere receptacles at RV sites require GFCI protection; the 30- and 50-ampere RV supply receptacles do not |
The percentages overlap deliberately — a single premium site may carry a 50-ampere, a 30-ampere, and a 20-ampere receptacle. An informational note in the Code observes that the 20 percent figure for 50-ampere sites can be inadequate for seasonal parks serving a high proportion of large coaches, so designers routinely exceed it.
Calculated load (551.73)
Each site type is assigned a volt-ampere value before demand factors:
| Site equipment | Calculated load per site |
|---|---|
| 50-ampere, 125/250-volt | 9,600 VA |
| 30-ampere, 125-volt | 3,600 VA |
| 20-ampere, 125-volt | 2,400 VA |
The total is then reduced by the demand factors of Table 551.73(A), which fall steeply as the site count rises because RVs do not all run air conditioning, water heaters, and converters at the same instant. Park distribution is normally a 120/240-volt, three-wire system (551.72).
Site supply equipment (551.77)
- Site supply equipment is located on the left (road) side of the parked RV, positioned at or near the rear of the stand, so that a coach parked in the normal orientation has its inlet within reach of the pedestal.
- The disconnecting means must be readily accessible and mounted within a defined height band above grade — not less than 2 feet and not more than about 6½ feet.
- Where the pedestal serves more than one site, the working space and the identification of which receptacle serves which site must be maintained.
- Overhead conductors crossing the park must maintain the clearances of 551.79 over the RV stands and the roadways.
2. Article 553 — Floating Buildings
A floating building is a building unit that floats on water, is moored in a permanent location, and has a premises wiring system served through connection by permanent wiring to an electricity supply on shore. That definition is what separates Article 553 from Article 555 (the docking facility) and from a boat (which is not covered by the NEC at all).
| Rule | Requirement |
|---|---|
| Service conductors and equipment (553.4) | The service equipment must be located adjacent to, but not in or on, the floating building or any floating structure — the disconnect stays on land where a firefighter can reach it |
| Number of supplies | Each floating building is served by a single set of feeder or service conductors, run from the shore service equipment out to the unit |
| Grounded conductor | The grounded (neutral) conductor must be insulated and identified, and it may not be connected to the equipment grounding conductor or to metal parts on the load side of the service disconnecting means |
| Equipment grounding | An insulated equipment grounding conductor must be run with the supply conductors from the shore service equipment to the floating building, and it — not the water, not the mooring hardware — is the fault-current return path |
| Bonding (553.11) | Metal parts of the floating structure, metal piping, and non-current-carrying metal enclosures must be bonded to the equipment grounding conductor |
[!WARNING] Why the neutral-to-ground separation matters here more than anywhere else. On land, a neutral-ground bond downstream of the service creates parallel current paths through metal. On the water, those parallel paths are through the water itself, and the resulting voltage gradient produces electric shock drowning — a swimmer paralyzed by current well below what would trip an ordinary overcurrent device. Every rule in Articles 553 and 555 about insulated neutrals, insulated equipment grounding conductors, and low-threshold ground-fault protection exists for that one failure mode.
3. Article 555 — Marinas, Boatyards, and Docking Facilities
The electrical datum plane
Article 555 begins with a reference plane rather than a rule: electrical equipment and connections must be above the electrical datum plane.
| Situation | Electrical datum plane |
|---|---|
| Floating piers | 30 inches above the water level and not less than 12 inches above the deck |
| Land areas subject to tidal fluctuation | 2 feet above the highest high tide for the area |
| Land areas not subject to tidal fluctuation | Referenced to the highest water level for the area under normal circumstances |
Ground-fault protection thresholds (555.35)
| Circuit | Required protection |
|---|---|
| Feeders installed on docking facilities | Listed GFPE rated not more than 100 mA |
| Shore power receptacles (the boat supply outlets) | GFPE set at not more than 30 mA |
| 15- and 20-ampere, 125-volt receptacles other than shore power | GFCI protection for personnel (Class A, 4–6 mA) |
The tiered thresholds reflect what each device protects: a Class A GFCI protects a person touching a tool on the dock, the 30 mA shore-power GFPE limits the leakage a boat can put into the water, and the 100 mA feeder GFPE catches a failing dock feeder without shutting down the entire marina every time a single boat leaks.
Leakage current measurement. The 2023 NEC requires docking facilities with multiple shore power receptacles to have a means of measuring leakage current so an individual leaking boat can be identified rather than the whole dock being de-energized. The listing requirement for the leakage current measurement device becomes effective January 1, 2026.
Equipment grounding conductors (555.37)
Equipment grounding conductors serving docking facilities must be insulated, wire-type conductors sized in accordance with 250.122 but not smaller than 12 AWG. The insulated requirement is deliberate: a bare or raceway-only grounding path in a saltwater environment corrodes to a high-resistance connection that will not clear a fault but will happily energize the water.
Other rules that produce exam items
- Wiring methods on piers include rigid metal conduit, IMC, Type PVC, Type RTRC, and liquidtight flexible conduits, with portable power cables permitted for the flexible connections that a floating pier requires.
- Disconnecting means for shore power connections must be readily accessible, located not more than 30 inches from the receptacle it controls, and must open all ungrounded conductors.
- Signage warning of the shock hazard of swimming near a docking facility is required where electrical equipment is installed.
- Overhead conductors are prohibited over the areas where boats are moored, launched, or moved by mast or boom.
An RV park is being designed with 60 sites, all with electrical supply. What is the minimum receptacle provision required by NEC 551.71?
A marina installs a new dock feeder serving twelve shore power pedestals, each with a 30-ampere, 125-volt shore power receptacle and one 20-ampere, 125-volt convenience receptacle. Which protection scheme complies with NEC 555.35?
A restaurant is built as a floating building moored permanently at a commercial dock and supplied by permanent wiring from shore. Where must the service equipment be located, and how is the grounded conductor treated?
What is the electrical datum plane for equipment installed on a floating pier at a freshwater marina?
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