9.4 Places of Assembly, Marinas & RV Parks

9.4 Places of Assembly, Marinas & RV Parks

Quick Reference: Special occupancies involving large gatherings of the public or hazardous aquatic/outdoor environments demand rigorous application of specialized NEC articles. NEC Article 518 (Places of Assembly) governs buildings with occupant loads of 100 or more persons, restricting wiring methods to metallic raceways and Type MC cable while barring nonmetallic systems unless concealed in 1-hour fire-rated assemblies. NEC Article 555 (Marinas & Boatyards) focuses on eliminating Electric Shock Drowning (ESD) through strict Ground-Fault Protection of Equipment (GFPE) thresholds (<= 30 mA shore power, <= 100 mA feeders) and Table 555.33(A) feeder demand factors. Finally, NEC Article 551 (RV Parks) mandates specific site receptacle configurations (20A GFCI, 30A, 50A) and electrical service sizing using Table 551.73(A) demand factors.

1. Places of Assembly (NEC Article 518)

Scope & Occupant Load Threshold (NEC 518.1 & 518.2)

NEC Article 518 applies to all buildings or portions of buildings designed or intended for the gathering together of 100 or more persons for civic, political, religious, educational, social, dining, recreational, or exhibition purposes.

• Qualifying Facilities: Auditoriums, banquet halls, restaurants, churches, exhibition halls, gymnasiums, conference centers, sports arenas, and museums.
• Calculation of Occupant Load: Determined using occupant density tables in the prevailing building code (e.g., IBC Chapter 10 / NFPA 101).

+---------------------------------------------------------------------------------------------------+
|                         PLACES OF ASSEMBLY WIRING METHODS (NEC 518.4)                             |
+-----------------------------------+---------------------------------------------------------------+
| APPROVED WIRING METHODS (518.4(A))| RESTRICTIONS & 1-HOUR FIRE-RATED EXCEPTIONS (518.4(B))        |
+-----------------------------------+---------------------------------------------------------------+
| • Rigid Metal Conduit (RMC)       | **Nonmetallic Wiring Methods Generally PROHIBITED:**          |
| • Intermediate Metal Conduit (IMC)| Nonmetallic-sheathed cable (Type NM/Romex), Electrical        |
| • Electrical Metallic Tubing (EMT)| Nonmetallic Tubing (ENT), and Rigid PVC Conduit are prohibited|
| • Flexible Metal Conduit (FMC)    | in places of assembly, **EXCEPT:**                            |
| • Liquidtight Flexible Metal (LFMC)| 1. Permitted in spaces/walls protected by a thermal barrier  |
| • Metal Clad Cable (Type MC)      |    having a **minimum 1-hour fire-resistance rating**.        |
| • Mineral-Insulated (Type MI)     | 2. Rigid Nonmetallic Conduit (PVC) is permitted if embedded in|
|                                   |    not less than **2 inches (50 mm) of solid concrete**.      |
+-----------------------------------+---------------------------------------------------------------+

+---------------------------------------------------------------------------------------------------+
|               PLACES OF ASSEMBLY: 1-HOUR FIRE RATING BOUNDARY RULE                                |
+---------------------------------------------------------------------------------------------------+
|   STANDARD UNRATED WALL / CEILING        |   1-HOUR FIRE-RATED WALL / CEILING ASSEMBLY            |
|                                          |                                                    |
|  [ Type NM Cable (Romex) ] ==> VIOLATION!|  [ Type NM Cable (Romex) ] ==> PERMITTED!          |
|  [ Rigid PVC Conduit ]    ==> VIOLATION!|  [ ENT / Rigid PVC ]       ==> PERMITTED!          |
|                                          |                                                    |
|  [ EMT / RMC / Type MC ]  ==> PERMITTED! |  [ EMT / RMC / Type MC ]   ==> PERMITTED!          |
+------------------------------------------+----------------------------------------------------+

2. Marinas, Boatyards & Commercial Docks (NEC Article 555)

Water and electricity create extreme shock hazards. In freshwater marinas, a leakage current as small as 100 mA into the water creates an electric field that paralyzes a swimmer's skeletal muscles, resulting in Electric Shock Drowning (ESD).

Ground-Fault Protection of Equipment (GFPE) (NEC 555.35)

To eliminate lethal stray currents, the NEC establishes strict ground-fault trip levels:

+---------------------------------------------------------------------------------------------------+
|                         MARINA GROUND-FAULT PROTECTION LEVELS (NEC 555.35)                        |
+-----------------------+-----------------------+---------------------------------------------------+
| CIRCUIT TYPE          | MAX TRIP LEVEL (GFPE) | DESIGN & COORDINATION REQUIREMENTS                |
+-----------------------+-----------------------+---------------------------------------------------+
| **Shore Power**       | **<= 30 mA**          | Every receptacle providing shore power to boats   |
| **Receptacles**       | (Equipment Protection)| must have ground-fault protection not exceeding   |
| (555.35(A)(1))        |                       | **30 milliamperes**.                              |
+-----------------------+-----------------------+---------------------------------------------------+
| **15A & 20A 125V**    | **4 mA to 6 mA**      | Standard convenience receptacles on docks must have|
| **General Outlets**   | (Class A GFCI)        | standard **Class A GFCI protection for personnel**.|
+-----------------------+-----------------------+---------------------------------------------------+
| **Distribution**      | **<= 100 mA**         | Feeders supplying marina distribution panels or   |
| **Feeders**           | (Feeder Protection)   | multiple pedestals must have GFPE not exceeding   |
| (555.35(B))           |                       | **100 mA**, with time delay for coordination.     |
+-----------------------+-----------------------+---------------------------------------------------+

Marina Feeder & Service Demand Factors (NEC Table 555.33(A))

When calculating the electrical service or feeder capacity for a marina dock, designers apply demand factors based on the total quantity of shore power receptacles:

+---------------------------------------------------------------------------------------------------+
|              NEC TABLE 555.33(A) MARINA SHORE POWER DEMAND FACTORS MATRIX                         |
+-----------------------------------+---------------------------------------------------------------+
| NUMBER OF SHORE POWER RECEPTACLES | DEMAND FACTOR (PERCENTAGE OF CONNECTED LOAD)                  |
+-----------------------------------+---------------------------------------------------------------+
| **1 to 4 Receptacles**            | **100%**                                                      |
| **5 to 8 Receptacles**            | **90%**                                                       |
| **9 to 14 Receptacles**           | **80%**                                                       |
| **15 to 30 Receptacles**          | **70%**                                                       |
| **31 to 40 Receptacles**          | **60%**                                                       |
| **41 to 50 Receptacles**          | **50%**                                                       |
| **51 to 70 Receptacles**          | **40%**                                                       |
| **71 or More Receptacles**        | **30%**                                                       |
+-----------------------------------+---------------------------------------------------------------+

Equipotential Bonding and Grounding (NEC 555.13 & 555.37)

• Insulated Equipment Grounding Conductor: An insulated copper equipment grounding conductor (minimum 12 AWG Cu) must be installed in all raceways serving dock circuits.
• Bonding of Metallic Parts (555.13): All metallic floating docks, structural metal pilings, metal raceways, pedestals, and transformer enclosures must be bonded together into an equipotential grounding grid connected to the electrical service grounding electrode system.

3. Recreational Vehicle (RV) Parks & Campgrounds (NEC Article 551)

Site Receptacle Requirements (NEC 551.71)

Every recreational vehicle park site equipped with electrical power must provide specific receptacle configurations to accommodate various vehicle classes (Class A motorhomes, fifth-wheels, travel trailers, pop-up campers):

+---------------------------------------------------------------------------------------------------+
|                         RV PARK SITE RECEPTACLE PROVISIONS (NEC 551.71)                           |
+-----------------------+-----------------------+---------------------------------------------------+
| RECEPTACLE TYPE       | MINIMUM PERCENTAGE    | RECEPTACLE CONFIGURATION & VOLTAGE RATING         |
+-----------------------+-----------------------+---------------------------------------------------+
| **20-Ampere 125V**    | **100% of Sites**     | NEMA 5-20R Duplex Receptacle with listed          |
| (551.71(A))           | (All Powered Sites)   | **Class A GFCI Protection**.                      |
+-----------------------+-----------------------+---------------------------------------------------+
| **30-Ampere 125V**    | **>= 70% of Sites**   | NEMA TT-30R (2-pole, 3-wire grounding, 125V)      |
| (551.71(B))           |                       | dedicated travel trailer receptacle.              |
+-----------------------+-----------------------+---------------------------------------------------+
| **50-Ampere 120/240V**| **>= 20% of Sites**   | NEMA 14-50R (3-pole, 4-wire grounding, 120/240V)  |
| (551.71(C))           | (Modern park minimum) | large motorhome / luxury coach receptacle.        |
+-----------------------+-----------------------+---------------------------------------------------+

RV Park Feeder & Service Load Calculations (NEC Table 551.73(A))

Under NEC 551.73(A), electrical loads for RV sites are calculated using the following statutory volt-ampere values per site pedestal:

• Sites with 50A, 30A, and 20A receptacles: 9,600 VA (or 12,000 VA where specified for high-demand coaches).
• Sites with 30A and 20A receptacles: 3,600 VA.
• Sites with 20A only receptacles: 2,400 VA.

+---------------------------------------------------------------------------------------------------+
|              NEC TABLE 551.73(A) RV PARK ELECTRICAL DEMAND FACTORS                                |
+-----------------------------------+---------------------------------------------------------------+
| NUMBER OF RECREATIONAL VEHICLE    | DEMAND FACTOR (PERCENTAGE OF CONNECTED CALCULATED LOAD)       |
| SITES SERVED BY FEEDER / SERVICE  |                                                               |
+-----------------------------------+---------------------------------------------------------------+
| **1 to 3 Sites**                  | **100%**                                                      |
| **4 Sites**                       | **86%**                                                       |
| **5 Sites**                       | **76%**                                                       |
| **6 Sites**                       | **72%**                                                       |
| **7 to 9 Sites**                  | **68%**                                                       |
| **10 to 12 Sites**                | **62%**                                                       |
| **13 to 15 Sites**                | **59%**                                                       |
| **16 to 18 Sites**                | **55%**                                                       |
| **19 to 21 Sites**                | **52%**                                                       |
| **22 to 40 Sites**                | **45%**                                                       |
| **41 to 60 Sites**                | **40%**                                                       |
| **61 to 80 Sites**                | **38%**                                                       |
| **81 to 100 Sites**               | **36%**                                                       |
| **101 or More Sites**             | **30%**                                                       |
+-----------------------------------+---------------------------------------------------------------+

[!IMPORTANT] Neutral-to-Ground Separation at RV Pedestals (NEC 551.72): The neutral (grounded) conductor and equipment grounding conductor must be kept strictly isolated at every individual RV park site pedestal disconnect. The neutral bus must NOT be bonded to the pedestal enclosure or grounding electrode; the system bonding jumper is located solely at the main service equipment.

4. Worked Plan Review Calculations & Common Traps

Worked Example 1: Marina Dock Feeder Calculation & GFPE Coordination

• Scenario: A new marina dock has 20 boat slips. Each slip is equipped with a power pedestal containing one 30A, 120V shore power receptacle (3,600 VA) and one 20A, 125V GFCI receptacle. The dock is supplied by a 120/240V, single-phase feeder from the main marina distribution panel.
• Step 1: Calculate Total Connected Shore Power Load
  • Under NEC 555.33, each 30A receptacle is computed at 3,600 VA (the 20A convenience outlet is not added to the 30A load for slip calculations). $\text{Connected Load} = 20 \times 3,600\text{ VA} = \mathbf{72,000\text{ VA}}$
• Step 2: Determine Demand Factor from Table 555.33(A)
  • For 15 to 30 shore power receptacles, the demand factor is 70% (0.70).
• Step 3: Calculate Demand Load and Feeder Ampacity $\text{Demand Load} = 72,000\text{ VA} \times 0.70 = \mathbf{50,400\text{ VA}}$ $\text{Feeder Current } (I) = \frac{50,400\text{ VA}}{240\text{ V}} = \mathbf{210\text{ Amperes}}$
• Step 4: Verify Overcurrent Protection & GFPE (NEC 555.35)
  • Select a standard 225A 2-pole circuit breaker (NEC Table 240.6(A)) protecting 4/0 AWG THHN Copper conductors (230A at 75°C).
  • The main feeder breaker must be equipped with <= 100 mA GFPE with time delay.
  • Each individual 30A slip receptacle breaker in the pedestal must have <= 30 mA GFPE.

Worked Example 2: RV Park Service Load Calculation

• Scenario: An RV park electrical service supplies 50 RV sites. The site layout consists of:
  • 15 sites with 50A, 30A, and 20A receptacles (9,600 VA each).
  • 35 sites with 30A and 20A receptacles (3,600 VA each).
• Step 1: Calculate Total Connected Volt-Amperes $\text{50A Sites Load} = 15 \times 9,600\text{ VA} = 144,000\text{ VA}$ $\text{30A Sites Load} = 35 \times 3,600\text{ VA} = 126,000\text{ VA}$ $\text{Total Connected Load} = 144,000\text{ VA} + 126,000\text{ VA} = \mathbf{270,000\text{ VA}}$
• Step 2: Apply Demand Factor from Table 551.73(A)
  • For 41 to 60 sites, the demand factor is 40% (0.40). $\text{Calculated Service Demand Load} = 270,000\text{ VA} \times 0.40 = \mathbf{108,000\text{ VA}}$
• Step 3: Calculate 120/240V Single-Phase Main Service Current $\text{Service Current } (I) = \frac{108,000\text{ VA}}{240\text{ V}} = \mathbf{450\text{ Amperes}}$
  • A standard 500A or 600A single-phase 120/240V service is required.

5. Plans Examiner Verification Checklist: Assembly, Marinas & RV Parks

• Places of Assembly Occupant Load (>= 100): Confirm building code occupant load calculation; verify all wiring methods are metallic raceways or Type MC cable.
• 1-Hour Fire-Resistance Exception: If Type NM or PVC is shown in an assembly occupancy, verify architectural drawings certify a minimum 1-hour fire-rated finish.
• Marina Shore Power GFPE (<= 30 mA): Verify all slip shore power receptacles are scheduled with <= 30 mA ground-fault equipment protection.
• Marina Feeder GFPE (<= 100 mA): Confirm all marina dock feeders are specified with <= 100 mA GFPE coordinated with downstream 30 mA devices.
• Marina Feeder Demand Factors (Table 555.33(A)): Check that load calculations apply proper demand percentages based on total slip count.
• Equipotential Bonding of Docks: Confirm plan details bond all metallic floats, pilings, and pedestals with minimum 12 AWG insulated copper conductors.
• RV Site Receptacle Percentages: Audit site distribution: verify 100% have 20A GFCI, >= 70% have 30A (TT-30R), and >= 20% have 50A (14-50R).
• RV Park Demand Factors (Table 551.73(A)): Verify service calculation uses 9,600 VA (50A) and 3,600 VA (30A) loads modified by Table 551.73(A) factors.
• RV Pedestal Neutral Isolation: Confirm no neutral-to-ground bonding jumpers exist at individual site pedestals.