permitted to include additional receptacle configurations conforming to 551.81. The remainder

of all recreational vehicle sites with electrical supply shall be equipped with one or more of the receptacle configurations conforming to 551.81. Dedicated tent sites with a 15- or 20-ampere electrical supply shall be permitted to be excluded when determining the percentage of recreational vehicle sites with 30-or 50- ampere receptacles.
Additional receptacles shall be permitted for the connection of electrical equipment outside the recreational vehicle within the recreational vehicle park.
All 125-volt, single-phase, 15- and 20-ampere receptacles shall have listed ground-fault circuit- interrupter protection for personnel.
FPN: The percentage of 50 ampere sites required by 551.71 may be inadequate for seasonal recreational vehicle sites serving a higher percentage of recreational vehicles with 50 ampere electrical systems. In that type of recreational vehicle park, the percentage of 50 ampere sites could approach
100 percent.

551.72 Distribution System. Receptacles rated at 50 amperes shall be supplied from a branch circuit of the voltage class and rating of the receptacle. Other recreational vehicle sites with 125-volt, 20- and 30- ampere receptacles shall be permitted to be derived from any grounded distribution system that supplies

120-volt single-phase power. The neutral conductors
shall not be reduced in size below the size of the
ungrounded conductors for the site distribution. The
neutral conductors shall be permitted to be reduced
in size below the minimum required size of the
ungrounded conductors for 240-volt, line-to-line,
permanently connected loads only.

551.73 Calculated Load.

(A) Basis of Calculations. Electrical services and feeders shall be calculated on the basis of not less than 9600 volt-amperes per site equipped with 50- ampere, 208Y/120 or 120/240-volt supply facilities;

3600 volt-amperes per site equipped with both 20-
ampere and 30-ampere supply facilities; 2400 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 set
forth in Table 551.73 shall be the minimum allowable
demand factors that shall be permitted in calculating
load for service and feeders. Where the electrical
supply for a recreational vehicle site has more than
one receptacle, the calculated load shall be calculated
only for the highest rated receptacle.
Where the electrical supply is in a location that serves two recreational vehicles, the equipment for both sites shall comply with 551.77 and the calculated load shall only be computed for the two receptacles with the highest rating.
(B) Transformers and Secondary Distribution Panel- boards. For the purpose of this Code, where the park service exceeds 240 volts, transformers and secondary distribution panelboards shall be treated as services.

(C) Demand Factors. The demand factor for a given number of sites shall apply to all sites indicated. For example, 20 sites calculated at 45 percent of 3600 volt-amperes re-

Table 551.73 Demand Factors for Site Feeders and Service-Entrance Conductors for Park Sites

Number of Recreational Demand Factor

Vehicle Sites (%)

1 100

2 90

3 80

4 75

5 65

6 60 7-9

55
10-12 50
13-15 48
16-18 47
19-21 45
22-24