Code Calculations

Sept. 23, 2004
According to the U.S. Census Bureau, there are more than 3,500 recreational and vacation camps in this country. That's a lot of supply facility sites for recreational vehicles. Although the work may not be performed on a regular basis, do you know the ...

According to the U.S. Census Bureau, there are more than 3,500 recreational and vacation camps in this country. That's a lot of supply facility sites for recreational vehicles. Although the work may not be performed on a regular basis, do you know the rules for sizing services for these facilities? If not, read on and then test your skills by tackling our sample question.

Recreational vehicle parks are calculated according to the demand factor of Table 551.73. The total calculated load is based on:
• 2,400VA for each 20A supply facilities site
• 3,600VA for each 20A and 30A supply facilities site
• 9,600VA for each 50A, 120/240V supply facilities site

Ready for a quiz? A recreational vehicle park has 42 sites: three are rated 50A, 240/120V; 30 are rated 30/20A; and nine are rated 20A. What's the minimum feeder demand load for these sites?

A) 158kVA
B) 101kVA
C) 139kVA
D) 65kVA

Answer: As per the requirements of 551.71, 551.73(A), and Table 551.73, the correct answer is 65kVA. Note: A minimum of 70% of the sites must have a 30/20A facility (3,600VA per site). Find the answer as follows:

Step 1: Determine the total connected load.
3 sites at 50A = 3 x 9,600VA = 28,800VA
30 sites at 30A = 30 sites x 3,600VA = 108,000VA
9 sites at 20A = 9 x 2,400VA = 21,600VA
Total load = 28,800VA + 108,000VA + 21,600VA = 158,400VA

Step 2: Determine the demand factor per Table 551.73.
In this case, it's 41%.

Step 3: Determine the net computed demand load:
158,400VA x 0.41 = 64,944VA ÷ 1,000 = 65kVA

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

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