Code Calculations

Sep 23, 2004 11:21 AM, By Mike Holt

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