RV park calculations

[lbarnes]

I have been reviewing Article 551 in preparation for designing an RV park electrical renovation, where all the existing service pedestals are being upgraded to 50-ampere pedestals. I am trying to understand the permissible demand factor table (Table 551.73) in light of voltage drop calculations.

551.73(C) seems to give permission to apply the demand factor to the individual load as well as the total load. Since I intend to run individual dedicated feeders from the service panel to each pedestal, I am not sure I can apply the demand factor to the feeder. Also, the fine print note warns against using the demand factors in areas of extreme temperature. Since this is south Georgia, it might not be a good idea to apply any demand factor at all.

However, if no demand factor is applied, the voltage drop to the farthest pedestals dictates use of a wire size (1/0 AWG) which will not fit under the lugs of a 50-ampere breaker.

My only alternative appears to be to provide additional distribution panels so that the distance to the load is reduced.

I am hoping someone might have some thoughts on whether it is permissible to apply the demand factors to the dedicated feeders in this case.

 

[stew]

Re: RV park calculations

Im doing a project in a boatyard which is similar in nature. The code use a demand factor table that is similar to the one for rv parks except they use the number of receptacles instead of sites. The table in my case refers to service entrance conductors and feeders as well. Each of these must be calculated separatley. In other words the service conductors first and the feeders next. I had 75 outlets so it presented a problem as well splitting up this load on each individual panel. ie when the number of outlets drop so does the resultant demand factor. In my case I am using a premanufactured quad outlet pedastel that has 4 30 amp outlets with breakers in the box. It has large feed thru lugs and we can get 4 on each branch service panel using 4/0 wire direct burial. Lugs are good for 500 mcm. You might want to see if something simalar is available for rv sites that has a feed thru system so you can use a large feeder to feed several outlets.

[ June 17, 2004, 12:10 PM: Message edited by: stew ]

 

[bob]

Re: RV park calculations

I am asumming that this park is for overnite traverlers and not for permanent customers.
I do not think 551.73 is applied to an individual service to an individual trailer. 551.73 seems to require a load of 9600 watts per site with a 50 amp supply. I think the demand factor in 551.73C seems to be for a transformer or main switch which would supply a number of sites. I think you are goind to have to come with a diversity factor to apply to an individual trailer. The main load would be the lights, A/C unit, range, dryer and maybe a water heater. Problem is what load do you choose for the A/C unit when you know each trailer have different sizes.

 

[stew]

Re: RV park calculations

using the same requirements as for a boatyard each feeder is calculated separatly. if you have for instance 10 sites at 9600 va = 96000 total div by 240=400 x.50 demand = 200 amp feeder and 200 amp disconnect.Then you determine how you are going to feed the load. with individual branch circuits breakered at the main panel individually and then to tthe site where it also must have a disconnecting means either a breaker or a switch per 551.77(B).If you feed individually then of course you just use the 50 amp ampacity again accounting for voltage drops. By using the loop thru pedastels like we are using and feeding them in our case with 4/0 al the voltage drop is not a problem.Makes for a relatively simple installation as well.