recreational vehicle demand help

[IG88]

hey everyone, im writing a code essay and have been coming up short for hours. any help would be awesome.
This is CEC and the question is as fallows:

a recreational behicle park has the fallowing arrangement of receptacles:
15 of 50A, 120/240v 1-phase, 3wire
15 of 30A, 120v, 2 wire
and 30 of 15A, 120v, 2 wire

The service is 120v/208v, 3 phase, 4 wire. Equipment is rated at 100% continoius.
The aluminium conductors for the main service are required to be:
A) 461.32A, using 700kcmil R90 Al
B) 775A, using 3x350kcmil R90 Al in parallel
C) 461.32, using 2x300kcmil R90 al in parallel
D) 461.32, using 2x250Kcmil RW75 Al in parallel

 

[Npstewart]

Have you read article 551.73? Its pretty self-explanatory. I don't have my NEC at home with me but if you do, the section is really self explanatory. There is a chart in there to use, If you have a 50A receptacle you use about 9000VA/ pedestal, if its a 30A then you use a VA somewhere around 3000VA.

First thing you should do is count the total number of pedestals and find your diversity factor out of article 551.

Next I would assign each pedestal a VA amount based on the arrangment of receptacles.

Add it all together and multiply by 1.25 for continuous loading.

Next, find your wire size under the 75 degree column.

PS.

Just found a good article on ecmweb:

http://ecmweb.com/nec/code_calc_092304/

 

[Npstewart]

Oh, and after you find the total VA for all the pedestals, apply the diversity factor.

 

[Npstewart]

If you go to the website I have in my first post, they also have a example very close the question you asked.

 

[BAHTAH]

RV Park Service

RV Park Service

hey everyone, im writing a code essay and have been coming up short for hours. any help would be awesome.
This is CEC and the question is as fallows:

a recreational vehicle park has the fallowing arrangement of receptacles:
15 of 50A, 120/240v 1-phase, 3wire
15 of 30A, 120v, 2 wire
and 30 of 15A, 120v, 2 wire

The service is 120v/208v, 3 phase, 4 wire. Equipment is rated at 100% continuous.
The aluminium conductors for the main service are required to be:
A) 461.32A, using 700kcmil R90 Al
B) 775A, using 3x350kcmil R90 Al in parallel
C) 461.32, using 2x300kcmil R90 al in parallel
D) 461.32, using 2x250Kcmil RW75 Al in parallel

To begin with the NEC requires the minimum site receptacle to be 20 amps @120v so the thirty 15 amp does not meet code. I don't have my code book but I think the spaces are calculated at 9600VA for the 50 amp and those have to be 120/240 1ph34 originating from that system which means if your park has a 208y/120 3ph4w service you will need to figure some unit subs to create the 120/240 1ph3w for the 50 amp spaces. The 30amp I think are figured at 3600VA and the 20amp at 2400VA. Then you can check out the demand for your sixty spaces which will probably be in the 45% or so area. After all of that the code will have a note that basically says if you use the demand allowed, the system may not work. If you follow the sequence in the NEC it is fairly easy to follow.