RV Park feeder calculation

[sw_ross]

This is just for practice. Attached is a scenario to calculate a feeder from an MDP to a row of ten RV pedestals. I would appreciate some feedback on whether this is "real-world" or not.

I haven't accounted for voltage drop, I'm not sure how to account for varying loads located incremental distances from the source. A hint or a clue to steer me in the right direction would be appreciated.

Also, would the pedestals be considered "structures" in regards to ground? I know I would have to run a 4-wire feeder to the pedestals, I'm just wondering about whether each pedestal would have to have a grounding electrode to comply with 250.50?

Thanks for any feedback,
Sky

 

[charlie b]

You have a good start, and if you wished you could end it there. But you don?t have to use the 250 MCM wire all the way to the end. You can do a step by step load calculation and voltage drop calculation. Spreadsheets are good tools for this process. Essentially, it goes like this:

• Step 1: from MDP to pedestal 1. 200 amp load, distance 50 feet. Select the 250 MCM AL wire (as you have already done). Calculate VD along this part of the run. My result is 1.03 volts. Do not go by percent VD, but rather by actual volts.
• Step 2: from pedestal 1 to pedestal 2. 9600 VA times 9 pedestals times demand factor of 55% is 47,520 VA, equivalent to 198 amps. You now have a 198 amp load, distance 30 feet. Stay with the 250 MCM AL wire. Calculate VD along this part of the run. My result is 0.61 volts. Total VD so far: 1.03 plus 0.61 equals 1.64 volts.
• Step 3: from pedestal 2 to pedestal 3. 9600 VA times 8 pedestals times demand factor of 55% is 42,240 VA, equivalent to 176 amps. You now have a 176 amp load, distance 30 feet. Now you can drop to 4/0 AL wire. Calculate VD along this part of the run. My result is 0.64 volts. Total VD so far: 1.64 plus 0.64 equals 2.28 volts.

You are on your own for the rest of the calculation.

 

[Npstewart]

Probably wouldn't be a bad idea to add a distribution panel between #5 & #6 to feed the others and cut down on the VD