Recreational vehicle parks.

[arnettda]

Trying to do voltage drop on a feeder feeding 10 50amp rv plugs. Length 900ft. Do I use 200 amps as my current? And do one voltage drop? Do I break it down in two different formulas say half way and then the end? Any help would be great.
Using 9600 watts per outlet.
Does 551.73D informal note mean I do 10 voltage drop calcs one for each length. But then what. Add them together? Or just look at them individually?
Thanks

 

[augie47]

I may be wrong, but as I see it, you can use the loads as shown in 551.73(A) and calculate the drop to the 1st spot, then use that newly calculated voltage and figure the drop to the second, and continue.
Keep in mind voltage drop is obviously important, but other than Art 647, I don't know of any Code requirement.

 

[charlie b]

It took me a couple minutes to duplicate your calculation to get 200 amps. Yes, you can use that value, and do one calculation. If you do, you might wind up using bigger wire than you might otherwise be able to use. The advantage of doing the calculation in steps is that you have a chance to reduce your wire sizes. You might even be able to start with a bigger wire for the first couple of runs, and a smaller wire for the next couple runs, and a smaller still wire for the remainder of the runs. It's up to you do decide whether it is worth the effort.

The voltage drop does add up along the path. If you drop 2 volts from the service to RV #1, and 1.5 volts from RV #1 to RV #2, then the total VD up to that point is 3.5 volts.

Here is how you set up the step-by-step VD calculation:

• From service point to RV #1, use a total load of 200 amps (based on 9600 x 10 x 50% / 240), and use the length of that portion of the run.
• From RV #1 to RV #2, use a total load of 198 amps (based on 9600 x 9 x 55% / 240), and use the distance between the two RVs.
• From RV #2 to RV #3, use a total load of 176 amps (based on 9600 x 8 x 55% / 240), and use the distance between the two RVs.
• . . . . . . (moving on) . . . .
• From RV # 6 to RV # 7, use a total load of 120 amps (based on 9600 x 4 x 75% / 240), and use the distance between the two RVs.
• From RV # 7 to RV # 8, use a total load of 96 amps (based on 9600 x 3 x 80% / 240), and use the distance between the two RVs.
• . . . . (you can figure out the rest). . . .

 

[zbang]

Are the connections/pedestals spaced along the feeder and tapped off or are they all at one end? I think the FPN is pretty clear:

Total circuit voltage drop is a sum of the voltage
drops of each serial circuit segment, where the load for
each segment is calculated using the load that segment sees
and the demand factors of 551.73(A).

You should have one calc per segment, so OCPD to first tap, tap 1 to tap 2, etc, then look at them both individually and in total. A spreadsheet comes in handy here.

edit: Charlie beat me to it.

 

[jumper]

Keep in mind voltage drop is obviously important, but other than Art 647, I don't know of any Code requirement.

Fire pumps. 695.7

 

[arnettda]

It took me a couple minutes to duplicate your calculation to get 200 amps. Yes, you can use that value, and do one calculation. If you do, you might wind up using bigger wire than you might otherwise be able to use. The advantage of doing the calculation in steps is that you have a chance to reduce your wire sizes. You might even be able to start with a bigger wire for the first couple of runs, and a smaller wire for the next couple runs, and a smaller still wire for the remainder of the runs. It's up to you do decide whether it is worth the effort.

The voltage drop does add up along the path. If you drop 2 volts from the service to RV #1, and 1.5 volts from RV #1 to RV #2, then the total VD up to that point is 3.5 volts.

Here is how you set up the step-by-step VD calculation:

• From service point to RV #1, use a total load of 200 amps (based on 9600 x 10 x 50% / 240), and use the length of that portion of the run.
• From RV #1 to RV #2, use a total load of 198 amps (based on 9600 x 9 x 55% / 240), and use the distance between the two RVs.
• From RV #2 to RV #3, use a total load of 176 amps (based on 9600 x 8 x 55% / 240), and use the distance between the two RVs.
• . . . . . . (moving on) . . . .
• From RV # 6 to RV # 7, use a total load of 120 amps (based on 9600 x 4 x 75% / 240), and use the distance between the two RVs.
• From RV # 7 to RV # 8, use a total load of 96 amps (based on 9600 x 3 x 80% / 240), and use the distance between the two RVs.
• . . . . (you can figure out the rest). . . .

Should I start with 240 volts and then use my new voltage every time I recalculate?