SCHOOL ME ON RV OUTLET VOLTAGE DROP CALCULATIONS

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Houston714

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Hi all! I've got a 285 ft. run for a 50 amp RV outlet. The situation is different due to voltage 120/208 single phase.
1. Are not most all RVs 120 Volt loads?
2. Should my Calculations be based on 120 not 208 sing phase?

My Calculations came out to a 1/0 Aluminum Stranded 4 conductor at 3%.

If I did a 30 amp 120 RV outlet it still calls for a 1/0 Aluminum Stranded 3 conductor at 3%.

Thanks for the help! Screenshot (2).png
 

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1. Nope. A 50a RV supply is 120/240v. As with any service, it will work fine, except 240v loads must be compatible with 208v, and 240v heating appliances will operate at 75% power.

2. I'm thinking you should use 120v loads for L-N loads on each line, and 208v for L-L loads.
 
I understand. I was informed that all loads on this RV are 120... so I should I do the load Cal? At 30 amp 120?? I'm kind of confused at this point my friend... the cord on the RV is a 50 amp 4 prong... and a adapter 30 amp 3 prong.... and an adapter 20 amp 3 prong....
 
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Got you! I haven't seen the RV...
the cord on the RV is a 50 amp 4 prong... and a adapter 30 amp 3 prong.... and an adapter 20 amp 3 prong....
So I need to ask what the highest current device is on the RV... Doubt they will know... this is becoming a nightmare LOL!
 
The highest draw would be if you use the adapter(s), because they join both lines into one.

The adapters are only for 120v, so you would simply add the two 120v line currents.
 
So I just spoke with owner. He said it has 2 AC's, a grinder, and a ventilation duct for the grinder. Its been converted to a PGA Club repair RV. He told me that they have plugged it in the 20 amp adapter and cut everything on and it blew the breaker pretty quick, but seemed to get by with the 30 amp adapter. I'm guessing with both AC's are the big draw...
 
Since voltage drop is the concern, and it should be, you should definitely wire for the higher voltage.

One more conductor literally halves your load (or as close as you can get with load balancing.)

For example, the two ACs should be on opposing lines, as should the grinder and the ventilator.
 
Your right... opposing sides! Cant' say PH word!
Yep! The calculations listed above were what I came up with, unless you saw something I missed. If I can can get a 2/0 aluminum direct burial 4 conductor, I will, It won't hurt.

I'm surprised no one else chimed in on this on...
 
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Houston714 said:
Your right... opposing sides! Cant' say PH word!
Click to expand...
I almost posted that "phases" would actually be correct here. :giggle:

I'm surprised no one else chimed in on this on...
Click to expand...
Maybe I got it right. o_O I'll let you determine the load and the VD.

Actually, you should use one AC and the grinder or ventilator current (whichever is greater) as your load.
 
50 amp RV plug is 120/240 at the receptacle.

But, few, if any, RV’s use 240.

The plug just splits it into 2 120 volt loads.

Thats why a 20 or 30 amp adapter works. It’s still 120 volts to the entire load center in the RV, just less power.
 
I= 50
R= 0.057 ohms (Chapter 9, Table 9 for a 1/0 Aluminum wire: (.20/1,000 feet) x 285 feet
Voltage Drop = 50 amperes x 0.057 ohms

Voltage Drop = 2.85 volts, (2.85 volts/208 volts = 1.37% volts drop)
2.85 volts, (2.85 volts/120 volts = 2.87% volts drop)

DOES THIS LOOK RIGHT??????????????
 
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Be patient. The engineers among us will respond soon. You probably know more about VD calculations than I do.
 
Houston714 said:
I understand. I was informed that all loads on this RV are 120... so I should I do the load Cal? At 30 amp 120?? I'm kind of confused at this point my friend... the cord on the RV is a 50 amp 4 prong... and a adapter 30 amp 3 prong.... and an adapter 20 amp 3 prong....
Click to expand...
If 30amperes is your largest load than it looks to me with 1/0 would work?

2 x 21.2 x 285 x 30= 362,520/3.6volts=100,700

1/0 is next size up at 105,600cmils.

Also have to make sure you proportionally increase your EGC.
 
Thanks! So what about for a 50 amp? 2 Hots, a neutral and EGC... not quite getting your formula unless your using 3% on 120 to 3.6 volts.
I'm trying to get what really needs out there besides a 30 amp 120 v if I can.... 2- 120 v legs, a N and EGC.

I thought the 1/0 would have covered it for 50 4 prong too:

I= 50
R= 0.057 ohms (Chapter 9, Table 9 for a 1/0 Aluminum wire: (.20/1,000 feet) x 285 feet
Voltage Drop = 50 amperes x 0.057 ohms

Voltage Drop = 2.85 volts, (2.85 volts/208 volts = 1.37% volts drop)
2.85 volts, (2.85 volts/120 volts = 2.87% volts drop)

WHAT IS YOUR CALCULATION FOR A 50AMP 2P PAL?
 
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At this point I have to presume its a balanced panel.
According to your Calculations, If I do it for 50:
2x21.2x50x285= 604,200/7.2=83,916.
Next size up 105,600 which is a 1/0... should cover it also for 50amp 2H,1N,1EGC

I'm gonna check to see if they have a 2/0 direct burial 2H 1N 1EGC
 
Houston714 said:
Thanks! So what about for a 50 amp? 2 Hots, a neutral and EGC... not quite getting your formula unless your using 3% on 120 to 3.6 volts.
I'm trying to get what really needs out there besides a 30 amp 120 v if I can.... 2- 120 v legs, a N and EGC.

I thought the 1/0 would have covered it for 50 4 prong too:

I= 50
R= 0.057 ohms (Chapter 9, Table 9 for a 1/0 Aluminum wire: (.20/1,000 feet) x 285 feet
Voltage Drop = 50 amperes x 0.057 ohms

Voltage Drop = 2.85 volts, (2.85 volts/208 volts = 1.37% volts drop)
2.85 volts, (2.85 volts/120 volts = 2.87% volts drop)

WHAT IS YOUR CALCULATION FOR A 50AMP 2P PAL?
Click to expand...

2 x 21.2 x 285 x 50=604,200/6.24vd= 96,826cm ( 1/0 as well )
 
You do understand that voltage drop is dependent on load current and not breaker size, right?

Sure, you can use 50 amps if you wish, for the worst-case scenario.
 
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