RV Voltage drop calc

[slice]

Hello All I was checking a voltage calc that was done for a RV park and I had a question. When they did the calc they used 240V as the voltage. I was thinking that theoretically if the RVs had only single phase loads doesn't it make more sense to use 120V instead of 240? Maybe this is unrealistic as the RV would never draw the full receptacle rating on a single hot leg but in theory it is possible. What do you guys think? Should the cables be sized for 120V or 240V? This is your standard 50A 4-wire receptacle.

Thanks

 

[luckylerado]

Depends. Was the value for "I" based on 240V loads or 120V? I assume that the VD calculation was for the feeder? I would think that in this case the VD would be figured for 120V on the heaviest phase knowing that most of the RV loads will be 120V.

 

[slice]

The calculation was actually for the branch circuits to each RV pedestal. They used 50A in the calculation as the current. I am not sure I agree with using 50A, I am leaning towards using 40A for each RV for the purposes of voltage drop.

 

[winnie]

If you are calculating out to a single pedestal, meaning a single RV user, then I would consider two scenarios: a higher amperage 240V load (larger RV using both legs of the 50A circuit) or a smaller amperage 120V load (smaller RV using a splitter and only using 1 leg of the 50A circuit). A large RV using the full 50A circuit should be balancing the internal 120V loads, and so really is a 240V load.

-Jon

 

[Smart $]

IMO, the likelihood of an RV to be electrically modified to the point of exceeding NEC limitations is much higher than a permanently-fixed home. Therefore, I would figure voltage drop at current not lower than receptacle rating.

Voltage drop of 120V vs. 240V is equal, with all other parameters being equal. What is different is the percentage of drop... 120V will be double that of 240V.

 

[slice]

IMO, the likelihood of an RV to be electrically modified to the point of exceeding NEC limitations is much higher than a permanently-fixed home. Therefore, I would figure voltage drop at current not lower than receptacle rating.

Voltage drop of 120V vs. 240V is equal, with all other parameters being equal. What is different is the percentage of drop... 120V will be double that of 240V.

Thanks for the replies. Yes I agree just the percent voltage drop will change and that is what had me concerned to begin with. I know you are not supposed to exceed 5% total between branch and feeder circuits. If you were maxing out the receptacle using only a single leg then the voltage drop percent would be twice the value of a 240V load. So does it make sense to size the branch circuit based on 120V percentage at 50A?

 

[winnie]

IMHO no.

As I understand things, the most common RV plugs are 120V 30A _or_ 120/240V 50A. IMHO it makes most sense to evaluate the 120V branch at 30A and the full 240V circuit at 50A, but 120V at 50A would be overkill.

-Jon