Calculating voltage drop

[tessab]

In determining which size wire to use, what load do we enter when calculating voltage drop when adding a 50 amp RV site when the electric service is a 240 volt, 50 amp breaker and RVs technically run on 120 volts? Do we count the RV as 50 amps, or can we count it as just 25 amps since the RV essentially has two 120 volt, 25 amp circuits?

[StirCrazy]

tessab wrote:
In determining which size wire to use, what load do we enter when calculating voltage drop when adding a 50 amp RV site when the electric service is a 240 volt, 50 amp breaker and RVs technically run on 120 volts? Do we count the RV as 50 amps, or can we count it as just 25 amps since the RV essentially has two 120 volt, 25 amp circuits?

here is a link to a voltage drop calculator you'll never get ) voltage drop but you can keep it pretty low, I shoot for under 1.5%.

Steve

[Grit_dog]

enblethen wrote:
OP was asking for voltage drop trying what I believe is wire size for a Fifty amp receptacle.
No real need to use anything larger than the normal # 6 wire. It would be good for at least 50 feet then connecting to the 25–30-foot cord from the rig.

Thank you for being the first to post an accurate, on topic and concise answer!
I didn’t because the Op never even alluded to the length of run, but yes 6ga copper is sufficient to at least 250ft run.

[tessab]

Thanks everyone for your input!

[enblethen]

OP was asking for voltage drop trying what I believe is wire size for a Fifty amp receptacle.
No real need to use anything larger than the normal # 6 wire. It would be good for at least 50 feet then connecting to the 25–30-foot cord from the rig.

[wa8yxm]

BB_TX wrote:

Not exactly true. It is theoretically possible to pull 50 amps thru leg 1 while simultaneously pulling anything from zero amps to 50 amps on leg 2. Or vice versa. The neutral current would vary accordingly. In which case one leg would have more voltage drop than the other. And if one leg were pulling zero current, all voltage drop would be on the leg actually pulling current. A completely unbalanced load is as unlikely as a perfectly balanced load. Still, the voltage drop will not likely be equally shared.

You are correct but it's darn hard to do.. it's also theoretically possible to draw the full 50 amps on both legs but as I said it will never happen.

Figure the voltage drop as though you are going to be drawing 50 amps at 240 volts and you will be good for most RV's

[2oldman]

BB_TX wrote:

2oldman wrote:
OP's gone.

Happens often.

So often that I try to always ask a question first. It saves a lot of typing.

[BB_TX]

2oldman wrote:
OP's gone.

Happens often.

[Grit_dog]

2oldman wrote:
OP's gone.

You’re probably impatient.
Weather is beautiful in NM right now. Maybe time to get outside.

But yes, as usual, the usual constituents have muddled the discussion, lending little real world help to someone who was/is obviously not very well read on the subject.

[2oldman]

OP's gone.

[stevenal]

time2roll wrote:
The split phase has the advantage of sharing the neutral and reducing voltage drop.

Of course we all carefully balance our loading across the two legs to ensure minimal voltage drop. If I were doing this installation, I would assume the end user would not be that careful. Worst case is 50 A on one leg and neutral, zero on the other leg. 120 V in the formula at twice the distance.

[BB_TX]

wa8yxm wrote:
………

Example.. Let's say the run is long enough you calculate 1 volt drop each way.
So your total drop at max load is 2 volts.

But the max drop on EACH leg is 1 volt

NOTE: you will never hit max load.. It just does not happen as it would require PERFECT balance……….

Not exactly true. It is theoretically possible to pull 50 amps thru leg 1 while simultaneously pulling anything from zero amps to 50 amps on leg 2. Or vice versa. The neutral current would vary accordingly. In which case one leg would have more voltage drop than the other. And if one leg were pulling zero current, all voltage drop would be on the leg actually pulling current. A completely unbalanced load is as unlikely as a perfectly balanced load. Still, the voltage drop will not likely be equally shared.

[enblethen]

CA Traveler gave the correct definition of a 50 amp RV shore power connection.
It is a 120/240 volt four wire system.
Most standard RVs would normally not draw anywhere near 50 amps on each leg.

[wa8yxm]

If figuring voltage drop for a 50 amp RV
You figure 50 amps.. And don't forget the wire is twice as long as the run.

BUT also remember the drop is split between the two legs.
So you halve the drop for 120 volts.

Example.. Let's say the run is long enough you calculate 1 volt drop each way.
So your total drop at max load is 2 volts.

But the max drop on EACH leg is 1 volt

NOTE: you will never hit max load.. It just does not happen as it would require PERFECT balance.> But that's how you figure it. Just to be safe.

[KD4UPL]

50 amp, 240 volt. Don't make it complicated.