Supply Voltage

[Kirk]

The 2 50A legs in the 120VAC main panel configuration requires the neutral to carry some current.

The neutral is called that because it is the center-tap of a 240 VAC home transformer. It does nothing at all on a 240 VAC circuit.

Post #13 is exactly what I would expect in a 50A supply RV

When using any properly wired, 4 pin, 50A RV outlet, the neutral will carry the difference in current between the two legs of opposite polarity. If L1 is drawing 15A and at the same time L2 is using only 10A, the difference of 5A will be returned via the neutral lead.

 

[DonTom]

119 volts is now delivered to each A/C and no current on the neutral Zero. Zip. Nada, Perfectly balanced..

If perfectly balanced with no neutral, you have 240 VAC supplying two 120 VAC A/Cs in series. That will give each 120 VAC. Connect up the neutral (as in normal) then the neutral has the full current from both A/Cs one at a time, along with the other stuff running on each leg, which is usually far from zero current.

-Don- Reno, NV

 

[OldWEB]

If perfectly balanced with no neutral, you have 240 VAC supplying two 120 VAC A/Cs in series. That will give each 120 VAC. Connect up the neutral (as in normal) then the neutral has the full current from both A/Cs one at a time, along with the other stuff running on each leg, which is usually far from zero current.

-Don- Reno, NV

I really thought you understood it back in post #5...
With only the two A/Cs on, there will be NO current on a connected neutral.

 

[OldWEB]

I said the neutral carries NONE or Nearly NONE So yes I was talkign EXACTLY
Here is how it works and why. I'd hoped to avoid this post.

Let's say the only thing in the RV is a pair of Air Conditioners. Everythign else is off. Both Ac's are drawing 13 amp precisely.. One on each leg.. Let's say that due to the length of the run from the transformer to the RV the total voltage drop is 1 volt.. 240 volts 120 volts either side of neutral comes out the transformer. 119 volts is now delivered to each A/C and no current on the neutral Zero. Zip. Nada, Perfectly balanced.. NOTE this is nearly NEVER the case.. WHY Well the Converter is drawing a but of power and it's on one leg.. So that current WILL be carried on the neutral.

Let's shut off one of the Air Conditioners.. Now we have one volt drop TO the RV and one Back from the RV to the transformer via the neutral line since it is not carrying 13 amps... the voltage to that single AC is not 19.. but 118 This is why your house, be it mobile or fixed. is wired for 240 volts divided by a neutral 120 either side of neutral.

Of course in real life the neutral Will carry current. but only the difference between L1 and L2 and occasionally that gets to be real real low.

Had a high resistance Neutral at home once.. Was amazing to watch a pair of voltmeters when a big 120 volt device kicked in... Cost me a few light bulbs before I called the power company and they fixed it.

Now this explanation takes the proverbial cake...
What does the voltage drop have to do with 120/240V neutral currents?
And with half the current you will get twice the voltage drop? Where? At all times there are only two wires involved in supplying current...
Also if two A/Cs are running you will have BOTH currents running thru the two hot legs for a total of 26 amps... that is when/where you would have more of a voltage drop.
Did "Happy hour" start early?

 

[DonTom]

With only the two A/Cs on, there will be NO current on a connected neutral.

Like I said, that would be the same as both A/Cs in series running from 240 VAC. No need for the neutral when the balance is perfect. Disconnect it and then ONLY no difference.

But we do not live in such a perfect world.

So that is not reality in an RV. For an example, you have a converter running only on one side of the AC line along with many other items on either side of the 120 VAC. Perfect balance is unlikely in reality. Then the difference is in the neutral.

-Don- Reno, NV

 

[Gary RV_Wizard]

The vast majority of RV's built in the last 25 years are called "50A service".

Don't know about a "vast majority" but it's greater than it was a decade or so ago. However, a high percentage of RV sales are still smaller trailers and class B or C coaches where 30A/120v is still the most prevalent configuration.

I think the key point is that 50A/240v is NOT universal, either in new RV production or RV park design. It's a design choice that is determined by the target price range and usage.

 

[OldWEB]

Thanks Gary, I will leave it at that, at least until another simple question, that turns into a technical question comes up! Most likely the same topic... or TP preference... or tank cleaning procedure....

 

[Ray-IN]

You made the same mistake again. That would be 24,000 watts. A 14-50R is only good for 50-amps/240 VAC. The amp rating is what the "50" means in 14-50R or 14-50P.

It's a total of 50-amps at 240 VAC (240V times 50 amps=12,000 watts).

It's a total of 100 amps at 120 VAC. 120 VAC times 50 amps=6,000 watts. Twice (two lines, each hot in respect to neutral) for the same 12,000 watts. But that is still only 50-amps on each 120 VAC connection.

You're not going to lose or gain any power (watts) capacity either way. But if your total voltages will be half, it means you can double the TOTAL current draw to get the exact same wattage capacity at half the voltage.

So the one thing that stays the same in all of this is the 50-amps. 50 amps times one at two 240 VAC. Or 50-amps times two lines at 120 VAC. Total wattage capacity is also the same in each.

All three have a 50-amp limit, but at 120 VAC you have that 50-amp limit twice, 50-amp capacity on each line.

-Don- Reno, NV

I see a light at the end of the tunnel. 50 X 120=6,000 X 2 =12,000; 50 X 240 = 12,000. (hope it isn't an oncoming train)
I can testify the brain of an 81 yr old man does not function like the brain of a 60 yr old man. Which is why I'm not going to vote for either of them.
Sorry brain-drift.

 

[dktool]

Don't know about a "vast majority" but it's greater than it was a decade or so ago. However, a high percentage of RV sales are still smaller trailers and class B or C coaches where 30A/120v is still the most prevalent configuration.

I think the key point is that 50A/240v is NOT universal, either in new RV production or RV park design. It's a design choice that is determined by the target price range and usage.

I initially started this post when my daughter went shopping for a new, as in spankin new TT in the 26' range.
Well she landed on one and it is 240/50 with the split phase panel configuration that was layed in post #13.

Thanks for the info fellas !