Understanding 50A in my RV

[RobWNY]

I understand there are two legs, each carrying 50 Amps to the RV but I'm having trouble understanding what gets serviced by L1 and what gets serviced by L2 of the 50A service and why are there two legs on a 50A service? I can just turn off one of the main breakers and check each outlet and AC unit and figure out that part of things but I'm more interested in knowing why it's done that way. I have two air conditioners. A 15,000 BTU AC in the living area and a 13,500 BTU AC in the bedroom. If I'm on a 30A service, I know I can't use both of them at the same time because of the start up surge needing too many watts but I can use both theoretically on one leg of a 50A service. So why are there two legs and why is that necessary? Why not just one leg of 75A or 100A to handle the loads from AC units, the Microwave, Washer/Dryer etc.? There are many homes with 100A services still so why are RV's different?

[javankrona]

I would like to expand this topic a bit and look at the RV pedestal for 50amp service. The park I’m at has L1 and L2 at 120v, but only 208v across L1/L2. My Southwire ATS is looking for 240v across L1/L2. My clothes dryer and cheap heat also draw 240v. Regardless, my ATS  will only allow one leg of power to the rig from the pedestal; basically a 30amp power supply from a 50amp supply. Is the pedestal not wired properly at the park?

[road-runner]

Sounds like the pedestal is wired to 2 legs of a 3-phase feed, not horribly unusual in a large installation.  Last I heard it was pretty unusual for an RV to have any 240 volt devices.  You should be able to draw 50 amps on the one leg.

[joebedford]

Is it very hot and the park very crowded? If so, the combined load can drop the voltage to 208. 104V on each leg may damage some components in your RV.

[wa8yxm]

Most houses have 120/240 volt service. The 50 amp RV is identical to these.

Look at your breaker box.. Now depending on the box your main breakers will be either at the top. on the left or in the middle.

Generally if they are in the middle then breakers on one side are L-1 and the other L-2 (Which is which is kind of arbaratary)

if they are on the end then it's 1.2.1.2.1.2

If they are on top well

1 2
2 1
1 2
is common also
1 2
1 2
Depeding on the box if "Mains" flip up and down and the branch sideways
Then the top configuration is likely.
Push-matics (Never seen an rv with 'em) use the bottom.

[sayoung]

BB_TX wrote:
Not unusual on some newer RVs to have 120 vac distribution panels with the main 50 amp breaker in the center position with L1 sub breakers on one side and L2 sub breakers on the other side.

That's the way my panel is wired. You can only get 240 at the main breaker by using a dbl thin but I see no need of 240 for my stuff.

[DownTheAvenue]

rhagfo wrote:

DownTheAvenue wrote:

RobWNY wrote:
There are many homes with 100A services still so why are RV's different?

RV's aren't different. They are wired exactly the same. Some homes have 200 amp service and are wired exactly the same as a 50 amp RV.

Well not quite correct, in a house panel you can tap 240 volt circuit simply by installing a double breaker for your panel that will connect one breaker to each leg. In an RV the legs split at the main breaker, giving two legs of 120 50 amp capacity. You can get one 240 volt circuit by using a double breaker with half size breakers in place of the main. Typicality you would install a 50/30 double half size breaker the 50 being the main and the 30 being a 240 volt feed for a dryer, or in my case my Cheap Heat system.

You are quite wrong! See Doug's post below who knows what he is talking about!!!!

[Bobbo]

RobWNY wrote:
Thanks for the explanation. That makes sense now. So I assume where you say the "RV can pick whether it wants to use the power as two 120v circuits, or as a single 240v circuit" that is determined at the panel and how the RV has been wired at the factory?

Precisely.

[rhagfo]

dougrainer wrote:
Remember. On most RV 50 amp interior breaker boxes, The L1 and L2, it is every other breaker on the legs. L1, powers the 1/3/5/7/9 and L2 powers the 2/4/6/8/10. L1 and L2 makes no difference in this. L2 could be ODD and L1 could be EVEN. There are exceptions, but this is true for most. Doug

Not on RVs I have owned, and likely most 50 amp RVs. The buss is split at the main breaker located in the center of the breakers those to the left on one leg those on the right on the other leg. If it was as you describe, then picking up 240 volts at the panel would be easy. As it is only was is a double - double half space breaker for the main and the other double to feed a 240 volt appliance.

[theoldwizard1]

RobWNY wrote:
I can just turn off one of the main breakers and check each outlet and AC unit and figure out that part of things ...

Probably not. Usually the two handles are mechanically tied together.

[RobWNY]

Thank you valhalla360, you've explained things further and I appreciate it! Having the history behind the explanation is always a plus. At least to my brain 🙂

[valhalla360]

Bobbo wrote:

Why does the US/Canada do it differently than the rest of the world? Because, we can. It would have been just as easy to only use 240v here, then you wouldn't have, or need, two legs.

Mostly an historical issue. North America got the first grids and the local delivery portion tended to be a lot of focus on lights. That didn't take a ton of power and if you had low voltage, the lights still worked (just a little dimmer).

By the time they realized that they needed more power, it was going to be very expensive to upgrade everything to 240v. Instead, they did smaller incremental voltage increases. That's why you will hear people talking about 110v, 115v and 120v.

Since other parts of the world developed their grids later, they jumped straight to a higher voltage...but don't think it's all perfect and consistent, they still have issues going from country to country.

As far as the RV, it's pretty much identical to a typical household system except only 50amp @240v rather than 100-400amp @ 240v.

The fundamental issue driving the voltage is amperage per cable. The more amps, the bigger the cable required. By splitting out the loads, you can keep the cables manageable (though people already complain about 50amp cords). If you jump that up to 75-100amps, the cables become drastically larger.
- 30amp cords are typically 10 gauge (2.59mm diameter -5.26mm2 area)
- 50amp cords are typically 6 guage (4.11mm diamter - 13.29mm2 area)
- theoretically to run 100amp, you would want to jump up to something like a 3 gauge (5.83mm diamter - 26.65mm2 area)

As you can see the cables get really thick as the amperage goes up and it's not just your extension cord but the cables throughout the park.

50amp campsites only became common in the last 20-30yrs, so the issue of higher demand was already known. If you are putting in 50amp-120v, it costs next to nothing to jump up to 50amp-240v (mostly just a small increase in cost for the extra copper in the cabling), so it made a lot of sense to jump straight to the higher voltage system.

And if you look, the newest biggest rigs often have 3 air/con units, electric stoves, and a host of other electrical devices. 3 air/con units can draw 40amp @ 120v continous, so it would be marginal to handle the startup load on the 3rd air/con with the other 2 already running...let alone anything else. By splitting out the loads across both legs, it works a lot better.

[RobWNY]

I'm understanding this much better now. Thank you to all!

[BB_TX]

Not unusual on some newer RVs to have 120 vac distribution panels with the main 50 amp breaker in the center position with L1 sub breakers on one side and L2 sub breakers on the other side.

[dougrainer]

Remember. On most RV 50 amp interior breaker boxes, The L1 and L2, it is every other breaker on the legs. L1, powers the 1/3/5/7/9 and L2 powers the 2/4/6/8/10. L1 and L2 makes no difference in this. L2 could be ODD and L1 could be EVEN. There are exceptions, but this is true for most. Doug