Originally Posted by donniedu
Unless your living in it I just see no need to run a 50A circuit. 30 A will allow you to run one AC.
BTW search online for a correct 50A RV wiring diagram. It is a 30A and a 20A 120VAC system.
To understand the relationship between voltage and current is not "overly" complicated, so bear with me.
As many have stated previously, a 50 amp wired coach has what is called a "split phase" 50 amp 120 VAC service. The 220 VAC supply panel is "split" with 120 VAC L1 on one side and 120 VAC on L2 on the other, with a "Neutral" that is common to both circuits.
Alternating Current (AC) means that the direction of the current alternates between the "hots" (L1 or L2) every 1/60th of a second (called 60 cycle AC).
Voltage measured between L1 and L2 would be 220 volts AC with the direction of flow alternating between the two.
When a Neutral is used, the source phased voltage is "split" in the middle with 120 volts AC available on each (L1 and L2 when measured relative to the Neutral).
Then, every 1/60th of a second, when voltage between on L1 is "positive", the Neutral becomes the return path for that leg of the circuit. Concurrently, it ALSO becomes the "positive" for the L2 120 volt current flowing through to the L2 side ("negative" if you will). Then 1/60th of a second later everything alternates the other direction from L2 through the Neutral to L1.
Because of this relationship, the identical current is available on both sides of your 120 volt AC panel ALL THE TIME.
How MUCH of the current YOU have available to use is "limited" by the protection that is installed at the source to protect the wiring and equipment being used down stream. That protection, (the circuit breaker), is "Ganged" so that an overload on one leg will trip both legs OFF to protect the Neutral source wire.
Remember that BOTH sides "see" the same available current. If the campground's 50 amp service is wired correctly, each leg will always have 50 amps of service available to be used because it is limited by the campground's pedestal breakers and not for any other reason.
Because of the purpose of your camper's circuit breakers is to prevent circuit current from exceeding the rating of your camper's wires (including your connecting wire from the camper to the pedestal) and your installed equipment (like outlets and direct wired appliances) and not the campgrounds (which is protected by the pedestal breakers).
Remember also that the breaker is there to keep you from exceeding the maximum current that is safe for your wires on each leg. The actual current you are using on each leg is the sum of everything you have turned "on".
You can have 28 amps of stuff on one leg and still have 45 amps of stuff on the other because you can be using a total of 100 amps (just never more than 50 on a side).
Most campground's also have other service connections (sockets) on their service panel (typically a 30 amp and a 20 amp duplex each on their own breaker).
Those sockets can be wired "upstream" of the 50 amp service breaker or "downstream" of the 50 amp breaker depending SOLEY on the campgrounds pedestal service wires!
In order to be wired "upstream", the campground's service wires to the pedestal must be capable of "serving" 100 amps of service to the pedestal. In this case, all the sockets are capable of providing their full rated power without tripping any others.
However, many older campgrounds are wired for only the service rated on that campground's loop. So for the 50 amp loop, the supply wires are sized/rated only to provide 50 amps to each campsite.
In this case, the additional sockets are wired "downstream" of the 50 amp "main" protection breaker. Normally, the 50 amp socket is fed directly from the breaker and another breaker "out" wire takes the L1 and Neutral go to the 30 amp socket and the L2 and Neutral go to the 20 amp Duplex.
You are welcome to use any combination of outlets, provided the total load does not exceed 50 amps on any circuit leg. For this example, if you are using the 50 amp service on your camper and the L1 camper circuit is pulling 40 amps and you connect another extension cord to the 30 amp socket, any attempt to use more than 10 amps will trip the 50 amp campground breaker.