The 120 Volt RV Electrical System is identical to household electricity. Similar wall sockets and circuit breakers are used in RV’s. This power comes from a number of sources that include the campground pedestal, your inverter (if so equipped), and your on-board generator (if so equipped.)
120 Volt RV Electrical System and RV Park Power
The more modern campground pedestals will usually have three types of plugs; one 20 amp receptacle that looks like a household outlet, a 30 amp receptacle for RV’s that require 30 amp power, and a 50 amp receptacle for larger rigs that require 50 amp power. A very small trailer or pop-up that doesn’t have an air conditioner can use the 20 amp plug. Larger travel trailers and some small 5th wheel trailers and some motorhomes are wired for 30 amp power. These rigs usually have only 1 air conditioner. Some have 2 air conditioners, but must use only one at a time. The rigs wired for 50 amp power usually have at least 2 air conditioners and need this level of power for the AC powered on-board systems.
There are adapters available in case the park only has 20 amp or 30 amp power. You can certainly run any RV on 20 amps, but you will only be able to use one or at the maximum 2 appliances. It is not recommended to try to run an air conditioner on 20 amp power. There are adapters to run a 50 amp rig on 30 amp power with reduced capacity. Only one air conditioner at a time with that configuration. There are also adapters to run a 30 amp rig on a 50 amp receptacle, but you will still only have 30 amps available to the rig on only one leg of the 50 amp circuit.
30 Amp Park power to 50 Amp RV power cable 
50 Amp park power to 30 Amp RV power cable
AC Power Circuits
A 120 Volt RV Electrical System AC circuit requires at least 3 prongs in the receptacle. One is the ground, one is the hot 120 volt wire, and the other is the 120 volt return wire. 30 amp circuits have heavier wire and thicker terminals in the plug and receptacle to handle the increased current. The 50 amp circuit has a 4 pronged plug. Again one is the ground terminal, there are 2 120 volt hot terminals, and there is a common 120 volt return terminal. The 50 amp circuit has even heavier and thicker wire to handle the increased current. Each leg of a 50 amp circuit is a 50 amp 120 volt circuit, so actually you have a total of 100 amps supplied to the RV.
Here are some of the appliances that use 120-volts:
- Air conditioner
- Microwave oven
- Refrigerator(if a residential unit)
- Satellite Receiver
- Television
- Household appliances
- Converter
The Converter
We covered converters in the 12 volt DC chapter, but the converter converts 120 volts AC to12 volts DC. When your RV is powered up by campground power, both 12 volts DC and 120 volts AC are provided by the campground receptacle.
Circuit Breakers
Where we had many fuses protecting the 12 volt DC circuits, the 120 Volt RV Electrical System circuits have re-settable circuit breakers very similar to the ones found in a home breaker box. Manufacturers locate the breaker panel in all kinds of places and it’s a good idea to locate it in case a circuit becomes overloaded and trips a breaker. In our rig, there are even 2 circuit breakers located on the inverter that powers the microwave and the bathroom and kitchen Ground Fault Interrupter(GFI) circuit GFI outlets are usually located near sources of water and will trip when it sees a near short. The circuit breakers can usually be found behind a metal panel, close to where the power cord enters the RV. Make it a point to familiarize yourself with the circuits and label them.
Common Campground Electrical Problems
Many older campground electrical receptacles are cracked, and discolored from too much heat. Plugging in to one of these causes a poor connection which will cause heat build-up to the point that it can melt your power connector. If your connector has warped and corroded blades, the same situation exists. A little steel wool and some elbow grease will prevent this condition.
Sometimes a campground outlet will be miswired. We use an inexpensive electrical circuit analyzer available at hardware stores and camping supply stores for less than $10. Plug this analyzer into the 20 amp receptacle and look at the lights on the analyzer and compare the pattern to the chart on the front of the analyzer. You will quickly know if the circuit is properly wired. Use a 30 amp to 20 amp adapter and plug the analyzer in to the 30 amp receptacle and repeat. You will need a volt-meter to check the 50 amp receptacle. Notify the campground office immediately if you find a problem and do not plug your rig in until the problem is fixed or find another site and do the checks all over again.
If the analyzer shows reversed hot and ground wires, you have a “Hot skin” condition and electrical shock is likely if you touch the rig while standing on the ground. Change sites immediately. There is an inexpensive tool every RVer should have handy to check for this “Hot Skin” condition. It is a non-contact AC voltage detector and is available at most hardware stores for around $20. Take the detector outside and while standing on the ground, touch any metallic part of the RV with the tip of the detector. If it flashes or emits a sound, you have “Hot Skin” and must carefully remove the rigs power plug and find another site.
Quite often, especially with 30 amp power, the campground receptacle will have a “Nervous” breaker that will trip for no apparent reason. Breakers do age and get weak with age and high current running through it. The campground maintenance personnel can very easily replace that “nervous” breaker and restore reliable power to your rig. Sometimes the trick is to convince the campground folks that that is the case.
There is a great book by RV power expert Mile Sokol called “The No-Shock Zone”. Here is his very informative website http://www.noshockzone.org/15/
Electrical Surges and Surge Protectors
Any power line can be subject to surges(over voltage above 130 volts) and sags(under voltages below 100 volts.) These conditions can damage the electronics in many appliances, televisions, and other sensitive RV electronics. Enter the Surge Protector, otherwise called the Energy Management System These protective devices plug into the park power and the rig power plug is inserted into the surge protector. Internal circuits in the surge protector will remove power to the rig when incoming voltage exceeds the hi or lo set points built in to the protector. After a time delay, power will be sampled for good voltage and power will be reapplied to the rig. Many of the better units have testing circuitry that will sample the power at the pedestal and analyze it for proper wiring connections before power will be applied to the rig. Indicator lights or even remote control panels will keep you informed of what is going on. We recommend that ever rig be protected with an appropriately sized surge protector. It will keep you from loosing thousands of dollars worth of electronics in your rig.
Hard-wired surge protector with remote 
Pedestal mounted surge protector
Inverters
Another source of 120 volt AC power is the inverter that converts 12 volts DC from your batteries to 120 volt AC. These inverters can be stand alone devices, or they can contain the inverter, converter, and a 3 stage battery charger all in one box. Older inverters produce what is known as “Modified Sine Wave” output. Household current looks like a continuous ocean wave with peaks and valleys of the same size with smooth rounded tops and bottoms. the modified sine-wave inverter produces power that looks like the tops and bottoms are chopped off and become flat. This type of power is fine for most appliances, but modern electronic devices can fail over time by being powered by this type of power. Available now are pure sine-wave inverters that produce smooth household type power. If you have a residential refrigerator, you probably have a pure sine-wave inverter. The older units can be replaced, sometimes by drop-in replacements to save newer sensitive electronics.
Modified Sinewave Inverter 
Pure Sinewave Inverter
RV Generators
The third source of 120 volt AC power is the generator. These are measured by how many thousands of watts(kilowatts) are produced. Our diesel motorhome has a 7.5 kilowatt generator. This allows us to use appliances that total 7,500 watts. We can run both air conditioners and the microwave at the same time.
Some generators run with LP gas as the fuel. Once the tank is empty, no more generator. The bulk of RV generators run off of either gasoline or diesel fuel provided by the rig’s fuel tank. Most of these are set up with the fuel line going into the tank about a third of the way up, so you will have fuel to start your rig and go and get more fuel.
Many rigs with generators will have an “Automatic Transfer Switch” that routes park power off and generator power on when the generator is running. When the generator is stopped, the rig will revert to park power by virtue of relays opening and closing in the automatic transfer switch. In those rigs not equipped with an automatic transfer switch, the main power plug must be removed from the park pedestal and inserted in the generator receptacle inside the rig electrical bay so that generator power can flow inside the rig. For park power, the plug must be removed from the generator receptacle and reinserted into the park pedestal.