There are two types of electricity in a recreational vehicle, 120 Volt AC power (just like your house) and 12 Volt DC (battery) power. This article will focus on the 120 Volt AC systems. The 120VAC system in a motorhome or trailer works essentially the same as that in your home with the exception of having a removable cord to plug it into the grid. 120VAC typically runs the higher power devices such as air conditioners, residential refrigerators, microwaves and electric hot water heaters.

Recreational Vehicle AC Power Sources

Shore Power

Although it sounds like a nautical term, shore power is what most RVers call the power that comes from the electrical post in an RV park or campground.  Most modern campgrounds have 20, 30 and 50-amp outlets available with 30 and 50 amp being the most commonly used for trailer or motorhome connections.  The largest consumer of electricity is almost always the air conditioner and the number of those required to cool a unit usually drives whether it has a 30 or 50-amp service. One AC unit, 30-amps, two units 50-amp service. Be aware that while the 30-amp RV service delivers 30 amps of power at 120VAC, a 50-amp RV service is actually 50-amps at 240VAC which is actually split into two 50-amp 120VAC circuits, so you actually get 100-amps available in your RV.

You need to know that the 30-amp power connection on a trailer or motorhome is not the same as the 30-amp dryer outlet you may have in your home. RV 30-amp connections are actually wired up to deliver 120VAC power to the RV while a household dryer connection is normally wired up to deliver 240VAC power so even if the RV cord fits a dryer connection, if you plug your camper into a standard drier outlet you’ll be sending double the power into the RV, likely damaging its electrical system (or your home’s) or even worse causing a fire. You can get an adapter to take your RVs 30-amp plug down to a standard three-prong 20 amp one. That should allow you to run almost everything in your unit with the possible exception of the air conditioner.

Whatever size service you have, when setting up at a camp site connection is the same.  A heavy-duty power cord plugs into (or is built into) the RV and then plugged into the proper receptacle on the camp site post. If 50 amps are available there is almost always a separate 30-amp receptacle. You can get an adapter to allow you to plug a 50 amp cord into a 30 amp receptacle if you can’t get a 50 amp site, but you should never try to plug a 30 amp cord into a 50 amp receptacle because in that case the breaker in the campground post will be oversized and not protect you from a potential dangerous overload in your 30 amp cord. If you do plug your 50 amp RV into 30 amp service you’ll likely need to watch the number of appliances you use simultaneously to avoid tripping the breaker at the post. You almost certainly won’t be able to run two air conditioners at a time.

Depending on the age, design and condition of a campground’s wiring it’s common to have voltage spikes, overvoltage, reverse polarity and a number of other issues that can cause damage to your RV’s electrical system or appliances.  An Electrical Management System (EMS) is a combination surge suppressor and power monitor that can detect many of these issues and either issue a warning message or shut off electricity to the RV depending on the severity of the situation. Most RVs on the market do not include an EMS as standard or an option, so it’s up to the owner add one. There are two ways to go here, either a unit that’s hard-wired into the RV’s electrical circuits or one that plugs into the power pedestal at the campsite.

An EMS will run about $100-$200 depending on exactly what options you want and we strongly recommend adding one to your camper’s setup. Basic models include surge suppression and LEDs to indicate the status of the pedestal power while more expensive advanced models have digital displays and will disconnect power if certain fault conditions are detected.

RV Generator Power

Most motorhomes and some fifth wheels and travel trailers have built-in generators wired in parallel with the shore power cable that are capable of running nearly everything in the RV including air conditioners. You can also plug your RV into a portable generator in the same way you plug into shore power. Generators are typically rated in watts(W) or kilowatts (kW) and a 30-amp RV will require a 3600-watt (3.6kW) generator while to run everything in a 50-amp unit will need a 12kW generator if you want to be able to have the same total of 100-amps available as when connected to shore power. When using a generator you essentially have the same 120VAC power you’d have on shore power.

Built-in generators in motorhomes can be set up to run on either propane or gasoline/diesel fuel tapped from the main fuel tank. In the case of generators running off of the main fuel tank there is usually a level switch that will not allow the generator to be run if the tank gets below ¼ full to eliminate the possibility of running the tank to empty with the generator and being unable to move the motorhome.

 If your trailer or motorhome does not have a built-in generator you can always plug it into a portable generator. Honda and Yamaha are two of the more popular brands. Most of the more advanced generators on the market are capable of provided clean power using inverter technology and some can be combined to proved more power. In choosing a portable generator it’s important to consider their noise level. Choosing a model that meets US National Forest Service noise requirements will be appreciated by you and your neighbors.

DC-AC Inverters

If you want to run 120VAC devices without either shore power or a generator, you need an inverter. An inverter takes DC power from your batteries and using electronic circuitry turns it into 120VAC power. Inverters are rated in watts ranging from 100 or so watts up to 10,000 watts. A 1,500 watt inverter will power a small microwave or hair dryer while larger ones can power a whole RV, but you need to remember that they need a lot of current from the batteries to power those devices. A 1,500 watt microwave will need about 125 amps of current at 12V, not a big deal if you’re just heating up leftovers for a few minutes, but you need to think about your battery capacity before you try to run it too long. Forget about running your air conditioner off an inverter. An air conditioner would draw over 200 amps meaning to run one for a day would require a bank of around 50 100 amp-hour batteries.

Inverters come in two types, modified sine wave and pure sine wave. Pure sine wave inverters generate a waveform that is similar to what comes from your power company and will power almost any type of device. They cost more than modified sine wave ones. Modified sine wave inverters produce an approximation of a sine wave as a series of square steps. Modified sine wave inverters are usually best for powering less sensitive loads like lights or fans. Computers, laptops or cell phone chargers may not run so well on modified sine wave units and require a pure sine wave.

We have more posts on RV electrical systems:

Overview of RV electrical systems.