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RV Basics: 120-Volt AC Systems
By Jan Kuderna

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All RVs have two separate electrical systems: 12-volt direct current (DC) and 120-volt alternating current (AC). The 120-volt system is the same as household electricity, with the same type of circuit breakers, wiring and receptacles. Campground hook-ups often have three receptacles: 20, 30 and 50 amps.

To understand the difference, let’s first define current and voltage. Current is the movement of electrons along a wire. Voltage is the force that moves the electrons.

Obviously, 120 volts is a greater force than 12 volts. Current (the flow of electrons) is measured in amperes, or amps for short. RVs need 20-, 30- or 50-amp hook-ups depending on how much electricity the on-board appliances use. A small trailer or pop-up without an air conditioner can easily get by on 20 amps. A 30-amp circuit is necessary for RVs with one air conditioner. Larger rigs that have 2 air conditioners need 50 amps.

The plugs for 20 and 30 amps are 3-pronged; the 50-amp plug has 4 prongs. This is because the 50-amp receptacle actually conducts two 120-volt circuits in order to supply the 50 amps that big rigs need. In effect, it is a 240-volt receptacle, like those used for electric clothes dryers in a house. RVs with two air conditioners need the 50-amp circuit in order to run both air conditioners at the same time, because each air conditioner runs on a separate 120-volt circuit.

Some older campgrounds may only have a 20-amp receptacle, while some newer campgrounds are being built with only a 50-amp receptacle. Adapters are available that will allow you to hook up your RV to any campground receptacle regardless of what type of plug is on the RV power cord. Of course, you are limited to the available amperage at the receptacle. A 20-amp receptacle will limit the number of appliances that can be run at the same time and may not be sufficient to run an air conditioner. An RV that has a 50-amp plug may find that only one air conditioner will operate if plugged into a 30-amp receptacle.

If your RV is connected to a receptacle that is higher than what is required (for example, when a 30-amp power cord with an adapter is plugged into a 50-amp receptacle), you must limit your electrical usage to 30 amps at any one time. Even though 50 amps are available, the main circuit breaker will trip if the RV is pulling more than 30 amps.
The following appliances use 120-volts.

·Air conditioner
·Microwave oven
·Satellite Dish Receiver
·Anything that plugs into a household receptacle (toaster, coffeemaker, TV, etc)

What’s a Converter?
A converter takes 120-volt AC electricity and converts it into 12-volt DC electricity. This is used to recharge the battery and provide power for lights and other 12-volt appliances. When an RV is plugged into an electrical post at a campground, both systems are running off the campground receptacle.

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.

Problems You Might Encounter

REDS (Receptacle Early Death Syndrome) is a condition found at many campgrounds. Campground receptacles are often warped, cracked, and discolored from excessive heat. When you plug your RV power cord into such a receptacle, a poor connection is made which results in heat, so much heat that it can melt your plug housing or corrode the blades. Corroded blades plugged into the next campground receptacle make a poor connection and perpetuate the problem. Keeping your RV power cord plug clean and shiny with steel wool or a small wire brush will help to prevent REDS.

Occasionally, campground electrical posts are wired incorrectly or do not have a good ground. Inexpensive circuit analyzers, with three indicator lights, can be plugged into an inside receptacle to check for correct wiring. Note which of the three lights are on and check them against the chart on the analyzer housing. It’s wise to check the wiring before plugging in any electronic equipment, such as a computer, since faulty wiring could damage the electronics. If there is a problem, notify the campground office and move to another site.

If the analyzer shows reversed positive ("hot") and ground wires, a dangerous situation exists. In most RVs the chassis is grounded, so if the wiring is reversed, any metal on the RV is “hot.” Carefully unplug the power cord without touching any metal on the RV or the electrical post and move to another site.

Anything with an electronic circuit board (computers, refrigerators, microwave ovens, etc) can be damaged by voltage surges (spikes). A surge protector is a good investment to protect sensitive electronic equipment, especially computers and printers, from damage due to fluctuating power sources. Most surge protectors are built into a power strip for use indoors. Heavy-duty surge protectors are available to protect the whole RV. These are either plugged into the campground electrical post or are permanently installed in the RV.

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