By Dave Solberg
This is Part 3 of Dave Solberg’s “Everything you need to know about RVing” series. Today, Dave looks at 120-volt electricity and tells you just about everything you need to know.
- Part 1: Tips to make your first RV trip more enjoyable: Pre-trip preparation
- Part 2: The ABCs of RV terminology: Every word and term you should know as an RVer
In our homes, we plug in the vacuum, heat up cold coffee in the microwave, and turn on the air conditioner without thinking about where that power comes from. It’s easy—it comes from the local municipal company and is wired throughout the house.
In an RV, we use 120-volt AC, 12-volt DC, and even liquid propane (LP) for the various components. It is important to understand what powers what and how much power everything uses.
120-volt electricity
120-volt power is supplied by either the shoreline cord connected to an outside source such as a campground pedestal, or a generator. The power is supplied to a distribution center which has circuit breakers similar to your home. These circuit breakers supply 120-volt power to components such as roof air conditioners, refrigerators, outlets, and other devices.
Simply put, electricity is the flow of electrons through a conductor. Since you cannot actually see electrons or 120-volt electricity, most technical training programs use a water hose analogy. When you connect a water hose to a faucet and turn it on, you can measure three things: the flow rate of the water going through the hose, the pressure of the water, and the size of the hose that can cause resistance.
With electricity, these three components represent amps (the flow rate), voltage (the pressure), and ohms (the resistance). I am not an expert when it comes to electricity, but rather a handyman. Therefore, I rely on explanations from certified electrical experts that I have worked with for years.
RV terms you need to know regarding 120-volt electricity
Volts (pressure)
According to my “go-to guy” Steve, an RVIA-certified master technician that I use for my RV Repair Club videos, initial voltage for residential usage started at 110 volts and increased to 115 volts in the 1930s. By the 1950s, 75% of all household lightbulbs were 120 volts. In 1984, the U.S. standard was 120 volts; however, you will still hear the voltage referred to as 110 or 120 volts.
What makes voltage more confusing for RVers is that it can fluctuate higher and lower than 120 volts at the source. Ideally, you want 120 volts for everything to run efficiently. However, you can operate components with higher or lower voltage in certain situations. The exact highs and lows have been debated quite often, however, and depend on the size of the unit and the number of 120-volt components being used. Steve tells me that he likes to see the voltage between 117-124. But he also recommends an Energy Management Device, which will shut off the power to the rig when it gets too high or too low. More on that later.
Amperes (amps)
This is the flow rate and it is important to understand when it comes to the power requirements of your rig. The typical campground pedestal has three outlets: 20 amp, 30 amp, and 50 amp. They all provide 120-volt power but have limitations to run 120-volt components in your rig. More on that later.
Ohms (resistance)
This is the measure of resistance. Basically, the larger the water hose, the less resistance and more flow.
The two important components to understand for new RVers is what power requirements your components need and how to conduct energy management. Roof air conditioners can draw up to 14 amps at peak performance, so you can’t plug into your garage outlet when preparing for a trip and run both roof air conditioners at the same time. Knowing what the appliances draw and how you are using them is important.
Campground outlets and what they mean
A typical campground pedestal will have a 20-amp outlet for smaller popup and teardrop trailers, a 30-amp three-prong outlet, and a 50-amp four-prong outlet for the “big rigs”. Each outlet should have a dedicated circuit breaker.
Below is a diagram of the various outlets used at a campground and how they are wired. Notice the 50-amp outlet has two 120-volt “legs” with one going to the left side of the distribution center (H1) and the other going to the right (H2). This splits the power so you can run two roof air conditioners and other appliances without overloading the system.
Note: A 50-amp power supply does not provide 240-volt power such as a residential dryer plug. The image shows 240 volts measuring H1 and H2 only.
A traditional 20-amp outlet will have the “T” slot for the neutral plug, as indicated here. If the outlet does not have the “T”, it is most likely a 15-amp outlet, and you will need to do energy management accordingly.
Note: When checking any outlet with a multimeter, the following voltage measurements should be verified.
- Ground – Hot – 120 volts
- Ground – Neutral – 0 volts
- Hot – Neutral – 120 volts
Before plugging into any outside power supply, it is important to check for proper polarity (wiring) and voltage. You can do this with a multimeter or a surge protection device that shows voltage and proper wiring.
Tip: Before plugging or unplugging the cord into a shoreline outlet, shut off the breaker at the box to prevent arcing or plugging into a compromised outlet.
Inspecting your shoreline cord
Inspect your shoreline cord and the campground outlet every time you connect. If the prongs of your shoreline cord are tarnished or corroded, clean them with an approved electrical spray and a small wire brush. I like the CRC Quick Dry (QD) Spray Lube, which you can find on Amazon here.
If your shoreline cord has melted areas around the metal plugs, it is a sign there has been excess heat, typically due to high amp draw. In that case, the shoreline cord should be replaced. If the campground outlet has signs of tarnish, clean the terminals with the QD spray, making sure the circuit breaker is off and there is no power to the outlet.
Tip: If the outlet feels loose or sloppy, the metal connectors have spread apart and are not getting a good connection. That will happen the more cords are plugged in and unplugged. If you have a 30-amp cord and the connection is loose, use a 50- to 30-amp adapter and plug into the 50-amp outlet. They are not used as much and are usually better quality.
RV gadgets for 120-volt electricity
If you bring any other appliance or gadget along for the ride, it is important to know the amp draw to help with energy management. Air fryers, single-use coffee machines, and other new-fangled appliances take a lot of energy and typically will have the amp draw on the data label. You can also use a metering device to measure the amp draw. Simply plug it into an existing outlet, plug the device in and turn it on. You can find one on Amazon here.
A quality surge protector or emergency management system (EMS) surge protector will verify proper wiring and voltage. It will also protect your electrical system, and you, from a high-voltage surge from the outside source and also a low-voltage drop that could damage appliances. There are several models available at almost any price range you can imagine. Cheap units have little or no reset capabilities—so once it trips, the unit is done. The higher the Joules, the more it can take the surge and reset. I like the Southwire and Power Watchdog models, as they have been in the industry for years and are very dependable. They also have readouts for the amp draw and voltage.
Most RVs come with a 25-foot shoreline cord; however, that might not be long enough to reach the campground pedestal or other outlet. It is important that you use a proper size extension cord and not just the “heavy duty” cord from the local home improvement store. Your rig has either a 30-amp or 50-amp shoreline cord, and the heavy-duty orange cord is only rated at 15 amps. I would not recommend going any longer than 25 feet with an extension. Make sure the extension cord you purchase has molded ends and is ETL-certified, like this one.
There will be times you will need an adapter for your shoreline cord to plug into an external power source. If you have a 50-amp shoreline cord and the campground only has a 30-amp outlet, you will need a 50- to 30-amp adapter. You may also have a 30-amp shoreline cord and the only adapter that works at the campground pedestal is the 50-amp outlet, so you will need a 30– to 50-amp adapter. And, if you plan to plug into your garage outlet while getting ready for a trip, that is a 20-amp outlet.
Again, you will need the appropriate adapter. It is important to get a quality adapter that is molded and also know your power limits. You cannot plug a 30-amp or 50-amp power cord into a 20-amp residential outlet and use everything. Here is a 50-amp campground pedestal (male) to 30-amp shoreline cord (female) adapter.
This is a 30-amp campground pedestal (male) to 50-amp shoreline cord (female) available on Amazon here.
Depending on your level of expertise and confidence, you will want a few electrical testers, starting with a simple non-contact voltage tester. This allows you to test for power at an appliance, cord, or even outlet without actually touching any hot wires. A good combination is the non-contact tester and ground fault circuit interrupter (GFCI) plug-in tester. You can get them on Amazon here.
A multimeter can be used to test AC voltage, DC voltage, and continuity for checking fuses. The DC setting will allow you to test the voltage in your RV house batteries as well as the charging voltage when plugged into a campground source. You don’t need anything real fancy and expensive, as you will not be testing for that much accuracy. I like this kit from Klein, which has the multimeter with the non-contact voltage tester and GFCI tester available here.
Plugging in at home
Most of us like to bring our rig to the house before a trip to cool things down and pack all our “stuff”. Most garage outlets are 20-amp and typically “ganged” to other outlets for appliances such as air compressors, refrigerators, and other items. It is a good idea to have a certified electrician install a dedicated outlet for your RV even if you are only going to run the refrigerator. When your rig is plugged into any shoreline power, the converter/battery charger is pumping out 13.2 volts and could overload the circuit. If you want to run a roof air conditioner, you will most likely want to install a dedicated 30-amp outlet for your rig.
There is much more to RV electricity. However, knowing the basics of 120-volt electricity and conducting some minor testing before just plugging in is important.
Read more RV electricity articles here.
Read more from Dave here.
RVT1223
We carry a tester similar to the one in the picture, but ours also has a volt meter. It allows you to check the pedestal using a 30 to 15 amp adapter.
A couple quick notes – with direct current (DC) resistance is in Ohms. It is a little different with alternating current (AC) and called impedance which is the average resistance as the current flips-flops within its phase.
You can buy ‘orange cords’ in many power capacities both below and above 15A. Pay close attention to the packaging. Most will list wire gauge (copper thickness – the smaller the gauge the thicker the wire), but also maximum wattage. divide watts by 120 to obtain the maximum amperage. And if the cord is over 25 feet, consider buying a cord with a smaller yet gauge number to handle voltage losses.
The rule in ours is AC, microwave, or water heater, pick one. Only one. Had to learn that the hard way because the geniuses that built ours put the breakers and fuses at the bottom of a wall so I can lay down on the floor with a flashlight to reset a breaker.
A Random Tidbit
When buying a space heater, don’t get hung up on the marketing regarding room size. A more expensive one might say it covers a large room while the less expensive one might not say that.
Look at the wattage.
If both are rated at 1500 watts, both convert the exact same amount of electricity into heat. Why is that? Because both must plug into a 15 amp residential wall outlet without popping the breaker. 1500 watts divided by ~110 volts = 13.6 amps (12.5 amps at 120 volts).
Ditto with microwaves, hair styling tools, electric skillets, air friers, etc. The amount of electricity outlet appliances can convert into heat is limited to under 15 amps or roughly 1500 watts.
Thank you for the discussion, Dave! I benefit from redundancy. That is, I tend to need to read/hear something numerous times before eventually understanding and retaining it. Have a great week and safe travels!