The statement “Never plug in with a 20-amp extension cord” can be discounted for several reasons. Books have been written about amperage loads, voltage drop, and undersized extension cords. We don’t have the time or space to cover the nitty gritty* details here, but let’s look at some scenarios and why this statement is inherently wrong.
We can immediately discard this statement as small RVs (folding trailers, truck campers, etc.) and many vintage RVs are only equipped with a 15-amp plug. Therefore, these RVs can utilize a 20-amp extension cord with little concern as the cord is rated for more than the RVs electrical requirements.
Why is using a 20-amp extension cord okay?
Now for a deeper look. For those with 30- and 50-amp electrical service (shore power cords), it is always best practice to use an extension cord rated for the same amperage or higher than your RVs electrical service. Example: Use a 30-amp extension cord for a travel trailer with a 30-amp electrical plug.
However, seasoned RVers with 30- and 50-amp service know that sooner or later they will have no choice but to plug their RV into a lesser-rated electrical outlet. With or without the use of an extension cord, the limitations of doing so must be understood.
Situations where one might have to plug into a 15- or 20-amp outlet include parking in the driveway of a friend or relative’s home (aka “moochdocking”) or an outdated campground.
In these cases, it is still the best practice to use an extension cord with the same or higher amperage rating as your RV, utilizing a park adapter to connect (step down) to the lower-rated outlet. Doing so minimizes voltage drop and maximizes the amount of power available to your RV.
However, if you don’t have an extension cord rated for the same or higher amperage or the one you have is too short to reach the 15- or 20-amp outlet, it is permissible to use a heavy gauged extension cord (12 gauge or heavier). By using a park adapter between your RV shore power cord and the extension cord, the extension cord can then be plugged directly into the outlet.
Keep the following limitations in mind
- Avoid exceeding the amperage rating of the outlet the extension cord is plugged into. If you are not knowledgeable concerning the various power requirements of the appliances in your RV, click here to learn more about amperage draw. If you do happen to exceed the capacity of the outlet, say 22 amps from a 20-amp rated outlet, don’t worry as the circuit breaker protecting the outlet will trip, defending your RV and extension cord from damage. If the circuit breaker trips, just reduce the load in the RV and reset it.
- As mentioned above, voltage drop needs to be taken into consideration when operating on an extension cord. The longer and lighter the extension cord, the more the voltage will drop (decrease) when it arrives at your RV. As the voltage drops, the amperage increases to compensate. With increased amperage comes heat and with heat the potential for melted park adapters, extension cords and charred outlets. The heat will be most pronounced at the connections where resistance is highest. When operating on an extension cord (even 30- and 50-amp cords) it is always a good idea to inspect connection points for heat. If you discover a hot spot, disconnect the power and check the connection points for corrosion and proper contact, and that they are fully connected (plugged in). If this does not correct the problem, discontinue using the cord.
Note regarding voltage drop: While outside the scope of this article, many RVers monitor the voltage inside their RV via an inexpensive plug-in voltmeter like this. Most agree, seeing the voltage drop below 106 volts is cause for concern. Click here to read an informative forum discussion on the topic.
What if the cord is rated for less amperage than the RV and outlet it’s being connected to?
Next, we need to discuss the use of extension cords when the cord is rated for less amperage than the RV and outlet it is being connected to. This is one case where you can’t count on a circuit breaker for protection. Here is one likely scenario. Say you pull into an older state park that only has 30-amp outlets. Unfortunately, the outlet is beyond the reach of your shore power cord by 15 feet. However, you do have a 25-foot 12-gauge (20-amp rated) extension cord with you. Being a prepared RVer, you also have a wide selection of park adapters for any situation you might encounter during your travels. Using your park adapters, you place a 50-amp to 15-amp adapter between your shore power cord and the extension cord you will be using.
You then place a 15-amp to 30-amp adapter between your extension cord and the 30-amp campground outlet and plug everything in.
Here is where things can go wrong. Believing you have 30 amps of power available to your RV, you turn on the electric element on your water heater (12 amps) and then turn on an electric fry pan (10 amps) to cook a meal. Throw in a few lights, the RV’s converter/charger and other incidentals and now you have a load of say 25-26 amps. While you are under the 30-amp rating of the campground outlet and the circuit breakers protecting it, you have grossly exceeded the amperage rating of the extension cord and the 15-amp-rated park adapters hooked to each end of the cord. The results of this scenario are likely to be melted park adapters, cord, and possible fire. Unlike the two earlier examples, the circuit breaker is unlikely to trip in this scenario as the amperage draw never exceeds the 30-amp rating.
It’s false, but…
In conclusion, the statement “Never plug in with a 20-amp extension cord” is false, but there are cases (especially as the last scenario demonstrates) where you need to fully understand the limitations of using one to maintain safety.
Next time you find yourself moochdocking at a friend’s or relative’s house, feel free to accept their hospitality of them “throwing you a line” of 15-amp service. Just understand what you can and can’t do with the limited power available. The easiest thing to do is just pretend you are dry camping. The 15 amps are more than sufficient to keep your house batteries charged while you operate your propane furnace, water pump, absorption refrigerator on gas and a few lights for the evening. Heck, there is probably enough to operate your 120-volt TV too!
Remember these words of wisdom from electricity expert Mike Sokol, “OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.”
Be smart and enjoy!
“*” The nitty gritty: While this article could have been written from an electrician’s point of view, the author attempted to use laymen’s terms that most RVtravel.com readers can understand. Those of you with advanced electrical knowledge are free to share more in-depth information via the comment section below.
Now, some questions for you:
- Is there a reoccurring half-truth you keep seeing online that you would like to see addressed?
- Were you taught something by other RVers that turned out to be bad advice?
- Have you recently read something that left you wondering, is that true?
Please share your comments using the comment box below and we will do our best to provide the facts in a future entry.
Lower amperage to your RV is absolutely safe as long as the circuit breaker is the “weak” link in your circuit. For heavy loads, always use an extension cord rated at, or higher than the breaker protecting the circuit, e.g., 50 amp RV > 20 amp cord > 15 amp breaker. Any excessive demand will open the breaker before reaching your cords failure point.
Keep in mind that any ?? amp rated wire/extension cord is not rated to carry that current continuously. Typically 80% is the maximum for continuous use and even then the cord will be surprisingly warm to the touch.
Ey only follow the electrical advice from “Just Ask Mike.”
I’m not saying one doesn’t exist but I’m certainly not familiar with any AWG12 extension cord that is rated for 20A. Maybe a 5 or 10 footer. I always use, have on board, AWG 10, @50′ which is good for 20A.
My Victron power management system will allow me to dial down the available amps so my system will add inverter power along with my incoming power. So no harm for the cord or outlet. Love it!
We’ve plugged into home circuits many times, (never really sure if 15A or 20A). Usually it’s not a problem. We do have to watch out for and be careful regarding running the A/C. It’s OK if it is cycling off then back on periodically. Gets more dicey if it wants to run for hours (hot summer day, in the sun). We have a 30A Class C.
The recurring half-truth (actually it’s NOT true at all) that makes me nuts is the one you promulgated in this morning’s article on trailer brakes – that you become illegal if you drive your RV into a state with more stringent trailer brake requirements than yours, unless your RV meets that other state’s rules. NOT TRUE, gents. Similarly with licenses. If you’re licensed to drive your rig in YOUR state, you’re legal in any state. If your RV meets YOUR state brake requirements, it meets them all. Reciprocity applies, gents. PLEASE stop spreading incorrect information.
20A extension cords are not the kind sold at Walmart, those are 15A. You have to search for 20A at electrical suppliers.
A quick Google will give you numerous 10Ga extension cords available from Amazon, and Big Box stores, Even Harbor freight has 10G which according to the charts on Amp limits like this one
and wire length can be good for up to 50′ if you only need 20 Amp.
I’ve use a 20A extension cord for my 50A RV. But only if I’m basically just maintaining the batteries. And I’m always plugged into a EMS, no matter what cord I’m using. The 20A can work but can be iffy. Any bigger current draw, then while maintaining batteries, will likely trip the GFCI, that should be in place for either garage or outdoor use. If I’m planning on doing anything inside, I use a 10AWG wire extension cord.