Friday, March 24, 2023


RV plugged into garage outlet. What can, and can’t, I run?

Dear Dave,
I’m going to park my RV and hook it up to a garage outlet. I want to run my two rooftop A/C units, my 4-door refrigerator and my RV’s indoor lights. Is this enough amps to do this? —Ben, 2003 Monaco Knight, 34 feet

Dear Ben,
A typical garage outlet is only 20 amps and usually has other outlets “ganged” to it.

Roof air conditioners draw 14 amps each

Your roof air conditioners will draw about 14 amps each at peak, so that puts you over without using anything else! While you are plugged in, the converter will be charging the batteries periodically at 13.6 volts, then a float charge of a constant 13.2 volts, which could draw another 2-3 amps. Your refrigerator draws about 6–8 amps if it runs on 120-volt power, so you can see how easy it is to overload a circuit. The interior lights will draw 12-volt power from the house batteries, so it will not affect the load on the circuit except during the charging, as mentioned.

If you want to plug the unit into a garage outlet and run both roof air conditioners, you will need to have an electrician install a 30-amp circuit and dedicated outlet. However, even with that, the initial startup of the two air conditioners can overload the circuit, as well, so it is recommended to install a SoftStartRV™ to reduce that spike at the beginning of operation.

It is important to understand what is running and what these components draw, such as an electric water heater. It would also be a good idea to use a Surge Guard to know exactly what you are drawing. And make sure you use a properly rated extension cord if needed, and no longer than 25 feet.

 You might also enjoy this from Dave 

Ask Dave: RV is plugged into 30 amp in a heated garage but engine batteries still die. Why?

Dear Dave,
My RV is plugged into a 30 amp that is located in a heated garage. Today and earlier this year the starter batteries were dead. I left the bay lights on for about 24 hours. I boosted the batteries with the house batteries, started the engine, and then shut the engine down. Then I connected a battery minder to the two starter batteries. After a couple of hours, the red light went out on the minder or tender. I was surprised that it went out so soon. —Denny, 2011 Monaco Camelot 43DFT

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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1 month ago

FYI, the -outlet- in most garages is only rated for 15amps (NEMA 5-15, i.e. the normal “house” outlet.)
Even if the wiring and breaker are 20amps, the OUTLET is only rated for 15amp.

This is why people “melt” the 30/15 amp RV adapter.

This is a VERY common mistake, as shown by the normally knowledgeable author making this mistake.

When I built my garage and shop I actually installed 20amp outlets (NEMA 5-20), even though most of the plugs I plug in are only rated for 15amp.
I also wired in a 30amp for the RV (NEMA 30-TT)

Jim Johnson
1 month ago

I added a 20A GFCI circuit on its own breaker outside my home along with a water spigot and I have access to the house sewer line in the same location. Using a Flojet mastication unit, I can park at our curb to service the trailer when we get home and prep it for our next trip. Or… use the trailer as an overflow bedroom with guests.
I can run anything on the RV. What I cannot do with only 20A of AC power is expect to run EVERYTHING the same as we can do at most campgrounds offering full hookups. The 4 biggest power uses are AC, microwave, coffee maker space heater and refrigerator. Pick and choose. Often you can temporarily turn off something long enough to run something else.

1 month ago

A garage should be on a ground fault protected circuit, using my Surge Guard to plug into a ground fault 20 amp receptacle so to run the refrigerator through inverter/converter overnight trips the receptacle every time. I now have a 25 foot 50 amp extension cord that lets me reach the 50 amp receptacle in my barn so I can stay hooked up ready to go. I believe Mike had an article about campgrounds and ground fault 50/30 amp protected circuits a few years ago.

Glenn A
1 month ago

If you’re going to pay an electrician or DIY an outlet, you might as well install a 50A and a 30A. The added cost of materials is negligible once the service call is paid. My .02.

Glenn A
1 month ago
Reply to  Glenn A

Especially since two a/c’s starting are close to the 30A rating .

Thomas D
1 month ago
Reply to  Glenn A

Just put in the 50 amp and get a 50 to 30 amp adapter. It’ll cost you less and I see no need for both. I use the adapter constantly at parks. Never seen a 50 amp plug burnt up but a lot of 30 amp ones

Bob Wallace
1 month ago
Reply to  Glenn A

We agree. We were going to go with a 30A receptacle but went with the 50A. The $ difference was $5 for the different outlet and $20 for the lower gauge/heavier wire. The Time and balance of materials were the same. Now having said that we have a 50A MH. I could run it off of 30A with an adapter, but this made much more sense (to us).

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