Trying to figure out if what I'm trying to run below is moving too close to the limits of a 20 amp 120V outlet and limits of a 12 gauge extension cord that is 25 feet.Trying to run a 135K BTU A/C unit on my travel trailer. Connect travel trailer to 30 amp to 20 amp dogboneDogbone connects to 12 gauge extension cord that is 25 feetThat extension cord connects to a 20 amp 120V outlet.Nothing else in the travel trailer is run, no AC to DC converter, microwave etc.First Question: Am I getting too close to the limits of the extension cord and 20 amp outlet?Second Question: Should voltage drop be a concern, since there is approximately 40-50 feet of cable (travel trailer wiring + extension cord) between the outlet and the AC?Using the 80% rating rule, 1920 watts is about the upper limit for a 20 amp service right?Now, to be clear, I have actually tried this already and had no issues running the A/C for 4+ hours with the fan on high and the compressor was engaged for 90% of that time. The extension cord plug into the 20 amp outlet did get a little warm, but not enough to be concerning. None of the breakers ever tripped either.I was not able to directly measure the wattage either, my kilowatt meter is only rated to 1800.

Verify running voltage is 108+ inside the RV and check for excessive heat at the connections.Otherwise you are good to go.

In theory it should be fine but if any one part is questionable, like a worn connection someplace, it will cause heat and you'll have a problem.I would try it for a while and monitor the connections.

Would use a 10 gauge extension cord. You're pretty close to maxed out on the 12. I ran a 13.5K A/C on a 10 gauge 50 foot extension cord to 20 A outlet before I put in my 50 A service. Voltage was down to 112 - 113.

As you have noted it will work and you have checked connections and verified temp increase is not excessive. When I do the same and run our rig's AC here at home I keep an AC voltmeter (Amazon/Ebay for a few bucks) plugged into one of the interior outlets to keep an eye on voltage drop as I don't like to go much lower that 108Vac, don't want to harm compressor with low AC voltage.

I do this all the time with my setup except I do have a heavy duty contractor type extension cord. Its a 10GAUGE type. No issues here with my 13,500btu air conditioner... Those red-oragne extension cords from WALMART are not heavy duty enough to use for this application. Think those are only 14guage cords...I also have one of these RV plug in 120VAC meter that has the safe use scale on it... Pretty handy to have in plain view somewhere making sure my 120VAC is a good safe level to use...Google imageAlso make sure all three conductors are being used with the extension cords. This is the only Earth Ground for your trailer coming from your house reception. I always check with one of those Circuit Testers to be sure the 120VAC receptacle I am using on the house side has the ground connection working... Got mine from LOWES... google imageRoy Ken

Running A/C with extension cord into 20 amp outlet.

26 Replies

TurnThePage
Explorer
Feb 14, 2017
I leave a Kill-o-watt plugged into an outlet in the trailer to monitor voltage. At home, I've noticed that it steadily drops as time goes by. I end up having to shut down after an hour or so as the voltage will drop clear down to 104 VAC. And that's using a 20' 30 amp extension cord.
RoyB
Explorer II
Feb 14, 2017
I do this all the time with my setup except I do have a heavy duty contractor type extension cord. Its a 10GAUGE type. No issues here with my 13,500btu air conditioner... Those red-oragne extension cords from WALMART are not heavy duty enough to use for this application. Think those are only 14guage cords...

I also have one of these RV plug in 120VAC meter that has the safe use scale on it... Pretty handy to have in plain view somewhere making sure my 120VAC is a good safe level to use...

Google image

Also make sure all three conductors are being used with the extension cords. This is the only Earth Ground for your trailer coming from your house reception. I always check with one of those Circuit Testers to be sure the 120VAC receptacle I am using on the house side has the ground connection working... Got mine from LOWES...

google image

Roy Ken
Sandia_Man
Explorer II
Feb 14, 2017
As you have noted it will work and you have checked connections and verified temp increase is not excessive. When I do the same and run our rig's AC here at home I keep an AC voltmeter (Amazon/Ebay for a few bucks) plugged into one of the interior outlets to keep an eye on voltage drop as I don't like to go much lower that 108Vac, don't want to harm compressor with low AC voltage.
STBRetired
Explorer
Feb 14, 2017
Would use a 10 gauge extension cord. You're pretty close to maxed out on the 12. I ran a 13.5K A/C on a 10 gauge 50 foot extension cord to 20 A outlet before I put in my 50 A service. Voltage was down to 112 - 113.
ScottG
Nomad
Feb 14, 2017
In theory it should be fine but if any one part is questionable, like a
worn connection someplace, it will cause heat and you'll have a problem.
I would try it for a while and monitor the connections.
time2roll
Nomad
Feb 14, 2017
Verify running voltage is 108+ inside the RV and check for excessive heat at the connections.
Otherwise you are good to go.

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Running A/C with extension cord into 20 amp outlet.

26 Replies

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