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

[mustanglover32]

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 dogbone
Dogbone connects to 12 gauge extension cord that is 25 feet
That 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.

[mustanglover32]

CA Traveler wrote:
I'd use a 10 ga cord or upgrade to 30A cord and circuit. Also is it really a 20A plug on a dedicated CB? Most home circuits are multiple 15A plugs on a 20A CB which means there can be additional loads on the circuit.

Good question, about multiple outlets on the same CB. The 20 amp outlet I have is for my washing machine, but I doubled checked and the CB for that outlet is also tied to an outlet in the garage. I will have to remember to plug anything else into that outlet.

But you are right, I think it would be wise to purchase a 20 amp extension cord.

[turbojimmy]

Chris Bryant wrote:
Voltage is all that matters- I run air conditioners off a 100 foot #12 cable all the time- voltage maintains above 115 volts.

Me too - plugged into a 20A outlet. No issues.

I always check for heat at the ends of the cord but haven't had any issues. I'd like to think if there were enough heat the breaker would trip.

[SoundGuy]

mustanglover32 wrote:
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?

Voltage drop is always a concern, especially since you've forgotten to include loss in the run from the house breaker box to the receptacle from which you're drawing power. The key is unloaded source voltage - if it's a nominal 120 vac at the receptacle as it should be you can easily sustain considerable loss and still see well in excess of 110 vac feeding the A/C with the compressor running. Nothing in your post suggests you've even bothered to check so that would be your first step ... if it is I'd have no issues running the A/C on this circuit.

[Chris_Bryant]

Voltage is all that matters- I run air conditioners off a 100 foot #12 cable all the time- voltage maintains above 115 volts.

[CA_Traveler]

I'd use a 10 ga cord or upgrade to 30A cord and circuit. Also is it really a 20A plug on a dedicated CB? Most home circuits are multiple 15A plugs on a 20A CB which means there can be additional loads on the circuit.

[ctilsie242]

Running watts is one thing. What really kills things is the inrush current when the compressor starts.

If I were doing this for the long haul, I would buy a Magnum Energy Hybrid inverter, just so the A/C's locked rotor amps hit the inverter and battery, which can easily take them, as opposed to a 15-20 amp cord which is not going to like even a brief period of handling 60 amps.

[TurnThePage]

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]

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...

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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...


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Roy Ken

[Sandia_Man]

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]

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]

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]

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