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.

[time2roll]

I would worry far more about running voltage as long as the startup is reasonable and consistent.

[road-runner]

I find it interesting that in one thread a reduced startup voltage will damage the compressor, while in another thread a current-limiting device like the Micro-Air Easy Start Soft Starter Kit is a good thing. Yes, I know one is limiting average current via PWM, and the other via resistance, and the PWM method is more efficient. Yet they are both limiting startup power, thus startup torque, increasing the amount of time for the compressor to reach full speed. I'd love to see an authoritative explanation how one situation harms the compressor and the other doesn't.

[mustanglover32]

SoundGuy wrote:

DutchmenSport wrote:
In your case, the most that will happen is, your wires will begin to warm up. If they do, you're drawing too much. Simple answer? Get a heaver extension cord.

Worst case: You pop the breaker in your house! Solution? Turn something off, you've exceeded 20 amps.

Not true. The worst that can happen is you could eventually fry the A/C compressor from excessive voltage drop that is so quick it can't be detected with a DVM. A typical 13,500 BTU A/C has an average LRA (Locked Rotor Amp) rating of ~ 60 amps ... do that often enough over a long length of small gauge cable and a warm cable will be the least of your problems. 😉

So if I understand what you are getting at, you are saying that the voltage drop when the compressor engages is more of a concern? I could certainly believe this would be the case with older A/C units, but mine is a 2015 and comes with integrated capacitors that help reduce the startup strain with the large in-rush of amperage when the compressor engages.

My DVM is reading 125V inside the RV with nothing turned on at my house. With the A/C on high and compressor engaged, I have never seen it drop below 117V.

So glad I bought a DVM too, campground I went to this weekend was largely vacant and voltage was 109V with a 1500W heater plugged in and nothing else!! Talk about significant voltage drop!!

[Dutch_12078]

In addition to other good advice given, I'd also recommend turning off the breaker and pulling the outlet out of the box to make sure it isn't "stab" back wired rather than wired with the screw clamps where there's significantly more surface contact. You might be surprised to see how little actual contact there is in a "stab" wired connection. Scary when high loads are involved...

[SoundGuy]

DutchmenSport wrote:
In your case, the most that will happen is, your wires will begin to warm up. If they do, you're drawing too much. Simple answer? Get a heaver extension cord.

Worst case: You pop the breaker in your house! Solution? Turn something off, you've exceeded 20 amps.

Not true. The worst that can happen is you could eventually fry the A/C compressor from excessive voltage drop that is so quick it can't be detected with a DVM. A typical 13,500 BTU A/C has an average LRA (Locked Rotor Amp) rating of ~ 60 amps ... do that often enough over a long length of small gauge cable and a warm cable will be the least of your problems. 😉

[DutchmenSport]

I ran my 30 amp TT from a 20 amp plug out of my garage for 8 years via one of those orange 100 foot extension cords, purchased from Wall Mart. I have no clue what rating was on it.

I could run the air conditioner in the camper with very little problem. Never blew a breaker, and of course, there was absolutely no other draw on that circuit either. As long as nothing else was turned on in the camper, the air conditioner performed just fine! But if I attempted to run anything else, the orange cord would begin to get warm. And the connections would warm up too.

So, we could run the air conditioner, get the camper cooled down. Then at evening shut it off, turn on the televison and sleep in the camper all summer. We did this for ... what? 8 years.

When we got our Outback, I installed a proper 30 amp RV outlet from the garage. Last Summer, I installed another 30 amp proper RV outlet on the other side of the drive way. (completely separate circuit). Putting in the dedicated 30 amp RV boxex, we can run anything now.

In your case, the most that will happen is, your wires will begin to warm up. If they do, you're drawing too much. Simple answer? Get a heaver extension cord.

Worst case: You pop the breaker in your house! Solution? Turn something off, you've exceeded 20 amps.

Meanwhile, begin planning on installing a true 30 amp service on your house / garage dedicated for your camper and use a proper 30 amp extension cord designed for your camper. The connect box should run about $125 ... give or take a little ... Depending upon how far the wire has to run, plan a couple hundred dollars for wire (and it will probably be less). Run the wire yourself to curtail the cost of an electrician. Call an electrician, have them hook up both ends of the wire, and it will probably be less than a couple hundred dollars for their service. (depending upon where you live).

Then you can use your camper just like at a camp ground and won't have to always question your power usage.

[Chris_Bryant]

I should add a caveat- all of my cords have high quality Hubbell connectors which are replaced regularly.

[time2roll]

theoldwizard1 wrote:

time2roll wrote:
Verify running voltage is 108+ inside the RV and check for excessive heat at the connections.
Otherwise you are good to go.

I would be happier if it was >110V.

Yes and 122 would even be better.
If the voltage measurement is posted we can comment on the actual situation.

Kill-A-Watt will read voltage very easy. Power does not need to go through the device.

[turbojimmy]

DrewE wrote:

turbojimmy wrote:

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.

Heat at the connectors wouldn't necessarily cause the circuit breaker to trip because the circuit breaker is responding to current only. Hot connectors are usually the result of a poor connection somewhere--either between the pins/blades and their receiving contacts, or between the wire and the connector. A poor connection has higher resistance, which means both an observable voltage drop and some power being dissipated at the connection (as heat).

The circuit breaker is sized so as to prevent the wire itself from heating too much due to its inherent resistance. It should keep your 12 gauge extension cord from overheating dangerously (assuming it's not confined in a small area, such as by being coiled, so that the heat can't escape readily, and is undamaged, and isn't running through a campfire...).

If a circuit breaker somehow responded to heat far removed from the breaker, it would make tools like soldering irons a complete impossibility.

You're right - thanks for that. The cord is new, not confined or coiled and does not run through fire. Where the RV is plugged in is on the ground, and when it rains the GFCI will sometimes trip but other than that it's been okay.

One day I'll run a proper, dedicated 30A circuit to it. But it's working for now.

[time2roll]

mustanglover32 wrote:
So, from what I'm gathering, it shouldn't be an issue for the outlet, but I need to get a 10 gauge extension cord.

By that logic, is my 30 to 15 amp dogbone being overloaded also?

Check the running voltage is 108+ in the RV and check for excessive heat at the connections.

You do not need anything extra or to spend a nickle unless you have an issue.

You could probably let the converter run also but let it fully charge the batteries before you turn the air on again. Four hours should be fine and let it roll.

[DrewE]

turbojimmy wrote:

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.

Heat at the connectors wouldn't necessarily cause the circuit breaker to trip because the circuit breaker is responding to current only. Hot connectors are usually the result of a poor connection somewhere--either between the pins/blades and their receiving contacts, or between the wire and the connector. A poor connection has higher resistance, which means both an observable voltage drop and some power being dissipated at the connection (as heat).

The circuit breaker is sized so as to prevent the wire itself from heating too much due to its inherent resistance. It should keep your 12 gauge extension cord from overheating dangerously (assuming it's not confined in a small area, such as by being coiled, so that the heat can't escape readily, and is undamaged, and isn't running through a campfire...).

If a circuit breaker somehow responded to heat far removed from the breaker, it would make tools like soldering irons a complete impossibility.

[westend]

By that logic, is my 30 to 15 amp dogbone being overloaded also?

Maybe. We don't know what's inside it and can't judge if it gets hot or not.

If you had an inexpensive Kill-a-watt meter you could be seeing what is happening, electrically, along the chain of that circuit. The inrush current will be momentary and not measured but the load will be metered.

Yes, a 10 ga cord is better than a 12 ga cord but a good 12 ga cordset should handle the current at those distances.

[theoldwizard1]

mustanglover32 wrote:
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.

Yes, you should be concerned.

time2roll wrote:
Verify running voltage is 108+ inside the RV and check for excessive heat at the connections.
Otherwise you are good to go.

I would be happier if it was >110V.

[mustanglover32]

So, from what I'm gathering, it shouldn't be an issue for the outlet, but I need to get a 10 gauge extension cord.

By that logic, is my 30 to 15 amp dogbone being overloaded also?