Is 30 amp really needed

[tracenuttall]

I have a 30 amp service set up for my 2012 sport. I've heard you cannot run the AC unit with anything less. I recently turned on my AC unit and checked the amperage when the compressor turns on, the most it draws is 14 amps, and not for very long. My question is why does airstream say the AC unit will be damaged if it is not run on a 30 amp set up?

Trace

[eubank]

Remember that your draw from the AC is not the only thing in the RV drawing current. That's where the crunch comes. If you use other appliances -- especially ones that draw a lot of current like hair dryers, microwaves, electric heaters and others -- then you can rapidly reach the limit. And that can be pretty ugly for a unit that runs a motor like the AC.

For many folks, 30 amps are just fine with just a bit of awareness. Running the AC on less than 30 is tricky, tricky, tricky.


Lynn

[HowieE]

I would suggest the next thing you buy for your Airstream is a plug in volt meter. Low voltage is what will kill the AC compressor. Even with a so called 30 amp service in mid summer on a hot day you may see low voltage and want to turn the AC off. The older AC units came with a low voltage indicator light and I have seen mine on many times in the summer in campgrounds that claim 30 amp service.

Anything below 105 volts is asking for problems.

[J. Morgan]

Airstream is in CYA mode on that one.

You might need 30 Amps to run your whole trailer at once and/or while charging the batteries from a heavy state of discharge, but 30 amps to run the A/C and a few lights etc, no.

I have run my air conditioning on 20 amp circuits daily for months on end.

I have an amp gauge that I built in, running normal lights, television, air conditioner, and a hair dryer at the same time flirts with a 30 amp draw.

Superat stultitia.

[Sjcjr]

Originally Posted by tracenuttall

I have a 30 amp service set up for my 2012 sport. I've heard you cannot run the AC unit with anything less. I recently turned on my AC unit and checked the amperage when the compressor turns on, the most it draws is 14 amps, and not for very long. My question is why does airstream say the AC unit will be damaged if it is not run on a 30 amp set up?

Trace

I have a 30 ft classis. I keep it powered to a Standard ground fault outlet with a 20 amp breaker. My digital volt meter inside the airstream shows 120 volts with nothing else electrically engaged. If I turn on the rear 13.5 AC the voltage meter reads a steady 115 volts, which I'm told is sufficient to run the rear AC. I am reluctant to run the unit for any length of time until I further research the issue. Maybe the experts on this forum can weigh in!

[HowieE]

115 volts is safe to run the AC. There are 2 issues here. Low voltage under 105 and high current over 17 amps. Low voltage will cause motor failure in the compressor after prolonged running. High current will cause the breaker to trip. The second tells you right away. The first just costs a lot of money.

Breakers are designed to trip at about 80% of rated current. If the breaker did not trip on the starting current, higher than running current, it should hold while running. Again it is prolonged running at low voltage that is the problem. This is a silent killer.

[ijustlee]

Watch out when using adapters to plug into a standard 120v outlet. They melt very easy when using any high power devices! . It never hurts to feel the plugs to make sure they are running cool and this is especially true if overnighting in somebodys driveway. Even 30 or 50 amp plugs will get warm if the outlet contacts are a little flakey at an RV site. A plug in volt meter like a kill a watt is nice to have and I used to keep one where my coffee pot plugged in even though it monopolized the outlet. In a lot of locations the voltage from the power company will vary throughout the day, where I live now it goes from 127 down to 108 but averages out to 120 volts.

[Inland RV Center, In]

Originally Posted by tracenuttall

I have a 30 amp service set up for my 2012 sport. I've heard you cannot run the AC unit with anything less. I recently turned on my AC unit and checked the amperage when the compressor turns on, the most it draws is 14 amps, and not for very long. My question is why does airstream say the AC unit will be damaged if it is not run on a 30 amp set up?

Trace

Having the ability to safely draw 30 amps @ 125 volts AC, is a HUGE PLUS.

Airstream strives very hard to provide you with things that are above normal or average, instead of below.

Should the supply voltage drop. t then increases. This is why using a cheap extension cord, can contribute to ruining your AC

Keep in mind, that the UNIVOLT is always in the circuit and always draws some current.

Using the AC becomes very border line, if you also want to use an electric toaster. Some electric frying pans can also draw large amounts of current.

Be thankful, that Airstream strives to go a step ahead, instead of behind.

That's why Airstream has the popularity that it has.

Always a little more, instead of a little less. Works for most everyone.

Andy

[wahoonc]

Originally Posted by tracenuttall

I have a 30 amp service set up for my 2012 sport. I've heard you cannot run the AC unit with anything less. I recently turned on my AC unit and checked the amperage when the compressor turns on, the most it draws is 14 amps, and not for very long. My question is why does airstream say the AC unit will be damaged if it is not run on a 30 amp set up?

Trace

14 amps running, it uses a whole lot more than that starting up. Along with whatever else may be on in the trailer. The converter can grab a good bit of power when you first plug up if the batteries are a bit low. The system is designed for 30 amps, feed it less and your risk damaging something.

Aaron

[Wayne&Sam]

Originally Posted by wahoonc

14 amps running, it uses a whole lot more than that starting up. Along with whatever else may be on in the trailer. The converter can grab a good bit of power when you first plug up if the batteries are a bit low. The system is designed for 30 amps, feed it less and your risk damaging something.

Aaron

14 amps was starting up. They said it dropped very quickly.

[lsbrodsky]

Not possible! Just evidence that many people are less than informed about electricity and electrical appliances. Starting current for induction motor devices like compressors is 3-5 times running current. A 13.5 or 15k BTU AC unit is going to draw far more than 14 on starting surge, but either he or his meter is not seeing it. I would believe 14 running. While it might be fast enough to not trip his breaker, the voltage is going to drop significantly for an instant. I would also wonder about his running voltage.

Larry

[sandlapper]

What is the start up draw and then the run draw of a 15k AC?

Is there or was there such a thing as a 15.5 AC?

Thanks. John

[teagues]

The panel inside my 20' has a 30 amp main breaker feeding 4x 20 amp breakers. One of those is for the air conditioner, another for the converter, and the other two for the electrical outlets.

If the air conditioner tries to draw more than 20 amps, wouldn't it throw its breaker at the panel?

I know, I know, voltage drop, other draws, etc. But if I can supply 20 amps 120V to the trailer (properly rated cord and adapter, good city electric service) and control the other electrical draws (turn off the converter and use the house batteries for DC, remember no to dry my hair, microwave popcorn, or make toast), is there some other problem I am overlooking?

[overlander63]

The air conditioner draws 18 amps at 120 volts, assuming no mechanical or electrical problems. It can be run on a 20 amp circuit, if there is absolutely nothing else on that circuit. Not even the converter.

[xrvr]

Our interstate had an 11000 ac unit I believe, we ran ours on 20 amp. We had an early interstate. Worked fine.

[DanB]

Originally Posted by HowieE

Breakers are designed to trip at about 80% of rated current..

Not too sure about this statement.

Circuits should not be loaded up beyond 80% of the rated breaker. But I don't think a 20amp breaker trips at 16 amp.

Much more goes on to calculate effective protection of 80% and 100% breakers.

[J. Morgan]

Originally Posted by teagues

The panel inside my 20' has a 30 amp main breaker feeding 4x 20 amp breakers. One of those is for the air conditioner, another for the converter, and the other two for the electrical outlets.



If the air conditioner tries to draw more than 20 amps, wouldn't it throw its breaker at the panel?



I know, I know, voltage drop, other draws, etc. But if I can supply 20 amps 120V to the trailer (properly rated cord and adapter, good city electric service) and control the other electrical draws (turn off the converter and use the house batteries for DC, remember no to dry my hair, microwave popcorn, or make toast), is there some other problem I am overlooking?

Nope. You are not overlooking anything.

If and when you cross the magic threshold of too much current draw against a given circuit breaker, the power to your trailer will suddenly move from "on" 20 amps to "off" 0 amps.


Superat stultitia.

[HowieE]

Originally Posted by DanB

Not too sure about this statement.

Circuits should not be loaded up beyond 80% of the rated breaker. But I don't think a 20amp breaker trips at 16 amp.

Much more goes on to calculate effective protection of 80% and 100% breakers.

I may have taken a less technical approach to demonstrate the limits of a breaker. The limit of 80% is a code consideration. More then 80% of 20 amps is not within code. National electrical code states a 20 amp circuits should only be loaded to 80%, or in other words, 16amps in total. The circuit is basically derated to 16amps.

[lewster]

If you remove the outer shroud of your A/C unit, you will find a data plate that contains the model, serial number and electrical specifications of your A/C unit. On that data plate will be the RLA (running load amps) and LRA (locked rotor amps) for the compressor and the RLA for the blower motor. These ratings are stated at the 95ºF reference temperature.

Even with the start capacitor present in the circuit, your compressor will draw an affective 50-60 amps as a transient load on start-up. Once running, the compressor typically draws anywhere from 11 to 14 amps, depending on the size of your A/C unit and the outside ambient temperature. The blower motor adds another 2.5-3.5 amps while running.

These numbers are easily verified with a true RMS rated clamp on ammeter. It is also the quickest and easiest way to determine of your unit has lost refrigerant and is not discharging cold air, as they compressor will not be really working against the pressure of the refrigerant and will show only a 4-6 running amp draw.

[markdoane]

You cannot use the "80% rule" for circuit brakers in this case as that rule only applies to multi outlet branch circuits.
The AC is a single appliance connected to a single overcurrent protection device.
Additionally, the breaker is designed to handle the full continuous current listed on the breaker.
The 80% rule only says that you should not plug in an appliance with more than 80% of the breaker rating to a single outlet on a multi outlet branch circuit.
The branch circuit is not derated to 80%.