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Old 05-19-2016, 07:10 AM   #15
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Our interstate had an 11000 ac unit I believe, we ran ours on 20 amp. We had an early interstate. Worked fine.
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Old 05-19-2016, 07:29 AM   #16
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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.
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Old 05-19-2016, 07:46 AM   #17
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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.


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Old 05-19-2016, 08:46 AM   #18
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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.
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Old 05-19-2016, 10:29 AM   #19
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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.
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Old 05-19-2016, 10:46 AM   #20
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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%.
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Old 05-19-2016, 11:17 AM   #21
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I have tested continuous draws on different circuits, I can state without equivocation that MY circuit breakers do not trip at 80% load.

I am going to have to side with Mark, not only because of my own experience, but because what he states makes a lot of sense and seems to be based in a true understanding of the applicable code.


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Old 05-19-2016, 11:49 AM   #22
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This whole discussion is like many others I have read here.

When engineers design systems, whether they be electrical, mechanical, structural or whatever, they design them with all worst case scenarios taken into account. This is considered by most to be reasonable and prudent practice.

However there will always be the "Hey guys, watch this!!" type of people who will want to push the limits and prove the designers wrong. Because, the designs of most systems are robust, (because of the engineers prudent practices) they often get away with their "look how smart I am" tricks. They then become emboldened, and continue these practices until eventually some (perhaps many) of them will meet with an expensive education on why things are designed in this manner.

The above are my opinions. They are based on many years of observation of humans interacting with devices they feel were designed by other humans who were not as smart as they are.

My advice:

Do what the designer of any product recommends rather than following your instinctual desire to take short cuts. In the long run you will come out ahead.

Ken

P.S. I am a retired air traffic controller. Our standard separation was generally 5 miles and 1,000 feet. I often wonder while reading these discussions, how the shortcut takers would feel if I chose to use 1 mile and 100 feet because I knew it would work.
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Old 05-19-2016, 12:25 PM   #23
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Is 30 amp really needed

You jump to conclusions.

Some of us go around "design" because we work with what we have, and some of us change things different than designed for cookie cutter mass production because we want something different.

Frankly, if there is only one right way of design, why don't all bridges look the same?




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Old 05-19-2016, 12:31 PM   #24
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Is 30 amp really needed

Oh, regarding the question at the top of the thread, it is obvious that the air conditioner CAN run on a 20 amp circuit because that specific air conditioner and virtually all other RV air conditioners run exclusively on a 20 amp breaker in the trailers electric service box, so yes, an RV air conditioner can and DOES run on a 20 amp circuit.

There were lots of posts on here warning that other draws should be limited so not to trip the 20 amp breaker.

It is plain that there ARE qualifiers for this to work out, and the qualifiers were well addressed.




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Old 05-19-2016, 12:49 PM   #25
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You jump to conclusions.

Some of us go around "design" because we work with what we have, and some of us change things different than designed for cookie cutter mass production because we want something different.

Frankly, if there is only one right way of design, why don't all bridges look the same?




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You may be correct that I jumped to some conclusions, but not the one you think.

I didn't really pay attention to who was posting what. So it was not directed to anyone in particular including you. However you are free to take it as you wish. After all it is only my opinion. If I am directing a post to another particular post, I will quote the referenced post.

Regarding bridges; There ae many final appearances, but all bridges are designed to carry a specific predetermined load. What some are suggesting here is that it is OK to built it to carry 2/3 thirds the specified load, because they've built bridges that way and none have yet collapsed.

I still stand by:

Unless one is an engineer or designer and wishes to totally redesign any system, then one shoul read and follow the instructions. It's simply common sense. In my opinion, for anyone to advise someone else to disregard a manufacturer's instructions on engineered systems, because they tried it and it worked is just plain irresponsible. It opens both the individual giving the advice and Airforums to possible liability.

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Old 05-19-2016, 01:24 PM   #26
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Is 30 amp really needed

Save the ancient Armstrong A/C that came with my trailer, I "reengineered" everything. Every system, every wire, even my axle placement.

Respectfully, whether any of what I wrote above matters or not is moot, because separate from any opinion, even your air conditioner (if you have one), runs on a 20 amp breaker.

The question was whether a 30 amp circuit is NEEDED to run his AC, the answer is obviously no.

(FWIW, Wally himself was not an engineer)

FWIW X2, I take no personal offense whatsoever when I debate, I endeavor to debate the issue, not the person. No heartburn on my behalf)


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Old 05-19-2016, 01:51 PM   #27
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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?
Yes, size of wire and distance from main source, will you be the only one in control of the switches
New connections will not have as much loss as old corroded fittings, so AS CTA by going one step up from minimum need. In mine they put 30 amps and two A/C's but to protect the system only one could be used at a time by throwing a switch in the system. I moved up to 50 amps 220 volts but still only try to use less than 30 on each circuit with an eye on installed meter. One other thing you can do is take the temperature of the wire and connections when in use, just before they smoke they will show a higher temp. than ambient air.
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Old 05-19-2016, 02:18 PM   #28
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Yes, size of wire and distance from main source, will you be the only one in control of the switches
No, but the few times when we've needed to do this, everyone has understood the situation (i.e it's HOT and we NEED air conditioning) and knew not to plug in anything more heavy than a cell phone charger. Lights are another matter -- run off of house batteries, and LED in any case.

Honestly, I'm far less concerned about running the AC with reliable 20 amp service than I am about just being plugged into some of the 30 amp pedestals I have seen. Long overdue thanks to whomever invented the polarity tester and the kill-a-watt.
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