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Old 08-09-2014, 07:29 AM   #15
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Quote:
Originally Posted by HawkinGal View Post
The little (20 sites) campground at my Michigan sporting club only has 20 amp service.
Just got off the phone with the seller of an '85 Sovereign 29' who says his original Coleman ac doesn't make the trailer cold on 20 amp, ice-cold on 30 amp.
What the seller told you does not reflect Ohms Law. I would be very skeptical.

Appliances like a rooftop AC draw a fixed amount of current in amps. If the campground outlet supplies that amount of amps (or more) it will work fine. If the campground outlet supplies less amps than the A/C needs, the campsite breaker flips off.

It can easily be calculated. Just find the wattage specs for your model A/C.

A Mach 3 13500btu A/C for example specifies wattage as 1595/1924. Watts divided by voltage gives current. So....

1594watts/120volts = 13amps on low
1924watts/120volts = 16amps on high

The 20amp service at your campground would run the Mach 3 and leave a few amps for other things.

If that Mach3 tripped a 20amp breaker at 120v, something is wrong with it.
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Old 08-09-2014, 08:04 AM   #16
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I hesitate to jump in but motors draw a fixed power during operation so if the voltage is low, the amperage draw will increase. Your division is correct but all induction motors will draw much more power, and current, when they start. So a compressor will draw up to 3 times its running current when it starts. It is a momentary draw and if the breaker is rated high enough, it will not trip, risky with a 20 amp breaker circuit, though. In addition, if the circuit cannot provide the voltage needed repeated starts at higher amperage will result in early failure of the compressor motor. I just do not see why people risk their equipment by trying to run AC on a 20 amp circuit.
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Old 08-10-2014, 08:48 AM   #17
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It doesn't seem to struggle and the breaker doesn't trip, can damage still be done? If you put a thirty amp breaker in place of a twenty amp it really doesn't change anything but the amps in witch the breaker trips. The problem would then be the wire size. Thirty amp should have #10 twenty should have # 12. The wire size could restrict the amps/volts. Correct ?
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Old 08-10-2014, 07:48 PM   #18
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I just do not see why people risk their equipment by trying to run AC on a 20 amp circuit.
Larry
Running a 15amp appliance from a 20amp campground circuit is not going to harm it anymore than running it on low voltage from a 30amp campground circuit.

Yes, of course, campground voltage lower than the A/C is rated for will cause a corresponding current increase. The individual circuit breaker in the RV beaker box is there to protect the A/C should current get too high.

If the campground's voltage gets so low that a 15amp rated A/C trips a 20amp campground breaker, moving to a 30amp site will not help. Its voltage will be low too, so then the 20amp breaker inside the RV will trip.
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Old 08-10-2014, 08:45 PM   #19
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It doesn't seem to struggle and the breaker doesn't trip, can damage still be done?
No damage will be done from running an typical 15amp RV A/C from a circuit protected by a 20amp breaker.


Quote:
Originally Posted by 1965 mustang View Post
If you put a thirty amp breaker in place of a twenty amp it really doesn't change anything but the amps in witch the breaker trips.
Basically you are correct but you really would not want to do that unless you first verified that the circuit wire was large enough to handle the higher current the 30amp breaker would permit to flow. If not the wire will heat up and could melt/burn. It is very likely that the wire size of a circuit with a 20amp breaker was sized to handle 20amps max.

You can however put a 20amp breaker on the larger wire sized for a 30amp circuit breaker.

Quote:
Originally Posted by 1965 mustang View Post
Thirty amp should have #10 twenty should have # 12.
Usually.

Quote:
Originally Posted by 1965 mustang View Post
The wire size could restrict the amps/volts. Correct ?
Wire has resistance so it always restricts current and lowers voltage. Wires are sized large enough that the resistance is negligible over the short distances used in buildings and RVs. If you pull more current than a wire was sized for, that resistance causes excessive heat. In such a case, the breaker is to be matched to the wire so it trips before the wire gets hot.
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Old 08-10-2014, 09:07 PM   #20
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Use a voltmeter. If you read 110 volts inside your AS or higher with AC on then you should be okay. If lower then turn the AC off and save it from burning out.
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Old 08-10-2014, 09:31 PM   #21
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I have a plug in watt meter that reads voltage, something like this one at Amazon: Amazon.com: P3 International P4460 Kill A Watt EZ Electricity Usage Monitor: Home Improvement

and my surge protector will disconnect if the voltage goes too low. The watt meter is ore convenient because you can just plug it in and leave it there instead of using a DVM.

Circuit breakers have a published curve: a 20 amp may let 30 or 40 amps through for a short time, then the 20 amp can be regarded as steady-state protection.

BTW, circuit breakers do get "tired" if they are used a lot, and will tend to open at a lower current than original. If the voltage looks good and the breaker still opens then try replacing it.
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