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Old 04-27-2014, 06:15 AM   #15
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1974 31' Sovereign
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 19,574
Most modern air conditioners draw 18 amps to start, and 12-14 amps to run. The problem with longer cords with multiple connections is voltage drop over distance, and through mechanical connections (plugs).
Electrons travel over the outside of the wire, so a thicker wire will carry more electrons, and thus more current. The voltage drop will manifest itself as increased amperage and heat generated. Amps low=volts high, and volts low=amps high. The lowered voltage through thinner, longer runs of wire, with attending voltage loss, is what causes problems such as burning up compressor motors.
So, long-winded response short, as long as the extension cord is large enough to carry the load over the entire run of the connection, you should have no problem.

Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
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Old 04-27-2014, 08:51 AM   #16
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1972 31' Sovereign
Fort Bragg , North Carolina
Join Date: Jun 2011
Posts: 268
As I purchased a 50' 20A HD extension cord last night at Lowes, the one thing I forgot to do was to check the forums and here is the discussion.
We just installed a new Duotherm 15K HP and it will run on an extension cord both AC and heat as long as there is nothing else on the house circuit.
However when I went to turn on the electric function of the A/S refrigerator, the house breaker tripped (15A service). So, there I figured I need to find a 20A service if I wanted to use the electric fridge, not gas while parked at the house.
We also did away with all of the 1156 light bulbs and replaced them with 18 LED puck style lights, and LED equivalent bulbs in reading, mirror lights and rear lights. Side-marker lights are next. Not only was there a huge drop in electric load/demand, but the heat that these 1156 bulbs produced was reduced. This was a 2-year project of buying them and then getting them installed.
I also found this electric flow calculator within this link. Don't know if it will help, but it does give the numbers as Terry stated above based on wire gauge and distance.

American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies and wire breaking strength

I'm for sure getting smarter in these areas thanks to these types of discussions.


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Old 04-27-2014, 09:50 AM   #17
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1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,592
In general, a 30' #10 wire extension cord will not be the real issue, it is the connectors (plug and socket) at the ends of both the AS and the extension cord. By in large, most of the older AS units with the fixed cords have molded plugs on the end. After a time, those plugs become damaged, either mechanically electrically and no longer fit tight when plugged in, or due to poor outlets may have over heated and the prongs out of place slightly, or corroded. I also have cut old ones apart and found the original wire to prong connections made poorly or damaged.

The same thing happens on the extension cord, but the worst is the molded outlet end. It often does not make good contact at all with the trailer plug resulting in high resistance and overheating (and voltage drop). Then the final end plug which goes into the campground outlet has another molded plug, and the outlets are very commonly worn themselves and are another high resistance point.

So, I doubt you will really find the #10 wire to be the problem on a 30 amp system, but the connectors, plugs and outlets, can really cause issues. This can affect both the starting current draw of the AC and the overall voltage drop of the system of cords and plugs you use.

I don't have a real recommendation for a solution other than look for really high quality cord sets, with good plugs and outlets, or make up you own with quality components. Typical extension cord sets available at Wal mart and common RV store stock are not very good over time. Again, the molded outlets seem to be the worst offenders. I have replaced some with metal boxes holding high quality RV outlets that really grip the plug ends of the RV. If your trailer plug is getting tired, with any signs of loose pins or melting at all, replace it with a good quality RV plug (and they are not easy to find).

And complain to the campground owners who don't keep their 30 amp outlets replaced often enough and are loose and worn out. They often will cause your RV plug to melt, if it is a molded on one, because of the poor connection at the post.

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