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Old 08-14-2015, 04:47 PM   #1
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Wire gauges and distances question.

I may need to run a 30 amp extension cord into my 50amp cable.

I know I'm limited to one a/c and some other stuff. that's okay. this is only temporary.

However most 30 amp extension cords are 10ga wire. I will be using a 50' extension cord on top of the already 25' 50 amp cable the trailer came with and if I recall correctly anything 30 amp longer than 50' needs to be at minimum 8ga.

I'm having trouble finding an 8ga 30 amp extension cord . Or do you think I would be okay?

Thanks in advance
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Old 08-21-2015, 03:40 PM   #2
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The "troubles" from using under-sized wires are:

1) excessive voltage drop

2) over-heating of wires (fire hazard)

You will usually run into #1 long before you run into #2 unless the run distance is quite short.

Wire has a resistance value per foot. Larger wire has less resistance per foot. I believe your 50 amp cable is 6 gauge wire, and will have about half the resistance per foot of the 30 amp (10 gauge) extension cord.

You should have no issues, especially if your load is significantly less than the full 30 amps. However, good clean contact at the plugs is essential when we are talking this kind of current. Monitor plugs and cords for any indication of getting detectably beyond ambient temperature - a hand check is sufficient.

If you really want to be thorough, check the voltages at the load while the load is running. If you have less than 110 volts, you have too much voltage drop. But the load has to be running for the voltage drop check to be valid.

Fred W
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Old 08-21-2015, 03:53 PM   #3
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Here is a link to one of the available calculators. Will give you a suggested wire size for the length required.

https://www.colemanair.us/vp_asp/Scr...5_WireSize.htm

Assuming a 5% voltage drop is OK (120 V Nominal, 6 V Drop at 30 amps), 10 gauge looks to be acceptable for a 75' run). You should be even better, cause 25' of your run is 50 amp.
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Old 08-21-2015, 03:55 PM   #4
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Another question: I am getting a 30 amp setup at home next Tuesday in the carport.
When the camper is up in the driveway. I will need to use my camper cord plus my 30 amp extension cord ( about 40 feet total distance ) when I want to use A/C , frig overnight. Will this affect the gauge wiring used to wire my home for this use?
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Old 08-21-2015, 04:03 PM   #5
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My suggestion would be to buy a 50' 50 amp RV cord or two 25' 50 amp RV cords. That way you eliminate the possibility of having too small a cord.

At 120 volts 50 amps 75' of #6 cord will have a voltage drop of 3.7 volts. at 30 amps that same cord will have a voltage drop of 3.5 volts.

50' of #10 cord at 30 amps will have a voltage drop of 3.7 volts and 25' of #6 cord will have a voltage drop of 1.5 volts for a total of 5.2 volts.
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Old 08-21-2015, 04:09 PM   #6
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I have a 30 amp system planned for the house. Would my planned setup with 40 ft of 30 amp cord be sufficient to chill the frig overnight before a trip, or to use the A/C by itself during the day for general cleanup purposes? The rest of the time, the camper will sit closed in the carport with a hookup periodically to keep the battery topped off.
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Old 08-21-2015, 04:16 PM   #7
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DobeFanatic -- Are you adding a 40' extension cord to the cord already on the camper? If so then you'll have about 70' of #10 wire total from the receptacle to the RV. The voltage drop will be 5.2 volts for 30 amps. If you only use 20 amps it'll be 3.5 volts so you should be ok with just the A/C and fridge. If you use a vacuum cleaner and the A/C you'll likely be really close to 30 amps.
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Old 08-21-2015, 04:24 PM   #8
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I am using the standard 30 amp rv cord ( is it 20 ft? ), then would add the extension, it measures 40 ft of 30 amp ( didn't realize it was that long ). So that is 60 ft from camper to outlet. Maybe I should ask electrician to install 50 amp service? then use an adapter down to 30 amp?
I use a small hand held vac, not the house vacuum.
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Old 08-21-2015, 04:32 PM   #9
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At 60' and 30 amps the voltage drop will be 4.5 volts or about 3.7% which is fine.

Unless you're planning on doing a serious upgrade to your RV in the next little while, I wouldn't go as far installing 50 amp service.
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Old 08-21-2015, 04:39 PM   #10
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Thanks, I don't want to pay the electrician only to find later that I needed more service for a home hookup.
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