What gauge extension cord?

A fridge in AC mode will draw 5-8 amps and a 14/3 cord will have a 3-4 volt drop which will not cause a problem. Heavier gauge wire is not going to make the fridge run any better. Appliances are designed to run on less than 120 volts AC and can work fine on 116 volts. For example, Atwood refrigerators are designed to operate on 108 to 132 volts AC.

Even going to a 16/3 cord with a 6 amp load the voltage drop is going to be less than 5 volts and the fridge will run fine.

CA Traveler wrote:
12/3 is adequate for the refer.

I agree if we're all talking about a standard RV refrigerator. That circuit only powers a smallish heater coil. If we're talking about a residential refrigerator with a compressor, I would run heavier than a 12/3 for 100'.

Assuming you are plugging into regular 15 amp outlet the #12 wire is fine.

For just the refer the 12-3 should be OK but 10-3 would be better

I kept our Dutchmen and our Springdale plugged in 24 x 7 at home with just an orange construction style electric cord (100 ft) that you'd buy at any Home Depot. Don't know what guage it is, but it did just fine. I kept the batteries charged and the refrigerator operational. We also were adequate for watching television and keeping cell phones plugged in when we slept in it.

Well, when we got our Outback, I installed a 30 amp plug on the side of the garage and purchased 2 - 30 amp RV cords so we can run the air-conditioner and microwave at the same time when driveway camping now.

But if all you want to do is keep the refer operational, I think any construction style extension cord would do. Don't run the air-conditioner with it. It may power up the air conditioner, but the cord will get very hot too. Not good. But no problems just running your circuit board and refer.

12/3 is adequate for the refer.

10/3