Hi Mike, I need to add a 25-foot extension cord to my shore power cord to reach the outlet in my garage while my RV is parked in the driveway. I don’t need 50 amps since this is just for charging the batteries and running the air conditioner when the kids want to hang out in the RV. I was going to get a 20-amp to 50-amp adapter and an extension cord, but there’s a lot of price difference between the orange cords I can get at Home Depot and the heavy black cords from the RV stores. Why is there such a price difference, and just how do I pick the right extension cord. I love your articles, and keep up the good work. —Steve
Hi Steve, Glad you like my articles, and I’m happy that you’re asking these questions before you get into trouble. No, not all extension cords are created equal, and here’s why. It all comes down to amperage needed, how much voltage drop you can put up with, and the temperature rise allowed.
So let’s start with a simple 30-amp circuit. As you may know from one of my previous articles, that can provide up to 3,600 watts total (120 volts x 30 amps). Here’s a chart of the wire size needed to pass 30 amperes of current safely.
Let’s say that you do get the cheap orange 16- or 14-gauge extension cord from Home Depot and manage to hook it up to your RV with a series of dog-bone adapters. Looking at the chart you’ll see that a 14-gauge cord is only rated for 15 amperes of current and you’re asking it to pass 30 amperes. Not only will you increase the voltage drop down to less than 110 volts (as low as 100 volts with a long cord), you’ll also get a lot of heating of the extension cord itself, which can be dangerous and a fire hazard. Here’s a video I made of what happens when you overload a 15-amp extension cord with 30 amperes of current.
That’s why you really need at least a 10-gauge extension cord for any 30-amp circuit. As you can see from the chart above, it’s rated for 30 amperes of current so it will have much less voltage drop (easily half as much as a 14 gauge cable with the same current). Plus there will be much less heating.
But there’s more. If you want to run your RV’s air conditioner, it probably won’t even start up properly with a 14-gauge extension cord, especially if there’s any length to it (50 feet or more). There will be way too much voltage drop when the HVAC compressor kicks in, and you’ll probably just have the rotor lock and the motor hum. Not good for the lifespan of the compressor, and not good for your cool factor when hanging out in the heat. Ugh…
I recommend that you get a proper pedestal outlet installed in your garage and a 10-gauge extension cord for a 30-amp circuit or a 6-gauge extension cord for a 50-amp shore power circuit. You’ll pay more up front, but all your RV appliances will operate properly and you won’t worry about getting hot around the collar when it’s time to crank up the air conditioner.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.