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I’m having some trouble figuring out the difference between my 50-amp RV fifth wheel plug and a 50-amp welder plug. I want to wire up a 50-amp outlet for my RV but have been told by my electrician that my RV is not 240 volts. I understand that each leg on the 50-amp outlet is 120 volts, but why don’t they consider this a 240-volt RV? I’m trying to explain this all to my electrician, but he seems confused. Thanks in advance and hope you can help me out. —David
Here’s a graphic of how the electrical system of your RV is wired. Even though you have 240 volts between Hot 1 and Hot 2, virtually everything in your RV needs only 120 volts to operate. That’s right, the air conditioner(s), microwave, converter/charger, television set, hair dryer and everything else all need 120 volts (in the United States, at least). A neutral connection is needed to carry the balance current back to the center-tap of the power company’s transformer. Without a neutral the 240 volts won’t divide evenly into 120 and 120 volts, but instead will vary wildly depending upon the load on each leg. And the only way to get this to work properly is have a neutral connection in the plug itself. The standard RV plug, a NEMA 14-50 shown on the right, is indeed a 4-wire plug with 2-hots, a neutral, plus a ground wire.
On the other hand, a NEMA 6-50 (pictured on the left), which is the standard welding plug you’re proposing to use, does NOT have a neutral conductor, only 2 hots and a ground. So there’s no way to divide the 240 volts into 120 + 120 volts. Some of the confusion is that 50-amp RV shore power should REALLY be called a 100-amp service since it does supply 50 + 50 amps, which equals up to 100 amps of current draw at 120 volts. NEVER plug your RV shore power cordset into any outlet without a neutral. Very bad things will happen.
Also, be sure to test any outlets installed by an electrician BEFORE you plug your expensive RV into it. I have dozens of emails on file from homeowners and confused electricians who didn’t understand RV wiring and did many thousands of dollars’ worth of damage in seconds. Don’t make me put you in that file…
Here’s a reminder of how 50-amp pedestal outlets need to be wired. Don’t make an expensive mistake even if your electrician says he knows how to wire up your new pedestal. Test any new outlet with a voltmeter BEFORE plugging your RV into it.
As always, all of my graphs and pictures can be downloaded in full size to read or print out simply by clicking on them.
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.