By Mike Sokol
Dear Readers,
Since so many of you seem to be backyard camping this summer, or possibly setting up your RV for a COVID-19 medical staff to shelter in place in the RV, I’m getting all kinds of emails about plugging an RV into a 30-amp dryer or even an electric welder outlet. So I’m updating an earlier article about the dangers of miswiring an RV TT-30 outlet with 2-pole 240 volts instead of the correct 1-pole 120 volts.
Dear Mike,
Thank you for bringing the miswiring issue to light. I have been a licensed journeyman electrician for over ten years, but when a customer asked me to install an outside 30-amp outlet for his RV in the driveway, I accidentally wired it up for 240 volts, NOT 120 volts. That was a costly mistake on my part since it destroyed a lot of the RV appliances and electrical system. Yes, I paid for the RV repairs, but I hated to write that check. More folks need to understand that RV electricity does not follow the norm for house wiring. —Adam
Dear Adam,
I get emails like this every week from an electrician or homeowner who’s made this same costly miswiring mistake. An RV 30-amp plug is NOT wired for 240 volts like the home dryer plug it resembles. The first time I saw one of these TT-30 plugs on an RV I also assumed it was 240 volts, until I looked at the plug closely and saw it was listed for 120 volts. That was the hint I needed to avoid making an expensive mistake as well.
Dryer outlets
Below is what a 30-amp/120-volt RV outlet looks like compared to a 30-amp/240-volt dryer outlet. See why residential electricians can easily be confused because of the similar size and shape?
And here’s how 50 and 30-amp RV pedestal outlets are supposed to be wired.
Using welder outlets for your RV (Don’t do it!)
Note that a 240-volt NEMA 6-50 receptacle, which is the standard welding outlet many are proposing to use to power their RV, DOES NOT have a neutral conductor, only 2 hots and a ground. So if you want to hook it up to a 50-amp RV outlet there is no neutral conductor and no safe way to divide the 240 volts into 120 + 120 volts.
Remember, you can’t use the ground wire as a neutral as that’s a serious code violation and very dangerous because it’s not sized to carry full load current. So if the ground wire you’re using as a neutral were to open up (a real possibility) then that 240 volts could divide to 200 volts on the one leg and 40 volts on the other leg. And that will destroy half of your RV wiring (likely the expensive half).
Also, it would be disastrous to attempt to rewire this same welder outlet with a 30-amp RV outlet since the incoming power is 2-pole 240-volts, not 1-pole 120-volts. Doing so will destroy most of your RV’s electrical system in a few seconds. While it’s possible to rewire the circuit breaker in the panel to single-pole, and color code the existing wiring run, this is something you should have an electrician do since lethal voltages are involved.
So if you’re going to have a 30-amp RV outlet wired up for your RV when it’s parked at home, be sure to show this article to your electrician before he makes a costly mistake. Plus, it’s really a good idea for you to measure every new or unknown RV outlet for correct voltage BEFORE you plug in your expensive RV. Avoid that costly and time-consuming mistake.
And that’s also a great reason to purchase something like a Southwire Surge Guard 34931 for your RV. This is cheap insurance since it won’t let a 240-volt wiring mistake reach your RV’s electrical system.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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In your diagram showing the 30amp 110V RV receptacle on the left and the 30amp 240V dryer receptacle on the right, you have the “L” shaped connector labeled as “neutral”. I believe that should be labeled “ground” just like the welder outlet is labeled. A 30amp 240V receptacle wouldn’t have a neutral. I do understand that with modern dryers that tap off of one hot leg for 110V circuits do use the “ground” wire as a neutral. I believe that is why electric codes for new houses require a 4 wire receptacle for the dryer, so that there is an actual neutral and a separate ground.
Mike, is the Southwire 34931 the best option. I looked into products like this some time ago. Found a very wide range of products and features, with just as wide a range of cost. I am considering picking one up to use with my own “residential electrician” outlet here at home. Plus whenever I camp. I recall, some have the capability to lock it, (so nobody can steal your surge protector, etc.). I don’t mind paying the price for a good product. But it would be helpful to know what “extra features” are not really worth additional cost. That kind of thing.
Here’s a video I made a short while ago that explains what these EMS/Total-Electrical-Protection products do to protect you and your RV from too high, too low and hot-skin voltage. I really like the Southwire product you referred to the best since I think they have superior engineering, but Progressive and Hughes also make similar products that protect against over and under voltage as well as open-ground conditions. Watch me create failure conditions on my test bench: https://www.youtube.com/watch?v=z6P1MUDfWO0&t=0s
Thank you. Great information! I’ve shot a PDF of this article up to my cloud for future reference.
Oh, the stories I could tell. One of my projects is to produce a few articles and videos about this for residential electricians. I just need to find a way to distribute it.
RVT seems to bow to Facebook, must be something there…
While Facebook is a useful platform for reaching many RV owners, it’s not the preferred way to distribute important safety information to electricians and inspectors. That requires a more targeted media outlet of some sort.
Of course, it’s not unusual to have a small amount of voltage between neutral and ground. It’s when you exceed 1 volt (maybe 2) that you should investigate why. Just don’t want someone to freak out that they’re not getting zero volts when testing N-G levels.
Yes, but only on a loaded circuit. The key to understanding this mystery voltage is knowing that the neutral wire can have a voltage drop equal to the hot wire. So if you’re on a single-pole branch circuit and the voltage drops from 120 to 110 volts when you put a load on it, most likely only 5 volts of that drop is on the hot wire, and the other 5 volt drop is on the neutral. If you measure between the ground and neutral at the point you’ll see a 5-volt difference. That’s expected and nothing to be concerned about.
This happened to me when i had a licensed electrician wire my RV home outlet. I had specifically told him it was for an RV, and yet he wired it wrong. Fortunately I ALWAYS check an outlet before using it. He had to make a return trip to rewire and correct his mistake. Fortunately, no damage done.
Residential electricians often have no experience with RV electrical power, which is why they can make this mistake. But if you look carefully at an RV TT-30 outlet it’s stamped 125 volts max.