I’m new to a 50-amp rig. I have a 30-amp plug in my garage that’s set up for my old pull-behind camper at 120v. I also have a 50-amp plug that is 220. Is this the proper plug for my 50-amp motorhome? My local RV guy says no, but the seller says it’s what is required with the proper 50-amp receptacle. Don’t know who to believe and I certainly don’t want to fry anything. Who is right? —Travis, 2004 Winnebago Adventurer 35U
Your RV guy is correct, and this can be a dangerous situation when someone wires a 50- amp plug for a welder or 220-volt power. It can even happen on a 30-amp plug that is wired to a dryer, as it is also 220 volts.
30-amp RV plug
On the 30-amp outlet, you have one hot leg that brings 120 volts and a ground and neutral. If you test this with a multi-meter it will read 120 volts between the hot and ground, 120 volts between the hot and neutral, and 0 between the ground and neutral. In a 3-prong residential dryer outlet, there is a Hot 1, Hot 2 and neutral, so it has 240 volts and can cause damage. Make sure whoever is installing the outlet, or if there is an existing one, knows that it should have these voltages. The dryer outlet would have an L-shaped neutral at the top while the RV 120-volt has a semi-round ground at the top and the neutral is a slot. However, someone can purchase the correct outlet but wire it wrong!
50-amp RV plug
A 50-amp RV outlet has a Hot 1 and Hot 2 that are both 120 volts/50 amps, plus a neutral and ground.
This is a little deceiving, as Hot 1 goes to one side of the distribution center and Hot 2 provides power to the other side, so it is never 240 volts but rather 120 volts/50 amps to each side. In this situation, you should find 120 volts between ground and Hot 1, Ground and Hot 2, Hot 1 and neutral, and Hot 2 and neutral. You should find 240 volts between Hot 1 and Hot 2 and nothing between ground and neutral.
You can have the 220-volt welding outlet rewired correctly. However, if the 30-amp worked for your travel trailer, it will be fine for your Winnebago with a 50-30 reducer. You just won’t have full power and need to conduct some energy management. You will not be able to run both roof air conditioners at the same time unless you have SoftStartRV. I would suggest a Southwire Surge Guard that will tell you the amp draw, voltage, and if it is wired correctly.
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