I just taught my first RVelectricity seminar in 16 months at the Airstream International Rally in Lebanon, TN. The question of whether an RV uses 120 or 240 volts kept coming up over and over again. I was in the parking lot showing off my Ford F-150 PowerBoost Hybrid truck with the built-in 7,200-watt generator.
Expect a full report after my two weeks of playing with the cool loaner truck. But right now I’m just focusing on how the generator works.
Questions about 240 volts…
There were several well-meaning attendees standing around as I was getting ready to plug in a 50-amp Airstream shore power cord to the 120/240-volt outlet in the bed of the F-150 PowerBoost. They kept warning me that I was going to blow up this expensive Airstream trailer if I plugged it into the twist-lock outlet in the truck. One went so far as to tell them I needed to ask that No~Shock~Zone guy how to do it(!).
Hey, that’s me!
Yes, I am that No~Shock~Zone guy, and I do know how split-phase power works in an RV. The concept is pretty simple, just like in your home where there’s a 240-volt electrical service that’s connected to one phase of the power company feeder.
And just like in your home, this 240-volt transformer is split in the middle with a neutral conductor, which provides 120 volts on each of the hot legs. So if you connect an appliance to the neutral and either of the hot legs you get 120 volts. But if you connect anything between Hot 1 and Hot 2, that voltage adds together and you get 240 volts.
What’s in an RV?
Note that in 99% of the RV builds, even though 240 volts is coming into your power center on Hot 1 and Hot 2, your circuit breakers are wired so that only one of the split phases connects to any appliance. Generally, the manufacturer wires the panel to help balance the amperage loads between Hot 1 and Hot 2, simply so you can get the maximum power the pedestal can provide.
Remember, this is connected to a 2-pole circuit breaker with a common trip. So if one leg goes over 50 amps current, it will trip both legs at the same time, even if the other leg only had a few amperes of load.
How did I connect the F-150 PowerBoost?
In this case, the F-150 has an L14-30R twist-lock outlet that’s wired exactly like a Honda EU7000is generator, which I’ve used many times. So by plugging in a 4-pin twist-lock to a NEMA 14-50R adapter, I created a 50-amp-type outlet just like a pedestal, even though it only had 30 amps of current available from each leg instead of 50 amps. So it could provide up to 60 amps of combined current at 120 volts. That adds up to 7,200 watts (the generator’s maximum outlet), instead of the 12,000 watts that a fully powered 50-amp outlet can provide. But that’s still a significant amount of power for most RVs.
Split-phase confusion and 30-amp outlets
Don’t feel bad if this seems counterintuitive, because I get this type of question from electricians all the time. However, be aware that this is NOT what you want to do when wiring a TT-30-amp RV outlet for your house.
If your electrician makes a mistake and wires it up a new 30-amp RV outlet with 2-pole 240-volts (like a dryer outlet) instead of 1-pole 120-volts, then you’ll fry your RV’s electrical system in a heartbeat. So please don’t let that happen. Always measure ANY new 30-amp outlet to be sure if was properly wired with 120 volts.
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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