By Mike Sokol
As many of you know by now, I just started an RV Electricity Group on Facebook a few days ago, and already have more than 800 members (you can join it HERE). So I’m getting lots of interesting questions that I can answer more at length in my weekly articles. I recently wrote a post about the line of Tesla charging stations I saw in Live Oak, FL, on my way back from the RVillage Rally 2.0, and received some interesting questions about what kind of dogbone adapter would be needed to connect your RV to a Tesla charging station.
After all, the theory goes, since Tesla supplied a special charging cable for their electric cars that would plug into an RV 50-amp campground pedestal, shouldn’t the reverse work? Does anyone sell a dogbone adapter that will go from the NEMA 6-50 outlet feeding powering electric car charger to the NEMA 14-50 shore power connector on an RV?
The answer is while that sort of adapter cable does indeed exist on eBay, NO you DO NOT want to connect your RV to any 240-volt outlet feeding a Tesla charger (or any other 50-amp/240-volt electric car charger for that matter). Doing so can risk extensive damage to your RV as well as the charging station circuit.
Here’s why: As you all should know by now, the 50-amp shore power connection for an RV is a 4-wire circuit, consisting of 2 hots, 1 neutral and 1 ground wire. And while it does indeed measure 240 volts between the 2 hot lines, the neutral wire is what allows you to derive a pair of 120-volt circuits. That’s because virtually everything in an RV (except for some of the largest coaches) uses 120 volts. The neutral wire is the only thing equally dividing the incoming 240 volts into 120/120 volts for the two 50-amp circuits. Lose the neutral and the 240 volts feeding the pedestal no longer divides into equal 120-volt legs. It can go as crazy as 200 volts on one leg with 40 volts on the other leg. Not good for your electronics!
Because electric cars use only 240 volts for their chargers, the manufacturers don’t have to bother running a neutral wire and generally use something like a NEMA 6-50 outlet for power. This is how most fast electric car chargers work (until you get into the 480-volt/3-phase supercharger versions). That saves money and space, and is perfectly safe for 240-volt-only circuits.
However, you can indeed buy an adapter cable that will allow you to plug your RV’s 50-amp shore power connector (a NEMA 14-50) into what’s basically a welding outlet (a NEMA 6-50) that’s been installed to power a fast-charging station. And while this may seem to work properly at low amperage, if you pull appreciable 120-volt current the smaller gauge ground wire in the branch circuit can be overloaded, opening up your RV’s neutral conductor with bad consequences.
What’s happening is the neutral current (which can reach up to a full 50 amperes) is improperly returning into the ground wire (officially called the EGC or Equipment Grounding Conductor). That can actually overheat and damage the ground connections for not only that outlet, but other outlets in the area as well. If that ground wire (that your RV is treating as a neutral) opens up or otherwise loses connection, then the split-phase divider no longer works, as I mentioned above.
And that’s why using the ground wire in a NEMA 6-40 receptacle for split-phase neutral currents is a code violation. The EGC ground is only there to create a fault-current path to the service panel’s Neutral/Ground bonding point in the event of a short circuit somewhere, not be a replacement for the neutral conductor.
So YES, you can plug your Tesla into a campground pedestal’s 50-amp outlet. But NO, you can’t plug your RV into a a NEMA 6-50 receptacle powering a Tesla (or any other manufacturer’s) fast charging station. It’s a code violation and dangerous to try. So just don’t do it!
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40+ 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.