I recently acquired a setup which has a 30-amp plug on one side and a 20-amp plug on the other. I was told that if you plug in one side to a 30-amp source and the other to a 20-amp source, you will end up with 50-amps. Is that right? There’s no brand name on it, so I assume they are homemade. — Jerry M.
Thanks for your question. This is one of those confusing things that sort of works, but is not exactly to code. Basically this “cheater plug” is designed to obtain as much power as possible from a pedestal that doesn’t have a 50 amp receptacle. That’s so you can plug in your 50-amp RV shore power and operate all the appliances. That’s right, it’s supposed to grab power from both the 20-amp and 30-amp outlets on the pedestal, and feed it into your 50-amp shore power plug.
So, does it work and is it safe? Well first, lets review how much power is available in a typical campground pedestal. If you use a standard 30-amp to 50-amp adapter plug (like on the left) to plug in your 50-amp shore power line, you’ll be limited to 30 amps total, which will be split between both sides of your RV’s 100-ampere electrical system. Yes, that’s right! Even though we call it a 50-amp plug, it’s actually 50 amperes times 2, for a total of 100 amperes. That’s why it’s so easy to trip a 30-amp breaker on a pedestal using a 30-to-50 amp dog-bone adapter. Your RV really wants 100 amperes of current to operate everything at once.
Now does the cheater plug at the top give you more power? Well, it could except for the fact that most 20-amp pedestals are GFCI based, and the unbalanced current caused by the two neutral sides being tied together will likely cause it to trip immediately. But if you do plug it into a non-GFCI 20-amp receptacle it should work. It will provide 30 amperes of current to one side of your RV’s circuit panel, and 20 amperes to the other side. That adds up to 50 amps total, which still might not be enough power to run everything you want at the same time. However, be aware that a lot of 20/30 amp pedestals can only supply a total of 30 amperes of current. They expect you to plug into the 20-amp outlet OR the 30-amp outlet, NOT both at once.
And is it safe? If we just consider amperage draw, it should be. Even if both the 20 and 30 amp outlets are on the same power leg (which is likely), there’s only a maximum of 50 amps of return current possible on the neutral. And the neutral wire on a 50-amp RV plug is designed for that much current. However, if you use something like a cheap-heat system in your RV connected across both legs of the shore power for 240-volts, it’s possible to back-feed 120-volts across the cheater plug. And that indeed could be dangerous if one of the plugs is pulled out of the outlet.
I just don’t think cheater plugs like this are worth the risk since you might not be able to control exactly what’s plugged into them. It’s really better to find a 50-amp pedestal and be completely safe.
Let’s play safe out there…