This is simpler than you might think, but an adapter doesn’t make extra power…
Dear Mike,
On one of your webcasts there was a question about the two legs of 50-amp service. What does each leg power? Are they independent circuits? Just wondering because I seem to be able to run anything if hooked to 30 amp – but not at the same time without tripping a breaker. Thanks. —Steve Peterson
Dear Steve,
Great question. Yes, there are two independent hot legs on a campground pedestal with 50 amperes of current each, which powers two different sections of your RV’s breaker panel. The RV builder should have balanced the current loads so that one of your air conditioners is on Leg 1 and the other air conditioner is connected to Leg 2. They’ll also do something like put the microwave on Leg 1, and the bathroom outlets on Leg 2, and so on.
While the industry calls this a 50-amp/240-volt RV outlet, it actually has two independent 120-volt legs, each of which is capable of supplying 50 amps of current. So there’s 100 amperes of current available (50 + 50 = 100), with a maximum of 50 amperes from each leg. That’s why the currents needs to be balanced. If you exceed 50 amperes of draw on either leg, both poles of the circuit breaker will trip and ALL the power will go out.
Power to both legs…
To answer the second part of your question, a 30-amp dogbone adapter feeds a single 30-amp/120-volt leg from the pedestal outlet into both power legs of your RV’s shore power cordset using a jumper wire inside of the 50-amp outlet. That why a single-pole 30-amp outlet with a dogbone adapter can power everything in your 50-amp shore power RV.
However, this also means you only have a total of 30 amperes of 120-volt current available to power everything in your RV, instead of the 100 amperes total you have from the two 50-amp/120-volt legs in a 50-amp outlet. So you can’t run your hair dryer and air conditioner at the same time or you’ll trip the 30-amp circuit breaker in the pedestal or your RV load center This isn’t really dangerous if it happens – just possibly inconvenient.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there… Mike
Our trailer is a 30 amp unit, but we carry a 50 amp to 30 amp converter plug for those times when the 30 amp pedestal plug looks well-worn and questionable. Works fine, but is this as ‘alright’ as I think it is?
I would think you would be fine as long as your 30 A breaker in you RVs load center is working properly. Both pedestal breakers are 50 A and you would be connected to one of them depending on which leg you are plugged into. My understanding is that breakers are sized to protect the wiring in any electrical system. This then begs the question of wire size. For example, I believe my trailer is wired with # 10 wire which is rated for 30 A. I would assume your RV is as well. So, is there any issue with connecting a 30 A rated shore power cable to the 50 A to 30 A adapter which is protected with a 50 A breaker at the pedestal? I would assume that UL or some AHJ has blessed this connection scheme but best if Mike comments on this as I am not an expert.
My trailer has a 30 Amp system but stating the obvious, a 50 Amp system must have double 50 Amp breakers (as Mike mentioned). When using a 30 A to 50 A adapter once the current draw in either leg exceeded 30 A, the 30 A pedestal breaker would trip. So, it would seem that you’d never trip either of the 50 A breakers in the RVs load center.
Doug, you are 100% correct. If you’re powering from a 30-amp pedestal outlet, the 30-amp breaker in the pedestal should trip firstt. And it’s unlikely you would ever trip the 50-amp double-pole breaker in your RV’s load center.