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Ask Dave: Why does only one side of the circuit breaker work with 50-15 amp dogbone?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses dogbone adapters and circuit breakers.

Dear Dave,
I have the 50-amp to 15-amp adapter which my dealer sold me. I run a good-sized 100′ extension cord from the adapter to my regular garage outlet (standard 110v outlet) that is on a 20-amp circuit. With this configuration, only half of my distribution panel works in the RV. That half has no outlets in the RV energized on it (including the refrigerator, microwave, TV) and the two batteries for the 5th wheel will NOT charge (but the A/C over the bed will work and the washer-dryer plug).

I use the 50-amp shore cord provided by Mesa Ridge (Jayco) with an adapter to a 30-amp cord, and another adapter from the 30-amp cord to a 15-amp male. I plug the same extension cord into the 15-amp adapter, then into the same outlet in my garage. Like presto magic, everything is energized in the RV including the refrigerator, TV, Micro and the batteries will now charge!!

My electrician was puzzled by this.

He said the only remedy would be to swap the two main electric wires coming into the distribution panel, so the half with the outlets (refrigerator, batteries, etc.) will work. I called my dealer and checked on the Mesa Ridge/Highland Ridge owners forum and everyone said the same thing; the 50-amp adapter to 15-amp should energize both sides.

I am really confused. I have tried two different brand 50-amp to 15-amp adapters, different extension cords and other outlets all with the same result. Also, I replaced the GFCI in the RV thinking that was the problem.

This is my first 5th wheel and my first 50 amp. My travel trailer had a 30 amp. I used an adapter straight off the trailer with no problem. My trailer is out in front of my house. —Gena

Dear Gena,
(Gena and I have talked several times since this first question came my way and we were able to get a little more information, as this was something new to me, as well.)

First, the 50-amp power cord has two “hot” wires that supply 120-volt power to each breaker in the distribution center.

The power bar on the typical distribution center has two main breakers in the center that supply power to both sides. Here is a wiring diagram from a Progressive Dynamics 4500 model.

Two-poled circuit breaker

Notice the “AC In Hot 1” and “AC In Hot 2” in the red square with the wire from each going to the representing circuit breaker circled in red. These circuit breakers are two-poled, which means there is a bar going across the tabs so if one side trips, they both trip.

However, when using a “dogbone” that reduces from 50 amp to 15 amp, like you suggested, it eliminates one hot side and only provides one to the “AC In Hot 1” side—therefore your issue with only half the panel working.

Note: I would never suggest using this type of extension cord without verifying it is at least 15 amps or more!

Distribution center has two breakers

I verified with Dennis from Progressive Dynamics that their 50-amp distribution center has the two breakers, and if you are using the typical “dogbone” reducer/adapter it will only power one side.

So, why does the 50-30-15 configuration work? After doing research and getting a close up photo of what Gena was using, we can see the 50-30 amp reducer has a “jumper” wire that provides power to both L1 and L2 of the 50-amp plug going to the coach!

This configuration will work; however, it requires leaving two expensive cords out in the open, the 50 amp and the 15 amp, plus creates a cord length that is dangerously long. It is best not to go past 50 feet if possible and use the correct gauge wire/cord. A 50-amp cord is 6 gauge, 30-amp is 10.

Note: Much better 15-amp extension cord!

After more research and talking first with Jim at Northern Wholesale Supply, who referred me to Brad at Park Power, he suggested the model 1550 ARV, which plugs into the side of the rig. Your 15-amp extension cord can go straight to that.

According to Brad, this adapter will split the power to both wires on the 50-amp plug and therefore supply power to both circuit breakers. Keep in mind it will only provide 15 amps total, so you are very limited to what can be run. Do not run the roof air conditioners as they can draw up to 14 amps each. The refrigerator will draw 8-9 amps and will also draw 12-volt power from the house batteries which in turn will kick in the converter or inverter/charger that will draw another 8-9 amps. I would suggest getting a Kill A Watt® meter and plugging it into your outlet, then plug in the extension cord to see what you are actually drawing.

Also, make sure the outlet you are plugging into is not “ganged” with any other outlet and the cord is not too long so as to create a power drop. In my opinion, it is best to install a dedicated 30-amp circuit for your rig if possible.

Read more from Dave here

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ZapEm
4 months ago

This was an easy one to solve. If only half the panel is supplied then half is getting power from shore. I know many models are different but that is the primary clue. The secondary clue was the intermediate cord powering it fully, there must have been a jumper inside as I’ve built one myself for this express purpose when using low current applications but want to power both sides. However, the best solution is a dedicated shore receptacle with dedicated cord. It sounds like her panel is 240V hence the whole issue but I would verify that one as many an RV have been fried by that mistake. In her case, since she hasn’t a clue she would need an electrician, a different one by the sounds of it since her original person was clueless… which makes me wonder why they are an electrician.

Bob M
4 months ago

The bad thing about the Parkpower adapter is it can’t be used in wet locations. So if you wanted to leave it hooked up at your RV you can’t incase it would rain. Unless you use elect tape to seal the connections. The other thing is it is only rated for 15 amps. Some people like me also have a 20 amp outside receptacle which would mean you should be careful on what your running inside your RV. My house only has a 100 amp panel so many of us can’t hook up a 50 amp outlet. I use the dogbone adapter only for when I need to run the fridge or putting my slide out and charging the batteries.

ZapEm
4 months ago
Reply to  Bob M

100A is plenty, you can easily install a 50A receptacle but keep in mind you’re limiting your current to the cord from shore to RV… that will be your limiting factor. But multiple loads inside your house and RV might barely touch 50A altogether (runs together, dishwasher, dryer, AC all at the same time… maybe. Seriously, add them up and realize you probably won’t come close to 50 let alone 100.

Irv
4 months ago

Installing a dedicated 30amp or 50amp circuit would be much better and not that expensive. (If you have an RV with 50 amp service, you can afford it.)

David Solberg
4 months ago

Bob is correct, and my original comment should have stated it provides 120-volt power to each breaker and not referred to the amps. I have corrected it. Mike is truly the electrical expert I was merely trying to help figure out why one side works in a certain situation and not the other. Thanks for the comment.

Bob
4 months ago

“First, the 50-amp power cord has two “hot” wires that supply 30 amps of power to the distribution center.”
This is not correct. The 50 amp cord has two 120 circuits and each circuit supplies 50 amps, for a total of 100 amps, 12,000 watts
This is the reason the 50 amp plug uses 6 gauge wire. 2-6 gauge, 120 volt, 1 6 gauge neutral and an 8 gauge ground.
Quote from Mike Sokol, April 2019:
“That’s the most relevant question, and the answer is 12,000 watts. Here’s why. While it seems confusing to think about a 50-amp outlet as having 100 amperes of total current available at 120 volts, that’s actually correct. That’s because there’s a 2-pole circuit breaker in the pedestal (at least, there should be), and each pole is rated for a maximum current of 50 amperes before it trips. So you can pull up to 50 amps from one pole, and another 50 amps from the other pole.”

ZapEm
4 months ago
Reply to  Bob

Bob, that isn’t quite correct.

A 50A receptacle should be thought of as having a 50A maximum. Yes, when using any hot leg to neutral, you get 120v, the primary use is usually hot to hot (L1 to L2 for ease of use) that will be 50A maximum. Theoretically, using L1 to neutral is 50A and L2 to neutral is 50A and if you balance your loads the power coming back on the neutrals should mostly cancel out.

In essence, it can be used as 2 separate branches but in practice one should operate it as a 50A max for safe practices. You’re not wrong but not fully right either. It will trip at above 50A using 240v… which is a lot of power anyways, 12,000 watts no matter which way you slice that bread. If you’re using 12kW then you must be throwing a concert with massive speakers lol

Alan L Utzig
4 months ago
Reply to  ZapEm

Almost every RV uses the 50A power as two 120 volt circuits, not 240 volts. Therefore you are able to use 50A on each leg at the same time. The only exception is if the RV has a clothes dryer that uses 240, but I have never seen or heard of that situation in an RV.

Dr4Film
4 months ago

The short answer is that the 50 amp to 15-amp Dog-bone the dealer sold the customer is defective and built wrong. Whoever made the adapter didn’t have a clue. There are adapters available on Amazon which are wired correctly to power both sides of the RV. Of course, you have to be careful not to draw more than what is available at your shore power supply unless you have an Intellitec EMS power management system installed which will manage the incoming power for you.