RV Electrical

Battle of the dog bones

Are all RV power adapters created equal?   This post is about two “dogbone” adapters —  one of which I sent back! 

 

 

Anyone familiar with RV electrical systems knows that the shore power provided by the park doesn’t always match the coach.  Our 35′ fifth wheel (an Alliance Paradigm 310RL) is designed for 50A service but my wife and I like to frequent National and State Parks where the shore power is often only 30A.  Some are even 15A, but that’s a subject for another day. 

Enter, the RV “dog bone”  

Both of the devices devices shown in the photo will allow a 50A RV to plug into 30A shore power. How do they do that?   To answer that question,  I’ll first outline the electrical system of a 50A coach and how that differs from 30A shore power.  I’ll then show how these dog bone adapters are wired —  It will feel a bit “geeky” at first but you’ll see right away how it all works. 

The 50A RV

Modern 50A RV electrical service consists of TWO 50A  (120V)  legs (for example, a coach with two air conditioners will wire one of them to “leg 1” and the other to “leg 2” at the service panel). Such a service requires FOUR wires at the pedestal:   Two  “hot” legs, each with 50A capacity, a neutral and a ground.    That’s right:  True, 50A service is really 100A total capacity.

30A shore power

30A shore power at the park consists of ONE 30A (120V) leg and requires THREE wires at the pedestal:  One  “hot” wire with 30A capacity,  a neutral and a ground.

How can we connect a four-wire 50A shore power cord from the coach to a three-wire 30A supply?   In a nutshell, the dog bone binds “leg 1” and “leg 2” together on the 50A side, and connects this to the single 30A leg at the pedestal.  That means a single, 30A supply is available to the entire coach, so that you don’t have to worry about “leg 1” vs “leg 2” (you do, of course, have to limit your electricity consumption to avoid tripping the breaker at the pedestal).  Below find a diagram showing how this is accomplished. 

 

In this photo, the “30A Male” end of the dog bone plugs into the 30A pedestal, and the 50A female end of the dog bone provides the “50A” connection for the coach’s shore power cord.  This is the correct way to power a 50A coach from 30A shore power.  

 

 

Now then, what about the two dog bones I am holding in the first photo?  I verified that  both are wired correctly (L1 is tied to L2 as in the diagram), but only the yellow one (a Camco #55185)  possesses the “ETL listed” seal and proof of compliance with Canadian Electrical Code CSA STD.C22.2 No. 21.  The ETL listing means something — it means this dog bone has been independently verified (by Intertek) to meet the Canadian standard.  That’s important.  

The green dog bone (RVGUARD “30Amp to 50 Amp RV Adapter Cord”), possesses no such certification, and the manufacturer did not respond to my request for clarification.  As I mentioned before, the RVGUARD is wired correctly and no doubt will work, but it has not been independently verified to meet any recognized standard.  I sent it back.  

Winner:  Camco #55185

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