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Author Topic: 30 amp service for 50 amp bus  (Read 3969 times)
busenthusiast
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« on: August 29, 2011, 10:57:56 AM »

Just got back from a wonderful week at Hunting Island State Park just outside of Beaufort, SC. This was our third trip out with our bus and everything worked pretty much perfect. The only bump in the road was when we decided to take advantage of a beach front site that came available. The site we were on was a 50 amp site and the one we moved to was a 30 amp site. No problem, I had my trusty 30 amp male to 50 amp female dogbone. Now, I'm not the sharpest knife in the drawer but I do learn real quick. I moved and rewired the previously installed, code violating, breaker panel and adjusted the loads so everything was balanced. It never dawned on me though that if the chance came to pass that if all I had was 30 amp service, then I'd only had one leg of my normally available two legs of 120 volts. Of course, when I plugged my adapter in and went to turn on the AC in the front of the bus......no power. Had me scratching my head at first (remember.... cue the somewhat dull knife) until I realized that in the back of my mind I always knew that 30 amp RV service only provides one leg of 120 volts. After removing my breaker panel cover and inspecting with my digital VOM, as luck would have it my front AC and most of my other important electrical needs were on the other leg of the 50 service (the one not seeing power from the dogbone adapter)......so I killed all the power and swapped the two legs at the CAMCO plug I have installed and bada bing, back in service......well half service anyway. Well the next logical question (at least logical to me) came to mind. What do most RVer's do when in this situation? Are normal 50 amp RV services wired in such a way that if you are faced with only 30 amp service as an option then at least you have your most needed electrical supplies delivered? Or is there an adapter that piggybacks the two 120 volt legs of the bus' 50 amp service together so that you can pick and choose what you want to have power for?
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Len Silva
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« Reply #1 on: August 29, 2011, 11:05:55 AM »

The typical 30 amp male to 50 Amp female adapter has the two legs strapped together in the adapter.  Is this one you purchased or made up yourself?  Easy fix.

You will have both legs available but will have to do some load management.
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bevans6
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« Reply #2 on: August 29, 2011, 11:30:15 AM »

Just don't use that type of bridging dog-bone adaptor if you have any 220 volt loads than need to bridge across both legs of a 50 amp service.  I'm not sure that anything catastrophic would happen, but at the least the 220 volt appliance won't work.

Brian
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« Reply #3 on: August 29, 2011, 11:41:15 AM »

That's right, nothing would happen except that the 220 volt appliances wouldn't work.  They are not going to work anyway.

It's the same basic setup if you have a 240/50 amp shore connection but your generator is wired for 120 volts.  In that case, the generator is strapped to both sides of the panel.
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busenthusiast
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« Reply #4 on: August 29, 2011, 12:19:29 PM »

Well obviously I didn't search hard enough because I couldn't find any indication of a dogbone that connected the two legs. I purchased this one from AdventureRV.net. Looks like I'll need to purchase another one now......thanks for clearing that up guys.
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MEverard
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« Reply #5 on: August 29, 2011, 04:14:50 PM »

I thought all adapters had the two legs tied together. If they weren't, the adapter would not serve the purpose it was intended for.

Mike
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Mike Everard
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« Reply #6 on: August 29, 2011, 04:37:07 PM »

I just double checked mine again a couple of hours ago.....I must've got a dud.
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busenthusiast
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« Reply #7 on: August 29, 2011, 05:53:28 PM »

As a follow up, this is the adapter I purchased. After reading the description a little more closely, I think I may have got just what I bought. I've got a trouble ticket submitted to the website to make sure.
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neverlearn
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« Reply #8 on: August 29, 2011, 06:26:55 PM »

I realize that this doesn't answer your question - however another member previously posted a real good reason why you may want to think twice before using a 30 amp to 50 amp adapter:  Your 50 Amp draw will overload the neutral of the 30 Amp service.   Some parks will have a sample of a melted 30-Amp receptacle as an example of some of the damage which can be caused by using the adapter.
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« Reply #9 on: August 29, 2011, 07:18:11 PM »

I realize that this doesn't answer your question - however another member previously posted a real good reason why you may want to think twice before using a 30 amp to 50 amp adapter:  Your 50 Amp draw will overload the neutral of the 30 Amp service.   Some parks will have a sample of a melted 30-Amp receptacle as an example of some of the damage which can be caused by using the adapter.

Huh?  How does that work?  The adapter simply converts a 30 outlet for use with a 50 amp plug.  One can't pull more than 30 amps or the breaker will blow.
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Sean
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« Reply #10 on: August 29, 2011, 07:31:26 PM »

I just double checked mine again a couple of hours ago.....I must've got a dud.

Yes, you got a bad one.  I would return it for credit, if you still can.

As a follow up, this is the adapter I purchased. After reading the description a little more closely, I think I may have got just what I bought. I've got a trouble ticket submitted to the website to make sure.

I don't think so.  I think whoever wrote that bit of copy was not an electrical genius by any stretch.  For example this:
Quote
If RV is wired normally it prevents the use of the 20 amp side of RV panel.

Is either meaningless, or just plain wrong.  A "normally" wired 50-amp rig does not have a "20 amp side" of a panel.  It has two 50-amp sides.  I am guessing they meant that it prevents use of 240-volt loads, but who knows.  Whatever they meant, it makes no sense as written.

I would not let them use this to weasel out of refunding your money or replacing the cord.  Moreover, this:
Quote
They are Heavy-duty 10/3 ST power cords with 3-wires plus ground.

is also just plain wrong.  This type of adapter uses 10/3 cord, which is three wires including ground, not "plus ground" (which would actually make it 10/4, good buddy).

BTW, I just replaced my 30-to-50 dogbone, which gave up the ghost after over 20 years of service  (http://ourodyssey.blogspot.com/2011/07/relaxing-on-clinch.html).  A perfectly good 10/3 model cost me only $15 at Camping World, so perhaps the $5 saved by buying from this outfit is a false economy.

...  Your 50 Amp draw will overload the neutral of the 30 Amp service.   Some parks will have a sample of a melted 30-Amp receptacle as an example of some of the damage which can be caused by using the adapter.

This is also not correct.  On a 30-to-50 dogbone there is no way to "overload the neutral" without first overloading the hot, which should trip the breaker.

Perhaps you are thinking of the "two-fer" adapters that allow you to connect your 50-amp rig to two 30-amp receptacles.  This is a box with a 50-amp outlet in it and two short cords with 30-amp plugs.

These boxes, in untrained hands, are dangerous for several reasons.  One of those reasons happens to be that connecting the two 30-amp plugs to receptacles that are on the same leg of power, rather than opposite legs, can, indeed, overload the neutral, putting a full 60 amps on it.  That said, 60 amps on a cord rated for 50 is unlikely to melt it, and you'd have to try really hard to get 60 amps onto it in the first place.

Campgrounds have a very different reason for discouraging the use of these "two-fers", namely that they don't want you using twice as much power as you've paid for.  So it would be no surprise that they would resort to scare tactics like melted adapters at the front desk.  FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
« Last Edit: August 29, 2011, 07:43:17 PM by Sean » Logged

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« Reply #11 on: August 29, 2011, 07:48:47 PM »

Well written "fact" post Sean.  it helped me understand or confirm a few things.  thanks.
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« Reply #12 on: August 30, 2011, 05:49:18 AM »

I'm always amazed after reading posts like these that there aren't more "accidents", in spite of Sean's best efforts and well documented best practices. I wish folks would study these materials first before tackling some of these tasks, and especially before offering "suggestions".
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scanzel
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« Reply #13 on: August 30, 2011, 10:03:02 AM »

I think Sean should write a good book on the subject which would help the rest of use out on electrical wiring etc. Some wiring diagrams would be great also. Or maybe even charge for his services. I would be willing to pay after I provide him info on what I have and what the best way to do it is.
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Steve Canzellarini
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niles500
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« Reply #14 on: August 30, 2011, 09:30:23 PM »

"I think Sean should write a good book on the subject"

If some one would compile it - I think he pretty much has - FWIW
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