50 amp to a 30 and 20 out how to do? HELP!

CDP wrote:
I don't know what the code is for RV site services.

RVs and RV Parks are covered under article 551 of the NEC. Up until recently there was a free and easily accessible copy of the 2104 NEC online. Now it looks like you have to register with NFPA before you can get it for free. Maybe a free online copy of the NEC isn't currently available because of the new 2017 edition coming in?

There is a draft copy of the 2014 edition of the NEC here. I saw a draft of proposed changes for the 2017 edition recently and there was a proposal to require 40 percent of pedestals to be 50 amp but it looks like it stayed with 20 percent. Too bad because the NEC is waay behind on all the 50 amp RVs today. However, you won't find many new RV parks being built.

FWIW, a copy of the 2005 edition of NEC is here. Have not yet found the previous 2002 edition or others prior to that. The 2005 edition is when they increased 50 amp pedestals from 5 percent to 20 percent of the total in a CG.

I don't know what the code is for RV site services. A friend of mine ran into this fairly recently after a discussion on electrical services. Just out of curiosity, he checked the service he was plugged into at the time and discovered his two 25A circuits were on the same phase. He had voltage from hot to neutral on both circuits and "0" between the two. Of course you know this must mean they're in phase since any phase difference would show some voltage difference between the two. He didn't look into this any further before they left the next morning, and since it was of no consequence to him at the time anyway. He just thought it odd enough to comment to me during a recent conversation on the same subject.

I don't know how the pedestal in question was wired internally. Nor do I know if others in the same park were like this one. I made an estimate on how it might be wired to get the results of the same phase on both circuits of a 50A service.

Perhaps there have been changes in the code that might allow this, something the park manager did himself without knowing the code, or perhaps an honest error by someone else that should never have been working on a power pedestal. It is only 50A at 120V which really isn't that much for one conductor to the pedestal. I don't know. My friend is a retired Radar Engineer and I trust what he told me to be accurate. He's actually sort of anal that way. He probably took his oscilloscope to the pedestal for a better investigation. lol

CDP wrote:
Gil made some good points. But here is a newer point that may be rather rare yet.

You may not have 240V anyway. In some parks, you may run into a 50amp service that is two, 25amp, protected circuits of the same phase giving you "0" volts between the two.

I've never heard of that but wouldn't be surprised. If any park/CG is doing that, it wouldn't comply with the NEC which is quite specific on a what a 30 amp 120 volt and 50 amp 120/240 volt recept. is and what demand loads are for them. Some parks have general purpose handymen that also do electrical work and I'd worried there could be safety issues at stake as well.

Gil made some good points. But here is a newer point that may be rather rare yet.

You may not have 240V anyway. In some parks, you may run into a 50amp service that is two, 25amp, protected circuits of the same phase giving you "0" volts between the two. In residential services, the 240V comes from the voltage between two different phases. In commercial power distribution, the power companies change phase paring in residential areas to equalize load management. But every house has two different phases (AB, BC or CA). Within RV parks, it seems they're starting to do their own oddball phase load management since 240V isn't generally needed in RVs that I know of. I don't know about the small RV electric cloths dryers, I don't have one. But I suspect they run on only 120V.

The parks might just bring one phase to a slow blow, 50A breaker that's imbedded in the pedestal and feed the entire pedestal from that. If it's a dual pedestal, they may feed one side with one phase through an imbedded 50A breaker and the other with the other phase through another imbedded 50A breaker. They might feed one phase to odd number pedestals, or spaces, and the other phase to even pedestals.

If you check on the pedestal with a multimeter from one hot side to the other on the 50A receptacle and read "0" volts, you have the same phase. Then read from one side to the hot terminal on the 30A service and so on. If you read "0" volts between all hot sides, you have all of one phase. This assumes of course, the pedestal is hot as it should be. You can measure hot to neutral and/or ground first to make sure.

The benefit to the park of doing it this way is they can easily prevent guests from pulling any more than 50 amps no matter how a guest tries to get around it. The guests would not have access to the imbedded 50 amp breaker and would have to call park management to have it reset, if it isn't automatic. Since larger units today are becoming more and more power hungry, some folks trip a breaker when using the microwave on a hot summer night and try to get around that by "creative electrical engineering" and plugging one AC unit into the 30A or 20A service. They turn on the microwave and will still trip the imbedded 50A breaker.

I would expect to see more and more new parks wired this way. If guests are abiding by park rules, they should not have any problems except for the rare weak breaker. Breakers do wear out and get weak over time. But other than that, no worries mates.

That adapter looks fine.

First, be aware that even though the AC units may be high efficiency and draw only 1000 watts when running, that is at 120 volts. AC units draw more current as the voltage goes down and is opposite to resistive devices (heaters, coffee makers, etc.). When AC units start up, they have a momentary inrush current and for a high eff. AC is about 50 amps. If you read the manual for them, you will find that the min. wire is #12 ga. and breaker size is 20 amps. Running two AC units on the same supply would require a 40 amp breaker and if both started simultaneously, the inrush current would be 100 amps. Some find they can do it on 30 amps but they are risking damage to the AC units. If the voltage is much less than 120, a 30 amp breaker will trip. Don't forget there would also be additional load from converter, fridge, etc.

I would wire the new one on a separate 20 amp cord/circuit and plug it separately into the 20 amp receptacle on the pedestal using a 20 amp power inlet like Park Power. All pedestals always have a 20 amp (GFCI) receptacle by code (unless it's a really old CG) whether or not it has 30 or 50 amps or both. This would allow you to always plug into the 30 & 20 amp recepts. on a pedestal or to plug into a 50 amp one using that adapter with a 30 & 20 amp connector on it.

Note that CGs have a max. of 20 percent 50 amp recepts. by code. (NEC). As of the 2005 code edition, only 5 percent of CGs were required to have 50 amp recepts. in pedestals. Finding a 50 amp recept. can be extremely difficult unless you go to a high end RV park, some casinos or some gov't CGs.

If you do decide to always plug into the 20 amp recept., note that the pedestals and CG wiring are never designed to have both the 30 amp and 20 amp recepts on a pedestal running at the same time. Drawing close to 50 amps at 120 volts on a 30 amp only pedestal can cause excessive voltage drop which will eventually damage AC units. Never run the AC units below 105 volts. From a voltage drop perspective, plugging into a 50 amp recept. with an adapter would be better.

Having a permanently mount voltmeter inside is highly recommended to monitor the CG voltage. Even better, get an EMS unit that will automatically shut power off. Progressive Industries has the best one. There isn't one available for 20 amps tho.

Using an adapter introduces one more potential failure point in the shore power connection due to overheating from a bad connection. Never plug in live - shut off pedestal breaker(s) first. Failing to do this will lead to pitted and dirty plug blades and inside a recept. cause overheating and resistance. Always make sure your plug blades are kept clean.

For use on a 50 amp site that is a good choice less you want to fully upgrade the RV.. I like your plan by the way.

The other option is to upgrade to 50 amps, new power center (if you do not have generator with a transfer switch all you need is a new center and a new cord)

But bring that 2nd A/c out to a "Break out" spot (Plug and outlet) so you can "Split" it off when on a 30 amp site

But if you are currently comfortable with 30 amp service, that is Overkill.

One suggestion: Carry a 12ga extension cord, Sears or K-mark cords with the push button on the outlet are my favorite, but any good 12ga cord will do, say 25 Feet is likely long enough (my Sears cord is 100' but I only use it .. rearley, I have a 10 and 20 foot for routine use) On a 30 amp site you use that cord to the park's 20 amp outlet

On a 50 amp site use your splitter

I think you will be very happy.

One final caution:
People will talk about the "Danger" of plugging a 30 amp cord into a 50 amp breakier,... yes there is danger. very slight.. The 30 amp breaker inside the RV (and the 20 amp on the 2nd A/C) will provide protection against nearly all problems. A short in the shore cord will trip the 50 before anything bad happens, and a short "Downline" the breakers inside the RV

Iun fact, if you accidently try to draw 35 amps the big difference is you won't have to go out in the driving rain to reset the park breaker.. you will like that.

At the end of the day what you have with 50 amp RV service or conventional 240V service is two legs of 120V each, a neutral, and a ground. How you break that out to different connections is determined by what fits your needs.

You don't mention about any power inlets you have but the assumed 30 amp RV power inlet of either an attached cord or an exterior plate mount inlet. If you establish either a cord or plate inlet for the new 120V A/C service, you will want to split the 240V service and connect appropriate connection to that service. Sometimes, this is most elegantly done by building a breakout box that has either a 30 amp outlet and 15 amp outlet (two receptacles) or passing through one leg of the 50 amp service and having a single 15 amp receptacle.

An alternative to a break out of the 240V service is to connect with the traditional 30 amp cord and have an additional 120V cord to the pedestal as most campground pedestals have both.