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Old 06-21-2021, 02:24 AM   #1
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20 amp, 30 amp, and running both AC units

Few questions about the electrical system.i have a 1993 Gulf Stream Scenic Cruiser. It has a plug for 30 amps and what must be a 20 amp connection to plug into the grid. I have a good understanding of electricity and the limitations with current and wire gauges. I have seen splitters which turn a 240V 50 amp plug into two 120V 30 amp plugs. What would I accomplish by plugging this "splitter" into a 50.amp outlet, and then plugging my 30 amp plug from the motorhome into one part of the splitter, and then the 20 amp plug from the motorhome into the other part of the splitter? I'm assuming that, while this equates to two separate power cords with 30 and 20 amp limits, the motorhome itself would not care as the unit has one electrical system. It doesn't have two separate circuits for each or the plugs, and thus it will be limited to 30 amps at 120v. Is my assumption correct?

Or the better question is, can I use both my 30 amp and 20 amp RV plugs and plug each of them into separate circuits to my house (with separate circuit breakers) and get a bit of extra current? Again I'm guessing not, since there is only one circuit in the motorhome itself.

The other part is running both ACs. I plugged my 30 amp outlet into a 20 amp receptacle using an adapter today. So the motorhome should "think" it's 30 amps. I could only run one AC unit at a time. Turning one on would turn the other off. Was the RV smart enough to know it was using a 15~20 amp circuit? I can't see why it would know that. Or is my unit limited to using one AC at a time (that wouldn't make sense either, why have two units if you can only use one at a time)? Maybe I can only use two while the generator is on?
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Old 06-21-2021, 06:05 AM   #2
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The 20 amp cord is not factory and added on.

That RV was built to only run one AC on shore power, ( the selector switch ) or both on generator. The added cord is most likely for the second AC only.

Yes, the 50 amp to 2 30 amp splitter will work for you, and so will 2 seperate circuits in your house.

The question is how the 20 amp cord is tied into the generator 20 amp circuit.
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Old 06-21-2021, 09:39 AM   #3
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Thanks for the information. How can you be sure the 20 amp circuit was added on? Personally I never thought RVs would have both a 30 amp plug and a 15/20 amp plug, but after research I see some do have this. But you're sure mine was added? Is it because you know this model didn't have it from the factory? Or because RVs from that era just never had it?

I know it's hard for you to tell, but even if this is after market, how can a rig make use of a 30 amp receptacle and a 15/20 amp receptacle at the same time? Because the rig functions completely with the 30 amp alone, how could one wire this setup so plugging in the extra 15 amp plug would even do anything (extra, I mean)? I have a good understanding of physics but electrical wiring is not my specialty. Thanks again.

Edit: let's suppose you're correct that the 20 amp plug was added primarily for running both AC units at once while on shore. Does this have any affect on other appliances I might want to use? For example, suppose I plug the 30 amp and 20 amp on separate circuits. let's say I turn on the refrigerator (let's say 1000 watts) and one AC unit (2000 watts), and maybe some other stuff (5000 watts) for a total of 8000 watts. Would this work, as it my RV had a 50 amp plug? I'm assuming not.
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Old 06-21-2021, 09:44 AM   #4
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In most cases where owners added a 15/20 shore power "system" it was to power a second A/C.


Are you sure everything 120 VAC on your coach works without plugging in the owner-added 15/20?
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Old 06-21-2021, 10:01 AM   #5
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Originally Posted by wolfe10 View Post
In most cases where owners added a 15/20 shore power "system" it was to power a second A/C.


Are you sure everything 120 VAC on your coach works without plugging in the owner-added 15/20?
So far, everything has worked on the 30 amp plug in alone. Both AC units will function separately (not at once) on the 30 amp plug. But when I turn the other one, the first one turns off. All 120V receptacles in the unit work.

This rig doesn't seem to have a whole lot of things added on after the fact. There is an on off switch (like a light switch) inside the storage bay next to the water heater, and I don't know what it does. There are a couple of on off switches in the cabin area near Otherwise, most things appear to be stock (solar panel set up, inverter, etc.).

Are you suggesting there is a separate circuit which functions on this 15/20 plug, completely independent of everything else? Along with a separate circuit breaker panel? Stupid question, but where is the breaker panel anyways?
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Old 06-21-2021, 10:06 AM   #6
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Originally Posted by DarkVader View Post

Are you suggesting there is a separate circuit which functions on this 15/20 plug, completely independent of everything else? Along with a separate circuit breaker panel? Stupid question, but where is the breaker panel anyways?

Since this was extremely likely to have been installed by a previous owner rather than OE from the factory, it is going to be really hard for us to know what he did.
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Old 06-21-2021, 10:17 AM   #7
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Since this was extremely likely to have been installed by a previous owner rather than OE from the factory, it is going to be really hard for us to know what he did.
Is it a "common" upgrade for people to add a separate 15 amp receptacle to help power specific things on the rig? Or for other reasons? Again I know you won't be able to tell, but why do people usually add something like this, given that we know everything works on the single 30 amp plug in?

If I look at the breaker panel, will this help figure this out? One thing I notice is that when plugged into shore power (30 amp), there is a noticeable hum coming from under the bed. Kind of annoying, maybe it's related? No appliances on, inverter off. Also might relate to this on/off switch in the storage bay...trying to figure all this out...
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Old 06-21-2021, 10:23 AM   #8
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The modification was usually made to allow use of both roof A/C's at the same time along with other 120 VAC loads.
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Old 06-21-2021, 10:36 AM   #9
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The modification was usually made to allow use of both roof A/C's at the same time along with other 120 VAC loads.
Will check this out when I get back to the motorhome. If this was the case, I'm curious how an old rig like this "knows" when both are plugged in. I mean, how does it know that I can run both ACs when both plugs are plugged in? I ask because they do function each independently and I don't see how plugging it in would allow both to work (since there isn't much of a computer on board).

And if this was the purpose of this plug, it would be beneficial at least for using both ACs on shore power (so it would be worth while paying for a 50 amp plug at a park, and buying a Y splitter, 50 amp to two 30 amps, and using an adapter (30 amp to 20 amp) on one of the Y ends). Anything is possible, but is it likely that this extra plug would benefit me in other ways, like running other appliances all at once? Hard to know I understand, but I feel it's highly unlikely it would benefit other electrical uses. Is the breaker panel usually under the bed?
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Old 06-21-2021, 10:46 AM   #10
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I would expect that the 20 amp cord goes to some specific device or outlet that a previous owner wanted power to, not to any sort of a breaker box. You'll need to follow that cord to see what it does. Or unplug the 30 amp cord and see what works with the 20 amp cord plugged in. While we interested in hearing the outcome, I don't think there is anyone here who can answer your question of what that cord does, because it does whatever the previous owner wanted it to do. We're 99% certain that isn't part of the original setup of your RV.
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Old 06-21-2021, 12:30 PM   #11
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You probably have a 5500 watt generator. They are used to power both air conditioners.

It will have 2 circuit breakers on it, one 30 amps and another 20 amps, just for the second air conditioning.

That power is controlled by auto transfer switchs. PO just needed to cut into that 20 amp circuit and add another Auto switch.

By the way, 50 amp service is 12,000 watts. Its 50 amp@ 120/240 volts.
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Old 06-21-2021, 04:43 PM   #12
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I just wish I had a 30 amp hook up at home to test! Right now best I can do is plug both into regular 15 amp receptacles on separate circuits. I do have a 50 amp range plug nearby but I don't know how my RV was wired so I don't want to break anything by getting a 50 amp Y splitter and trying to plug the two RV plugins to the splitter...

Yes I really wish my unit had a dedicated 50 amp hookup. 50 amps on each 120v end would help us out a lot more when it gets really hot, being able to run both ACs from shore power, along with the fridge and a few other things, would have been nice.

Yes, the genny has exactly what you mentioned, two breakers.
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Old 06-21-2021, 04:59 PM   #13
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Very likely your 50 amp house outlet is the SAME.


To test:


Two outer straights are the hots (L1 and L2)
Center straight is neutral.
Center round is ground.


So either outer straight to either center= 120 VAC
Outer straight to outer straight= 240 VAC
Center straight to center round= 0 VAC
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Old 06-21-2021, 05:04 PM   #14
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Originally Posted by wolfe10 View Post
Very likely your 50 amp house outlet is the SAME.


To test:


Two outer straights are the hots (L1 and L2)
Center straight is neutral.
Center round is ground.


So either outer straight to either center= 120 VAC
Outer straight to outer straight= 240 VAC
Center straight to center round= 0 VAC
Oh yes it's the right outlet. I just don't have an actual 50 amp plug on the RV. I only have the 30 amp and then the 20 amp. I know it was mentioned I can plug into the Y splitter earlier, but is that safe when I don't know how the rig is wired right now? We all know people who have tried to plug their 30 amp into a dryer outlet and...well that's not how it works
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