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Old 06-20-2020, 09:09 PM   #41
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Originally Posted by Fish and Dear View Post
Would this actually work?Attachment 24233

You're going to need to know how your vehicle (and every AC appliance in it) is wired in order to answer with certainty. You're also going to need to know how the pedestal is wired.

It's possible that the pedestal is powered with a single 120V, 30A feed that is fused at the source at 30A or 40A. Therefore, the same 120V leg is the source for both the 15A and 30A receptacles. In this case, trying to fully load both receptacles will blow the breaker at the source (30A+15A is greater than the feed breaker) and cause the campgrounds owner to wonder what's going on (why didn't the campsite breaker trip instead of his 40A breaker?).

Maybe the feed is 120V single leg, fused at 50A and the feed wire gauge supports this amperage. In this case, you will be able to get the 45A, but this again is just a single leg from the source. Any appliance that runs off of 240V will not work, and I don't like the idea of running the same leg/phase to both legs on that appliance - it obviously won't work, but even if it's not in use..

If the feed uses both legs of the 240V mains (one for the 30A, and one for the 15A), then you have a decent chance of things working fine on any RV as long as you don't exceed the current limit on the 15A leg. I still don't like this much, as an overload could only pop the 15A breaker. So a 240V appliance in the RV can feed voltage from the live leg to the dead one. This can result in all kinds of strange voltages (less than 120V) which could possibly damage certain equipment in this brown-out state. This is why 240V breakers have both breaker legs mechanically tied together - one side failing trips the whole thing.

Why is GFCI not supported? 120V GFCI's constantly (millisecond by millisecond) compare the current flowing out_of_the_HOT_wire to the current returning into_the_NEUTRAL_wire, and vice-versa. If those currents don't match within 10mA (0.01A) or so (as in someone holding the HOT wire while grounded), the GFCI breaker will trip. Using this adapter can allow current to go directly from one AC leg to the other (through a 240V load), bypassing the GFCI's neutral path altogether, which would result in several AMPS of imbalance on the GFCI, thus it trips immediately, leaving you with only the the leg that doesn't have a GFCI as well as the potential brown-out situation that I mentioned above. The adapter (depending on how it's actually wired) could also feed current from the 30A leg into the GFCI's neutral wire, which would cause a 15A GFCI trip from a 120V appliance running normally on the 30A leg.

Regarding 45A being enough POWER to run multiple A/C units, etc: Amps is not power, WATTS is (are). The reason that larger RV's adopt 50A service over 30A is not because it increases the power by a factor of 50/30 (1.6 times), but because it increases by [50Ax240V (12,000W) divided by 30Ax120V (3,600W)], or 3.33 times. So, the 45A example can power 5.4KW [(15A + 30A) x 120V] worth of equipment, versus the 12KW from a proper 50A pedestal.

Why do they use 240V appliances then, when they can cause these issues? Lower current. For a given power requirement, higher voltage means lower current (power = voltage times current). Lower current means smaller wire size, smaller connector pins, and less heat and power loss in the power delivery system.
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Old 06-20-2020, 10:07 PM   #42
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You're going to need to know how your vehicle (and every AC appliance in it) is wired in order to answer with certainty. You're also going to need to know how the pedestal is wired.

It's possible that the pedestal is powered with a single 120V, 30A feed that is fused at the source at 30A or 40A. Therefore, the same 120V leg is the source for both the 15A and 30A receptacles. In this case, trying to fully load both receptacles will blow the breaker at the source (30A+15A is greater than the feed breaker) and cause the campgrounds owner to wonder what's going on (why didn't the campsite breaker trip instead of his 40A breaker?).

Maybe the feed is 120V single leg, fused at 50A and the feed wire gauge supports this amperage. In this case, you will be able to get the 45A, but this again is just a single leg from the source. Any appliance that runs off of 240V will not work, and I don't like the idea of running the same leg/phase to both legs on that appliance - it obviously won't work, but even if it's not in use..

If the feed uses both legs of the 240V mains (one for the 30A, and one for the 15A), then you have a decent chance of things working fine on any RV as long as you don't exceed the current limit on the 15A leg. I still don't like this much, as an overload could only pop the 15A breaker. So a 240V appliance in the RV can feed voltage from the live leg to the dead one. This can result in all kinds of strange voltages (less than 120V) which could possibly damage certain equipment in this brown-out state. This is why 240V breakers have both breaker legs mechanically tied together - one side failing trips the whole thing.

Why is GFCI not supported? 120V GFCI's constantly (millisecond by millisecond) compare the current flowing out_of_the_HOT_wire to the current returning into_the_NEUTRAL_wire, and vice-versa. If those currents don't match within 10mA (0.01A) or so (as in someone holding the HOT wire while grounded), the GFCI breaker will trip. Using this adapter can allow current to go directly from one AC leg to the other (through a 240V load), bypassing the GFCI's neutral path altogether, which would result in several AMPS of imbalance on the GFCI, thus it trips immediately, leaving you with only the the leg that doesn't have a GFCI as well as the potential brown-out situation that I mentioned above. The adapter (depending on how it's actually wired) could also feed current from the 30A leg into the GFCI's neutral wire, which would cause a 15A GFCI trip from a 120V appliance running normally on the 30A leg.

Regarding 45A being enough POWER to run multiple A/C units, etc: Amps is not power, WATTS is (are). The reason that larger RV's adopt 50A service over 30A is not because it increases the power by a factor of 50/30 (1.6 times), but because it increases by [50Ax240V (12,000W) divided by 30Ax120V (3,600W)], or 3.33 times. So, the 45A example can power 5.4KW [(15A + 30A) x 120V] worth of equipment, versus the 12KW from a proper 50A pedestal.

Why do they use 240V appliances then, when they can cause these issues? Lower current. For a given power requirement, higher voltage means lower current (power = voltage times current). Lower current means smaller wire size, smaller connector pins, and less heat and power loss in the power delivery system.
Good recap of the entire thread. You did read the entire thread didn't you?
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Old 06-20-2020, 10:55 PM   #43
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Thanks! And yes, but I didn't mention extension cords or dog bones.
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Old 06-22-2020, 04:03 AM   #44
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Would this actually work?Attachment 24233

It gives you 30 amps on one leg and 20 amps on the other leg of your 50 amp plug. And as mentioned will probably trip the CGFI if equiped
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Old 06-22-2020, 04:27 AM   #45
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Somebody please kill this thread!
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Old 06-22-2020, 08:09 AM   #46
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Somebody please kill this thread!
But it was just getting fun...
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Old 06-22-2020, 04:00 PM   #47
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Perhaps Im reading too much into the need for one of these 30+15 to 50 Amp adaptors in the first place, but it seems that the main driver is being able to power 2 air conditioners simultaneously on rare occasions. Id have to assume that owners of 50A rigs normally request 50A campsites when available.

Anyway, if you think youll be using a 30A pedestal frequently, wouldnt it be more effective to re-wire one of the two Air Conditioners so it can run off 50A or be plugged in directly to the pedestal?

Some owners on this forum who have added a second A/C on 30A motorhomes essentially do that. It would take a bit more work initially on a 50A rig to have the option built in, but would provide more operational flexibility in the long run.
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Old 06-22-2020, 08:37 PM   #48
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On a typical 50 amp coach (yeah I know no such thing as typical) what happens when you plug into a 30 amp outlet. Do all the circuts that are on the other hot lead just not work? Or is there a transfer switch that adapts to single leg vs two legs?
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Old 06-22-2020, 08:53 PM   #49
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On a typical 50 amp coach (yeah I know no such thing as typical) what happens when you plug into a 30 amp outlet. Do all the circuts that are on the other hot lead just not work? Or is there a transfer switch that adapts to single leg vs two legs?
When you plug a 50 amp coach into a 30 amp ped You apply the 30 amp circuit down both legs. Everything in the 50 amp RV is on 1 30 amp leg. You will trip at 30 amps usage. you do not get 240 to the panel as you would if plugged in to a 50 amp receptical.
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Old 06-22-2020, 08:55 PM   #50
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Thanks
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Old 06-22-2020, 09:37 PM   #51
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Im not 100% certain on this, but believe that Onan 5,500 Watt generators that are very common on many 50A motorhomes are wired the same way so that L1 and L2 are fed by same 120V generator. The 5500-Watt generator can supply more than 30A though.
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Old 06-22-2020, 10:13 PM   #52
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Im not 100% certain on this, but believe that Onan 5,500 Watt generators that are very common on many 50A motorhomes are wired the same way so that L1 and L2 are fed by same 120V generator. The 5500-Watt generator can supply more than 30A though.
I think you meant "same winding", obviously they are fed by the same generator. My understanding is that two lines are in-phase; one through a 30 amp breaker and the other through a 20 amp breaker.
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Old 06-22-2020, 10:45 PM   #53
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Perhaps Im reading too much into the need for one of these 30+15 to 50 Amp adaptors in the first place, but it seems that the main driver is being able to power 2 air conditioners simultaneously on rare occasions. Id have to assume that owners of 50A rigs normally request 50A campsites when available.

Anyway, if you think youll be using a 30A pedestal frequently, wouldnt it be more effective to re-wire one of the two Air Conditioners so it can run off 50A or be plugged in directly to the pedestal?

Some owners on this forum who have added a second A/C on 30A motorhomes essentially do that. It would take a bit more work initially on a 50A rig to have the option built in, but would provide more operational flexibility in the long run.
Yes, typically the 'two air conditioners at the same time' is what drives many of us 50amp coach owners to try to 'find' more than the typical 30amp power, when that's all that's available, at least in a standard plug configuration. The adapter makes the 'combo' of the 30amp and 20amp outlets provide a more robust amperage available for those who 'want' more power - two air conditioners AND other things, etc., usually during the heat of the summer, but also sometimes it's quite convenient during winter when wanting to use 'all electric' appliances versus so much propane, such as plug-in electric heaters, which certainly can trip breakers when not managed properly.
Having said that, two 13.5 kw 'typical' size roof air conditioners 'can' be powered easily by a 30amp RV outlet, but what happens to most is that there is a disconnect between what 'silent' power usage is happening at the same time, such as the electric water heater, the battery charger, a hair dryer, the microwave, which then most easily trips the breaker, making the owner think that the '30amp for two air conditioners' is not possible, though it certainly is. When you are used to 50amp RV service, though, dealing with this 'inconvenience and aggravation' is why some of us resort to trying 'adapters' to make up some of the difference. They DO work, and they ARE convenient, although their usage might be very infrequent - it's just VERY enjoyable when you DO have that option!

As for 'rewiring' one of the existing roof air conditioners to be able to be powered by an additional external outlet is an idea, and if someone is in a position where they will be parked for very extended summer months at a location where there is only a 30amp and 20amp outlet, then that's an idea, although the work to do it might scare away most RV owners from tackling this. Since your roof air conditioners are hardwired into the existing Main Panel of the RV, it's not a simple task to 'undo' that wiring, add additional wiring necessary to reach an external outlet, and a 120v male plug end, all while realizing that now you've removed this second air conditioner from your RV's main panel, and it will not be powered any longer from the 50amp panel, from a 50amp RV outlet, or from the generator. That might not be a choice most want to relegate themselves to.
Many 30amp RV owners, though, want to add that second roof a/c unit and have it powered externally since their RV's Main Panel is already not designed to handle it. It gives them an option, when parked, that they don't have when traveling with the generator, anyway....so, it's a win-win.

There are certainly MANY things that RV owners can do, and have done, even though most RVrs wouldn't tackle such things, since most RV owners are simply weekenders, or use their RVs infrequently. Those of us who travel extensively, though, and basically LIVE in our RV either full-time, or much of the time, certainly want the OPTIONS when those situations arise where electricity is not available, or the same Amperage of power is not available, which is really much more common than not. Having a 'choice' of a 50amp RV site is not also an option, many campgrounds only have 30amp service, and even those with 50amp service don't have EVERY site with that power option.

ENJOY! : ) It's FUN!
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Old 06-22-2020, 10:50 PM   #54
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I think you meant "same winding", obviously they are fed by the same generator. My understanding is that two lines are in-phase; one through a 30 amp breaker and the other through a 20 amp breaker.
Thanks. Meant the versus same. I should proof read better when making revisions. My bad.


I know some larger generators can supply 240V power so that L1 and L2 can operate as intended while plugged into 50A pedestal. The limit is 50A so I assume any generator above 6,000 Watts must be 240V.
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Old 06-22-2020, 10:52 PM   #55
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when you get up to the 10kw models and higher they offer 120v and 240v output
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Old 06-22-2020, 11:12 PM   #56
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.....cut.... Since your roof air conditioners are hardwired into the existing Main Panel of the RV, it's not a simple task to 'undo' that wiring, add additional wiring necessary to reach an external outlet, and a 120v male plug end, all while realizing that now you've removed this second air conditioner from your RV's main panel, and it will not be powered any longer from the 50amp panel, from a 50amp RV outlet, or from the generator. That might not be a choice most want to relegate themselves to. .....cut.....

That’s not the way I would do it, nor did I suggest “removing A/C” from 50A service or generator.

I tried to emphasize “or” option in “Anyway, if you think you’ll be using a 30A pedestal frequently, wouldn’t it be more effective to re-wire one of the two Air Conditioners so it can run off 50A “or” be plugged in directly to the pedestal?”

On second thought, it wouldn’t be much more difficult so that “either” A/C (one or the other) could be powered from 20A separate source, providing even more flexibility.
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Old 06-22-2020, 11:25 PM   #57
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maybe I'm a little confused by your question, or explanation in your response, but the reason that you can't just 'power' one of the roof air conditioners on a 50amp coach via 'another' power source is that you are effectively then removing it from the primary power sources - the 50amp Main Panel circuit breakers via shore power or the generator.
The reason is, you can't have 'two' power sources for the same appliance without an additional ATS( Auto transfer switch) dedicated solely for that appliance, or some way to 'unplug' from one source and 'plug into' another one - not an easy task, and why most of us use an ADAPTER, to make use of a 30amp and 20amp outlet, to simply this situation.
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