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Old 07-14-2017, 06:16 PM   #29
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Airstreams don't have 240VAC systems...
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Old 07-14-2017, 07:10 PM   #30
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Originally Posted by sheriff1 View Post
Airstreams don't have 240VAC systems...
Yes they do.
Any 50 amp RV is 240v, not 120v. Only if it is 30 amp is it 120v.
If you order a new Airstream from the factory with two air conditioners is does have a 240 v electric system.
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Old 07-14-2017, 08:38 PM   #31
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Yet another generator question...2 AC Units

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Originally Posted by A W Warn View Post
Yes they do.

Any 50 amp RV is 240v, not 120v. Only if it is 30 amp is it 120v.

If you order a new Airstream from the factory with two air conditioners is does have a 240 v electric system.


You don't know what you are talking about ! There are no 240 devices onboard. You have 2 legs each 120vac.
Yes, the outlet you plug in to is wired the same as a 240 outlet but that's where it ends. Proof of this is if you use a 50 to 30 amp adapter everything in the rv will work ( not at the same time) but the entire system is 120vac.
(Retired power company employee )
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Old 07-15-2017, 09:24 AM   #32
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Originally Posted by sheriff1 View Post
You don't know what you are talking about ! There are no 240 devices onboard. You have 2 legs each 120vac.
Yes, the outlet you plug in to is wired the same as a 240 outlet but that's where it ends. Proof of this is if you use a 50 to 30 amp adapter everything in the rv will work ( not at the same time) but the entire system is 120vac.
(Retired power company employee )
Hi

You are missing one very important fact. The connection to the trailer is done with a 50A connector and cabling rated for 50A. It's set up as a 240V circuit so the "two 120V" circuits are 180 out of phase with each other. If you put a voltmeter across the two hot leads, they most certainly *do* read 240.

Since the two circuits are 180 out of phase, with both fully loaded (resistive loads) you have zero current in the neutral. If you have one loaded and the other with no load, you have 50A down the neutral (still fine).

Wire the beast up with "two 120V circuits" in phase and things are a bit more messy. With only one side loaded you have 50A down the neutral just like you did before. With both sides loaded, the current is now in phase, you have 100A down the neutral. That is beyond the rating of the cable or the connector. Worse, since it's in the neutral, there is no fuse or breaker to protect you. You have a very real risk of fire.

A 30A adapter works fine because the neutral *is* rated for 50A. In that case, noting is running over ratings. No smoke, no fire.

If it was a 120V only circuit, we'd call it a 100A hookup ....

Why go on and on about this? It's a very common misconception. If Bubba is wiring up a socket for the RV and gets it wrong ... you can have a fire. The fire could be in his RV. If he works at a campground, it could be in my RV. That's why one needs to be very clear about what should be on those wires.

Bob
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Old 07-15-2017, 03:46 PM   #33
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240v

Quote:
Originally Posted by sheriff1 View Post
You don't know what you are talking about ! There are no 240 devices onboard. You have 2 legs each 120vac.
Yes, the outlet you plug in to is wired the same as a 240 outlet but that's where it ends. Proof of this is if you use a 50 to 30 amp adapter everything in the rv will work ( not at the same time) but the entire system is 120vac.
(Retired power company employee )
No need to be upset. We all are trying to help each other, at least that is my goal.

I did not say there was a 240v appliance in an Airstream. I said there was a 240 volt system, the service that feeds the trailer is 240 volt. Two 120v legs create a 240 volt system. There are two buss bars inside the electrical panel energized seperately by each 120v leg.

If a person would connect a 240v appliance to the shore power pedestal it would function correctly because it is a 240v outlet.

The second air conditioner will not work when using the 50 to 30 amp adapter because it is on a separate buss from every other circuit. This is clearly shown on the electrical schematic drawings for the Airstream trailers with two air conditioners, those that are included in the owners manuals.
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Old 07-16-2017, 07:06 AM   #34
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Wow, so much info and I'm as confused as ever, ha!! I think running one AC on a generator will suffice as most of the boondocking will be done in cooler weather. Our trailer is a 30 amp by the way.
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Old 07-16-2017, 07:58 AM   #35
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Originally Posted by A W Warn View Post
Trailers with 2 AC units come from the factory with 50 amp 240v system.
No.
Trailers with 2 AC units come from the factory with 50 amp 125v. system. Yes, the power post in the Park is wired the same as 240v., however inside the Airstream (and almost every RV) the two hots are never used together. So the result is TWO separate 50 amp 125v. legs each independent of the other.
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Old 07-16-2017, 08:32 AM   #36
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Originally Posted by A W Warn View Post
No need to be upset. We all are trying to help each other, at least that is my goal.



I did not say there was a 240v appliance in an Airstream. I said there was a 240 volt system, the service that feeds the trailer is 240 volt. Two 120v legs create a 240 volt system. There are two buss bars inside the electrical panel energized seperately by each 120v leg.



If a person would connect a 240v appliance to the shore power pedestal it would function correctly because it is a 240v outlet.



The second air conditioner will not work when using the 50 to 30 amp adapter because it is on a separate buss from every other circuit. This is clearly shown on the electrical schematic drawings for the Airstream trailers with two air conditioners, those that are included in the owners manuals.


Haven't looked at the schematic but I can tell you for a fact that with a 50 to 30 amp adapter either AC will run. Everyone needs to be aware of this because it could create a potential hazard.
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Old 07-16-2017, 08:34 AM   #37
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No.

Trailers with 2 AC units come from the factory with 50 amp 125v. system. Yes, the power post in the Park is wired the same as 240v., however inside the Airstream (and almost every RV) the two hots are never used together. So the result is TWO separate 50 amp 125v. legs each independent of the other.


Exactly! Some of the new large motor homes do take advantage of the 240 potential and are true 240 service.
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Old 07-16-2017, 09:04 AM   #38
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Yet another generator question...2 AC Units

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Originally Posted by uncle_bob View Post
Hi...

Since the two circuits are 180 out of phase, with both fully loaded (resistive loads) you have zero current in the neutral...

Bob


That is true for 240v systems, the neutral can be cut and everything will still work.

Cutting the neutral on a 50A Airstream results in no power to anything.

On edit, a low amp load on one leg and a high current load on the other with neutrals tied but not hooked to the post causes big problems. The low current device will see over 120v due to the unbalanced load. The neutral does see a load in the Airstream.
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Old 07-16-2017, 11:02 AM   #39
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Wow, so much info and I'm as confused as ever, ha!! I think running one AC on a generator will suffice as most of the boondocking will be done in cooler weather. Our trailer is a 30 amp by the way.
If your trailer has only 30 amp 120v electric system it will have problems running both AC units at the same time, whether generator or shore power (assuming they have not been modified). When two AC units start at the same time the current draw would exceed the capacity of the electrical system, which could trip breakers and/or might damage the AC units. The addition soft start system that was recommended in a post above would be a good idea in this case (reducing the current draw at startup).

I have heard of people running a second 20 amp electric cord for a rear air conditioner that plugs in separately from the 30 amp electric cord. I'm curious to find out if this is what your trailer might have.

When you receive the trailer will you follow up with comments about how the system functions?
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Old 07-17-2017, 06:28 AM   #40
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That is true for 240v systems, the neutral can be cut and everything will still work.

Cutting the neutral on a 50A Airstream results in no power to anything.

On edit, a low amp load on one leg and a high current load on the other with neutrals tied but not hooked to the post causes big problems. The low current device will see over 120v due to the unbalanced load. The neutral does see a load in the Airstream.
Hi

Bingo !

The system in your house that is called "240V" has two 110V legs to ground. Your AS is wired exactly the same way. The proper term for the system is 240V in your house. The proper term for it in your RV is a 240V *system*. You don't always plug everything into 240V in your house, you don't do that in your RV either. That does not change the type of system it is.

If you cut the neutral to your house, things get weird in a hurry. Same thing if you cut the neutral to an RV. In both cases - don't do it, you'll damage things. It also really freaks people out. I've seen it happen enough times to know.

Your house has a 200A 240V service wired into it. That gives you 400A if you use it as 120V. Your RV has a 50A 240V service wired into it. You get 100A if you use it all at 120V.

On your house the power company brings in a bundle of wires. Those attach here and there. They eventually get to your breaker box. You don't plug your house in. Your RV does have a plug. Until the neutral comes loose at the meter, you don't think much about how the power company hooked up your house. Because you have a plug and go around hooking up your RV to who knows what, you *do* need to understand how your RV should be hooked up.

It's a safety issue ... it's important !!!

Bob
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Old 07-17-2017, 07:33 AM   #41
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Wow, so much info and I'm as confused as ever, ha!! I think running one AC on a generator will suffice as most of the boondocking will be done in cooler weather. Our trailer is a 30 amp by the way.
If you have two A/C units then the system is 50 amps. Good luck and enjoy. I see we are neighbors ( in geological terms &#128514 My Briggs P3000 runs my A/C very well and I plan to increase the system with the P 2200. My P3000 was about 900$ less than the Honda version.
Thomas
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