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Old 04-15-2008, 09:50 PM   #1
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Rear Air and 50 Amp

I hate to bring up a 50 amp question since most SOB threads end up debating whether it is really 100 amps or 50 amps. Let's state right up front that a 50 amp connection at the pedestal is 50 amp on leg 1 and 50 amp on leg 2 for a total of 100 amp 110v service. Most class A's put some circuits on leg 1 and some on leg 2. A few high end rigs have some 240v appliances but most don't.

Now Airstream has a bedroom ac option and 50 amps. What is the outside connection? A normal 50 amp connector? If so, does Airstream use just one leg of the 50 amp service?

I know there are other ways to hook up the rear ac using a separate outside 30 amp connection. But let's discuss the way Airstream does the factory option.

Barry
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Old 04-16-2008, 10:08 AM   #2
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If Airstream provides outside a normal 50 amp connector, then it is possible the rear ac is on leg 2 and the rest of the circuits on leg 1. If I have 50 amp at the site, everything is normal. If 30 amp is the max available, then using a 30 to 50 amp adapter provides a total of 30 amps across both legs (my understanding of how the adapter works). So either ac can be used, just not both at the same time.

Barry
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Old 04-16-2008, 10:24 AM   #3
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I have both a 50 amp and a 30 amp power cord. I can run both units with 50 amps. I can run either unit with 30 amps. I can run 1 ac compressor and the other ac fan with 30 amps in either combonation. Based on that informataion the power cord supplies the panel box in such a way that both ac units can be powered with either 50 or 30 amp service
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Old 04-16-2008, 10:26 AM   #4
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Quote:
Originally Posted by pattonsr
If Airstream provides outside a normal 50 amp connector, then it is possible the rear ac is on leg 2 and the rest of the circuits on leg 1. If I have 50 amp at the site, everything is normal. If 30 amp is the max available, then using a 30 to 50 amp adapter provides a total of 30 amps across both legs (my understanding of how the adapter works). So either ac can be used, just not both at the same time.

Barry
Hi Barry,

I'd say that's true that if you're wired for 50 amp, with only 30 available. However, many folks with native 50 amp service do utilize an adapter allowing them to combine the 30 amp along with the 20 amp circuit commonly found alongside it, to enable them to run both A/C's simultaneously. In most cases, you probably could get away with just a 30 amp adapter, and then just running the fan only on one of the two units, as Rick mentioned.

In the event of one adding a second A/C (which I'm doing in the next couple of months), I'll just run a separate circuit for the rear A/C, which will utilize that available 20 amp connection at the site.
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Old 04-16-2008, 10:33 AM   #5
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In my previous unit I installed a second ac in the bedroom. I had a dedicated 20 amp service with breaker and a seperate power cord that used the 20 amp circuit on the power pole. I never had an issue with this set-up. Others in the club have similar set-ups and they haven't had issues either.
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Old 04-16-2008, 10:37 AM   #6
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Originally Posted by Tarheel
In my previous unit I installed a second ac in the bedroom. I had a dedicated 20 amp service with breaker and a seperate power cord that used the 20 amp circuit on the power pole. I never had an issue with this set-up. Others in the club have similar set-ups and they haven't had issues either.
This is true; in fact, I'm doing mine the way you did yours. I still have the pics of it you sent me.

What'll be nice is still having some A/C while biscuits are baking in the convection microwave!
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Old 04-16-2008, 11:04 AM   #7
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Its also nice to have ac and carry on a conversation or watch tv without entertaining the entire campground. I tend to talk over the AC and get that special look from wife, so sometimes the rear ac keeps me out of trouble for a few moments anyway.
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Old 04-16-2008, 01:11 PM   #8
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I don't have any firsthand knowlege of how Airstream does this, but I do know that the NEC allows either 30amp 120vac or 50amp 120/240vac.

If it is 50amps 120/240vac, it is required that the load distribution center provide a reasonable current balance between the phases. So that would tend to speak against running a single leg 50 amp service.

However (and here's the kicker) it's not prohibited to make it that way. So you can wire it as 50 amps 120vac if you want, but I doubt that Airstream would do it that way. Just doesn't seem right. And you would need a 50 amp 120/240vac plug anyway to hook up to a common campsite service.
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Old 04-21-2008, 11:49 AM   #9
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I have some final questions/thoughts based on some of the comments.

Rear ac powered by a separate circuit. In campgrounds that have a box with 20 and 30 amp receptacles, isn't the breaker in the main box usually 30 amp? If so, wouldn't using both the 20A receptable and the 30A receptable to run both ac's at the same time trip the breaker?

Front and rear ac powered by 50 amp. In a 30 amp campground, it has been suggested using a cheater box to combine the 30 and 20 amp. Since most 20 amp receptables are GFI, the cheater wouldn't work. If the 20 amp receptable wasn't a GFI, then one would have the same probem as I described above if the main breaker on the box was 30 amp.

It seems to me the cheater box is most useful if I can find another 30 amp or 20 amp nearby that is on a different breaker. And if I get 240v across both legs of the cheater box 50 amp receptacle, then I will not be overloading the neutral.

Barry
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Old 04-21-2008, 12:27 PM   #10
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Hi Barry,

It's been my experience that most RV service panel boxes have individual breakers for each circuit within the box. Though I'm no electrical engineer (and haven't stayed in a Holiday Inn Express in quite some time), I'd imagine the common neutral within the box at a 30 amp campsite, provided all power is delivered to the box by a single power source, would have the capacity to deal with the combined amperage (30+20) of both circuits. I'm not sure how the GFCI-protected circuit would figure in with regards to the cheater box, since I haven't personally used one, but I have observed them in use. I've never seen additional nearby 30 or 20 amp circuits beyond those of an adjacent campsite - and I expect the occupant of that site might get kinda peeved if someone came over and helped themselves to the juice.
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Old 04-22-2008, 10:31 AM   #11
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Can someone chime in on the usefulness of a cheater box to combine the 30 amp and the 20 amp. Are most 20 amp connections GFCI? All the cheater box ads including the one I have say they won't work with GFCI.

Barry
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