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Old 02-24-2013, 12:42 PM   #1
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50 Amp Service has to be 240v

Since I'm not aware of any 240 volt requirements in an RV (such as for a clothes dryer outlet), I had been wondering if it was ok to just bring in two 120v, 50-amp circuits. It seems like nothing in the RV would know the difference.

I figured out why that is NOT an acceptable approach.

In summary, it's because the neutral wire in your RV isn't sized for 100 amps of current.

In order to maintain 50 amps or less in that neutral wire, it's necessary that the two circuits have opposite phase across that neutral. This means that when one circuit is moving electrons into the neutral, the loads on the other circuit are taking at least some of those electrons out of the neutral. Neglecting minor phase-shifts (which happen when motors are involved), if each circuit is drawing 30 amps, the current in the neutral wire back to the pedestal has zero amps. The worst-case current in the neutral occurs when one circuit is pulling 50 amps and the other is pulling 0 amps.

I just thought this was interesting. I wonder if any of the "surge protection" devices actually check that there is ~240v between line-1 and line-2, because that is really important! I think I'll find out.
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Old 02-24-2013, 01:41 PM   #2
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You are absolutely correct regarding the two phases opposing each other, and therefore reducing the neutral current.

That being said, consider the fact that when a 50A to 30A adapter is used, it place the same phase on both sides of the 50A plug. BUT, you are then limited to 30A max by the pedestal breaker.

Here's a chart that might help you determine what protection some of the most commonly used SPs have.

RV Surge Protector Comparison

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Old 02-24-2013, 01:50 PM   #3
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Good point. I guess that answers the question as to whether the surge-protectors check for this: They can't (and allow adapters).
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Old 02-24-2013, 02:45 PM   #4
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The progressive has to be bypassed in order to use 30 amp service.
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Old 02-24-2013, 03:09 PM   #5
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Quote:
Originally Posted by garbonz View Post
The progressive has to be bypassed in order to use 30 amp service.
Really? From their web FAQ's:

"Can I use an adapter and maintain full protection?
Yes. An adapter can be used and the RV will maintain full surge protection."

I was going to find out from experience on Wednesday. Thanks for the heads-up.
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Old 02-27-2013, 08:51 PM   #6
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The current EMS-HW50's don't need to be bypassed. They work just fine on a 30->50 adapter. I suspect Progressive would update yours if you asked.
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Old 02-28-2013, 08:55 AM   #7
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I am now even more impressed with Progressive Industries.

On the day that I posted the original comments I also sent an email to Progressive Industries asking if they had a check to insure there were two phases (~240v) between the two lines.

When RodeoGeorge posted with the need for adapters to be supported, I sent another email, suggesting that they check for single phase AND total line currents over 35 amps (which works in both situations).

I received a reply (from the president of the company no less!) saying that they had a new design which addresses my concern, but that it wasn't ready yet. He offered to upgrade my unit if I was interested.

I call that excellent customer service!!
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Old 02-28-2013, 10:03 AM   #8
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Thanks for posting this info Barry, Garbonz and Wa3pnt! I'm researching a 50 amp hard wired surge protector and know nothing about electrical. We have 50 amp service in our 5'er but sometimes use sites with 30 amp so the info you posted answered one of my questions. Based on what I've read on this forum, Progressive Industries is the way to go.
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