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Old 09-23-2017, 04:34 PM   #1
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30 amp or 50 amp

I recently pulled into a site and the 30 amp plug had an open ground. I have a 30 amp rig. The host could not get maintenance until the next day. I checked the 50 amp and found it to be fine so plugged into 50 amp and used it. The next day the electrician? Came and changed out the 30 amp plug and problem solved. He recommended that I always use the 50 amp outlet when available. I know the main 30 amp breaker in the motorhome should protect the electronics, etc. The question to those electric minded individuals. Is it a good general practice to use the 50 amp circuit with an adapter to run my 30 amp coach? I don't have a fancy electric monitor system (on the wish list) just a cheap surge protector. Thanks in advance for your advice.
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Old 09-23-2017, 04:45 PM   #2
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I like to keep things simple: plug into, and use what your rig wants... (30 amps for your case...)
But that's just me I do this because I'm as ignorant about 'lectricity; as Hogs are about the Sabbath!
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Old 09-23-2017, 05:12 PM   #3
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Originally Posted by Bob Denman View Post
I like to keep things simple: plug into, and use what your rig wants... (30 amps for your case...)
But that's just me I do this because I'm as ignorant about 'lectricity; as Hogs are about the Sabbath!


I'm bout lik u on the legtricity
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Old 09-23-2017, 05:25 PM   #4
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I'm not an expert either, but logic would tell me you just have more current available to draw from with 50amp service. Your breaker panel will only allow you to use so much. My home breaker panel is 200 amps but I'm sure what is coming from the street is much higher.
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Old 09-23-2017, 05:49 PM   #5
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I'm not an expert either, but logic would tell me you just have more current available to draw from with 50amp service. Your breaker panel will only allow you to use so much. My home breaker panel is 200 amps but I'm sure what is coming from the street is much higher.


Agreed I think that was the logic the guy who changed the plug stated. Also said the parks he covers has much less problems with the 50 amp circuits one reason is they receive less usage than the 30 amps. Stated he works on 30 amp circuits about 4 times more often than 50 amps. Just musing but thanks for your input.
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Old 09-23-2017, 05:49 PM   #6
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Technically the 30-Amp cord and motorhome wiring to the breaker panel isn't protected at 30 Amps like it should be, but in practice I'm not sure there is a significant risk since the 30-Amp breaker will limit current draw to well below 50 Amps anyway.

If for some reason the 30-Amp cord grounded, it would likely trip the 50-Amp breaker pretty fast, so distinction between 30 and 50 Amps isn't that important in my opinion.

I suppose that if a knucklehead connected their 30-Amp cord to 50-Amp at pedestal, and then used another adaptor to split power at motorhome to power 30-Amp motorhome and something else (like a second A/C or an electric skillet), then it would be possible to overload the 30-Amp cord and cause damage.

It's for that reason that the code (as I recall) requires breakers to be sized to protect what's immediately downstream -- in this case 30-Amps and not 50-Amps.

Personally, I'd stick to plugging into 30-Amp breaker unless your adaptor has a built-in 30-Amp breaker.
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Old 09-23-2017, 05:52 PM   #7
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I agree with the maintenance guy for 1 reason: The 30 Amp breaker on a lot of poles has been used and abused for years and is likely been tripped many times, making it more likely to trip under 30 Amps. Use the 50 Amp and trust your input 30 Amp breakers as a "known" entity.
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Old 09-23-2017, 05:57 PM   #8
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I have a 50 amp outlet at my home because my original coach was 50 amp . My current ( no pun intended) coach is 30 amp. I have it plugged in all the time with no problem.
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Old 09-23-2017, 06:28 PM   #9
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Not really an issue: Use either one. As mentioned above the breakers inside the coach will trip before the breakers on the pedestal. That is a good point, however, about the 30A plug getting a lot more use than the 50A one. Still, though, if the plug fits in pretty snug it is more than likely ok.

Personally we plug in the RV in the 30A plug, and the car in the 50A plug
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Old 09-25-2017, 04:59 AM   #10
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As long as your wire size is rated for the 50 amp service you can rely on your internal breakers the cord would need to be # 6 wire for the 50 amps and the 30 amp would need to be number 10 wire. Undersized wire could cause heat issues
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Old 09-25-2017, 11:07 AM   #11
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Let's be realistic about the risk...
Talking about plugging a 30A cord protected at the far end by a 30A breaker into a 50A outlet.... To have a problem, there would need to be a failure in the cord, receptacle on RV, or transfer switch that would cause it to draw more than 30A and less than 50A..
Everything else in the RV is protected by the RV's 30A breaker.
The risk should be minimal.

I would think it is quite common practice to plug in devices less than the rated circuit... Do you ever plug a 15A cord into a 20A circuit at home?
This would have less protection than what we are talking about here since there is no protection downstream of the 20A breaker.

NEC even allows multiple 15A recepticles to be on a 20A circuit... (The hard wiring must be rated for 20A, and if a SINGLE recepticles then it must be 20A. The 'pass thru' on 15A outlets is rated at 20A.). It's left to the user not to attempt to draw 20A through a single 15A recepticle.

You can decide for yourself what the risk is. Personally I wouldn't hesitate to do so.
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Old 09-25-2017, 11:50 AM   #12
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.....cut....

I would think it is quite common practice to plug in devices less than the rated circuit... Do you ever plug a 15A cord into a 20A circuit at home?
This would have less protection than what we are talking about here since there is no protection downstream of the 20A breaker.

.....cut.....
Of course it's done on a regular basis. For example, the cord on some lamps with a 60-watt bulb isn't necessarily rated at 15 or 20 Amps. Since the bulb will limit power draw to less than 1 Amp, everything should be fine.

The bigger problem (and more likely) is when a homeowner plugs a 10-Amp rated extension cord into a 15 or 20 Amp circuit and then plugs in 15 Amps worth of Christmas lights without knowing he's exceeded the rating of the cord. That can lead to fires.

On a practical basis I agree with you that the risk is minimal, with exception I mentioned above; an RV owner could split power at motorhome and thus overload 30-Amp cord. It's highly unlikely anyone would do that, but it would be similar to powering too many Christmas lights with an underrated extension cord.
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Old 09-25-2017, 12:35 PM   #13
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Originally Posted by rspicy View Post
As long as your wire size is rated for the 50 amp service you can rely on your internal breakers the cord would need to be # 6 wire for the 50 amps and the 30 amp would need to be number 10 wire. Undersized wire could cause heat issues
????

Nobody with a 30 Amp RV has a 50 Amp cord, nor is there any reason to have one, the RV will not pull more than 30 Amps for very long before it's breaker trips. Breakers/interrupts are sized so that voltage is interrupted closest to the load.
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Old 09-25-2017, 12:42 PM   #14
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That makes a lot of sense; I agree!
Why would anyone want the bulk and un-handiness of a 50 amp cord; when they can only pull 30 amps?
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Old 09-25-2017, 01:43 PM   #15
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The 50 amp plug provides two- 50 amp circuits, using a 30 amp adapter you connect to one side of the plug, insuring you will have a full 30 amps available. Again your RV is not going to draw more than 30 amps without your circuit breaker opening. Using a 30 amp circuit, the most you will have is 30 amps, less losses from old or poor connections, line loss etc.
My unit shows voltage and amp demand on the surge protector display. Most connections show the same input voltage, but I have seen as much as 5 volts higher input from 50 amp adapter compared to 30 amp connection on same box.
FWIW When the voltage is higher, the display also shows the amp draw for the same load is lower
When available I use the 50 amp adapter with 30 amp power cord..
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Old 09-25-2017, 01:49 PM   #16
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Originally Posted by Tfryman View Post
I agree with the maintenance guy for 1 reason: The 30 Amp breaker on a lot of poles has been used and abused for years and is likely been tripped many times, making it more likely to trip under 30 Amps. Use the 50 Amp and trust your input 30 Amp breakers as a "known" entity.
Right. If I am at an older, more neglected campground and the 30am breaker and female connection looks ratty, I will use the 50 amp if available with no problems.
I have used 30 amp connections where the plug got so hot you could hardly touch it due to worn out contact with the female connection.
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Old 09-25-2017, 02:09 PM   #17
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Originally Posted by Hooligan2 View Post
...
Most connections show the same input voltage, but I have seen as much as 5 volts higher input from 50 amp adapter compared to 30 amp connection on same box.
FWIW When the voltage is higher, the display also shows the amp draw for the same load is lower
...
Absolutely... The math is always Watts = Volts * Amps...
The higher the volts, the lower the amps to deliver the same watts (power).
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Old 09-26-2017, 12:16 AM   #18
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Originally Posted by JamJanTan View Post
I recently pulled into a site and the 30 amp plug had an open ground. I have a 30 amp rig. The host could not get maintenance until the next day. I checked the 50 amp and found it to be fine so plugged into 50 amp and used it. The next day the electrician? Came and changed out the 30 amp plug and problem solved. He recommended that I always use the 50 amp outlet when available. I know the main 30 amp breaker in the motorhome should protect the electronics, etc. The question to those electric minded individuals. Is it a good general practice to use the 50 amp circuit with an adapter to run my 30 amp coach? I don't have a fancy electric monitor system (on the wish list) just a cheap surge protector. Thanks in advance for your advice.
The simple answer is no. The cord will burn before the breaker will trip as the cord is only rated for 30amps....
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Old 09-26-2017, 12:28 AM   #19
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Won't the demand only be for 30 amps? So your 30amp cord should be fine.
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Old 09-26-2017, 12:31 AM   #20
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I carry an adapter, so can plug into either, since the Gemini has only a 30 amp service. Even plugged into a 50 amp service, it still all goes through a 30 amp main on the motor home, so protection is still there.
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