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Old 03-20-2023, 02:46 PM   #1
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Need 50 AMP service clarification

I am trying to mentally understand how a 50 AMP RV electrical circuit works. Does the RV plug in box have two 50 amp 120v inputs, or are there 2-25 amp inputs (1 from each main input lead) that could be combined into a single 50 amp 240v line if needed. Either way, each line leaving the RV plugin box is carrying either 25 amp service, or each line has 50 amp service. Which is it?
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Old 03-20-2023, 02:49 PM   #2
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50A Service

This should help
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Old 03-20-2023, 03:01 PM   #3
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Quote:
Originally Posted by PNGento View Post
I am trying to mentally understand how a 50 AMP RV electrical circuit works. Does the RV plug in box have two 50 amp 120v inputs, or are there 2-25 amp inputs (1 from each main input lead) that could be combined into a single 50 amp 240v line if needed. Either way, each line leaving the RV plugin box is carrying either 25 amp service, or each line has 50 amp service. Which is it?
The service is 50 amps per leg for a total of 6,000 watts per leg or 12,000 watts total power to the RV. It can be more easily thought of as 100 amp total service with 50 per side.
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Old 03-20-2023, 05:00 PM   #4
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What RVs call 50 amp service is 50 amp 120/240 volt service, just like your electric range.

You have 2, 120 volt legs using a shared neutral. Because of the shared neutral, it's not 2 , 50 amp 120 volt inputs.
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Old 03-20-2023, 05:24 PM   #5
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Dual 50A Circuit Breakers
Each 50A CB feeds a 120VAC line.....L1 & L2

Read up on it here
https://www.myrv.us/electric/
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Old 03-20-2023, 05:27 PM   #6
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Originally Posted by twinboat View Post
What RVs call 50 amp service is 50 amp 120/240 volt service, just like your electric range.

You have 2, 120 volt legs using a shared neutral. Because of the shared neutral, it's not 2 , 50 amp 120 volt inputs.
Yes, No, sort of, maybe.... Sorry had to ...
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Old 03-20-2023, 05:27 PM   #7
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In almost all cases there are two 50 Amp feeds, called L1 and L2, from the AC pedestal that are 180 degrees out of phase with each other so that if you measured from one hot socket to the other hot socket on the 50 Amp NEMA socket you would read 230 to 240 VAC.

However, almost all RV onboard generators output only 1 phase of 120 Volts AC and that is connected to both L1 and L2 in the transfer switch when on generator power.

The usual power box with circuit breakers used in RVs does not have any breaker spaces that can accomodate a 240 Volt circuit like a home breaker box does, which is fine since the generator does not generate 240 Volts anyway.

Generally when on shore power you have 50 amps available for loads fed by breakers on the L1 or A side of the power box and another 50 amps available for loads fed by breakers on the L2 or B side. The generator used does not make that much power available, for example a 7,500 watt generator will make a total of about 60 available to both sides.
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Old 03-20-2023, 05:38 PM   #8
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Originally Posted by powercat_ras View Post
In almost all cases there are two 50 Amp feeds, called L1 and L2, from the AC pedestal that are 180 degrees out of phase with each other so that if you measured from one hot socket to the other hot socket on the 50 Amp NEMA socket you would read 230 to 240 VAC.

Let's change the " In most cases" TO "this is how it is wired in 100% of the cases if properly wired"!


Read 240 VAC between the two hots-- properly wired.


Read 0 VAC between the two hots-- incorrectly wired.
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Old 03-20-2023, 05:43 PM   #9
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Let's change the " In most cases" TO "this is how it is wired in 100% of the cases if properly wired!


Read 240 VAC between the two hots-- properly wired.


Read 0 VAC between the two hots-- incorrectly wired.
YEP^^^^

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Old 03-20-2023, 05:44 PM   #10
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Same as your house 240. But line 1 and line 2 never combine to make 240 in all but some of the newer very high end Rvs. 240x50 is 12000 or if you prefer 120x50+120x50 is 12000 watts
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Old 03-20-2023, 05:48 PM   #11
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Originally Posted by PNGento View Post
I am trying to mentally understand how a 50 AMP RV electrical circuit works. Does the RV plug in box have two 50 amp 120v inputs, or are there 2-25 amp inputs (1 from each main input lead) that could be combined into a single 50 amp 240v line if needed. Either way, each line leaving the RV plugin box is carrying either 25 amp service, or each line has 50 amp service. Which is it?
The way a 50 amp RV is wired is two 50 amp hot lines with a shared neutral. Understand they are using alternating current. AC changes direction 60 times a second. The hot lines are "phased" so to speak. Meaning when power is going in one direction on one line it is going in the other direction on the other. Realize this happens 60 times per second. If you are drawing the exact same amps on each line you will find 0 amps flowing on the neutral because the same thing is happing on the neutral, and they counteract each other. So yes. You can use 100 amps total if balanced.

If somehow a 50 amp outlet is improperly wired and both 50 amp lines were in the same phase, in other words, the power going the same direction at the same time on both lines you would need a neutral capable of handling 100 amps. This would also be the case if you wanted to try and get 240 volts out of the 2 50 amp 120 lines on an RV circuit. You would need a neutral that could handle whatever the total current you were trying to draw from both lines. This is why some type of protection device is a must-have. If somehow one hot line and the neutral get switched big problems.

When you plug into a 30 amp at a place that has only that, you do not get 2 30 amp lines. There is only one hot 30 amp and one neutral and one ground. You get only 30 amps total because the adapter you use to go from a 30 amp outlet to a 50 amp plug just connects the on 30 amp hot line to both 50 amp lines to the distribution center in your RV.

I spend a lot of time in Mexico and all the sites have only 30 amps. I am currently plugged into two outlets with 30 amp cords and an adapter that allows me to connect two 30 amp outlets to my 50 amp plug. So I have 60 amps. I made sure the two outlets were "phased". If I measure across the hots on each cord I get 240 volts but each 30 amp line is 120 and only feeds one 120v line to each side of my distribution panel.

If I had to switch to a different outlet on the other side of my site that one is not in phase, and both 120 v hots are on the same side of the 240v circuit. I could theoretically be putting 60 amps through the neutral. But I wouldn't do it.

The only exception to this I have seen is we had a guy in the park here that was from Germany. 240 is the standard. He built himself an RV out of a 1972 Mercedes bus. Had it shipped to Philidelphia and flew over. In Europe they use 240, in the Americas, it's 120. They traveled all over Europe at first, then have traveled almost as far south as you can go in South America. The guy must be an electrical genius because he has figured out a way to make it work on both systems. Some kind of transformer and switching between Europe and the Americas
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Old 03-20-2023, 05:56 PM   #12
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This would also be the case if you wanted to try and get 240 volts out of the 2 50 amp 120 lines on an RV circuit. You would need a neutral that could handle whatever the total current you were trying to draw from both lines. This is why some type of protection device is a must-have. If somehow one hot line and the neutral get switched big problems.

The way this is worded it’s wrong. You have ordinary house 240 to your coach. If you built the coach to use 240 everything would work just fine. The neutral carrys only the difference in amps being drawn on L1andL2. So a 50 amp neutral is all that is required.
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Old 03-20-2023, 07:51 PM   #13
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This would also be the case if you wanted to try and get 240 volts out of the 2 50 amp 120 lines on an RV circuit. You would need a neutral that could handle whatever the total current you were trying to draw from both lines. This is why some type of protection device is a must-have. If somehow one hot line and the neutral get switched big problems.

The way this is worded itís wrong. You have ordinary house 240 to your coach. If you built the coach to use 240 everything would work just fine. The neutral carrys only the difference in amps being drawn on L1andL2. So a 50 amp neutral is all that is required.
This absolutely.

A 240V load doesn't use the neutral so it's not even needed. In household wiring you'll sometimes see a small neutral wire going to a large 240 load like a range, but it's there because the control electronics run on 120V and it only carries the current for the 120 load.
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Old 03-20-2023, 08:24 PM   #14
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[QUOTE=powercat_ras;6451360]
However, almost all RV onboard generators output only 1 phase of 120 Volts AC and that is connected to both L1 and L2 in the transfer switch when on generator power.

FYI Onan 10K and 12.5K generators put out 240V power. I have mine set up to power my home, in the event of a power outage. With 160 Gallon of Diesel, very handy.
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