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  1. #1
    Rolling Along
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    50 amp.... Why so big?

    I've done some fairly extensive mods to my house on wheels and along the way I've wondered about how we got to 50 amp shore power. That question comes back up every time I drag out the huge heavy power cord to plug in. Why do we carry that beast around?

    First, let's compare 30 and 50 amp service in terms of power. With 30 amp service, there is theoretically 3600 watts available and with 50 amp service there is 12000 watts available. How is it that almost overnight, the RV industry decided that we need more than three times the power to run the house. 12 kw is a lot of power! In my rig, 2 AC's, microwaveable coffee maker add up to less than 8 kw. And that's assuming no soft starts and all appliances start at the same time!

    Yes, it's nice to have pretty much unlimited power available, but how much do we really need? And how much weight are we willing to carry to support that habit? Personally, my back and shoulders can't handle wrestling the 50 pound power cord in and out of its home, so I don't.

    I haven't found my ideal setup yet, but most of the time I use a 10 gauge power cord that weighs about a quarter of what the beast weighs.

    It seems to me, a little bit of thought in the industry would go a long way toward making things simpler and lighter.

    Just my Sunday morning ramblings... I hope you enjoyed.
    Roger, Stacy and the Sophie the fur kid

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  2. #2
    Site Team Ynot4me2's Avatar
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    I could be way out, but don't you actually have 2 x 25amp at 120v? Which would be 2 x 3000w. 6000w total
    Steph & Lise
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  3. #3
    Rolling Along
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    Quote Originally Posted by Ynot4me2 View Post
    I could be way out, but don't you actually have 2 x 25amp at 120v? Which would be 2 x 3000w. 6000w total
    The 30 amp RV plug is 120 volts. That's 3600 watts. The 50 amp is at 240 volts. That's where the huge increase comes from.

  4. #4
    Big Traveler boyscout's Avatar
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    Quote Originally Posted by Roll With The Changes View Post
    The 30 amp RV plug is 120 volts. That's 3600 watts. The 50 amp is at 240 volts. That's where the huge increase comes from.
    This is often debated; hoping this doesn't spark another debate.

    Our 50-amp power is not 240V, it is two legs of 120V at 50 amps per leg and is called "120/240 VAC split phase". The wiring of the park supply (hopefully), the heavy supply cord that you don't like, and the distribution of the power in the trailer are all configured to supply two legs of 120V power at 50 amps per leg. Without modification, you can't get 240V anywhere in the trailer. If you can, something is misconfigured and chances are high that the neutral is seeing about double the current that it is rated for, which will let smoke out somewhere in the circuits.

    One CAN measure 240V off the incoming supply by measuring across the two hot legs, but nothing in the trailer uses the two hot legs together. Each hot leg is wired with the neutral, not the other hot leg. Measuring either hot leg to neutral - which is what everything in the trailer sees - will show 120V.

    This 120/240 wiring configuration is different from 240V outlets typically required for clothing dryers and welders, for example, which require a true 240V supply.

    Your observation that the 120/240V system can deliver 12,000 watts is correct, just not all on one circuit/leg. Your "2 AC's, microwaveable coffee maker" are not usually all running on the same leg for that reason - if they were you'd likely hear a 'click' from the circuit breaker panel.

    EDIT: @xrated beat me to the punch above while I was whittling at this post.
    Mark - 2018 Solitude 310GK - 2017 F-350 diesel SRW short box - Pullrite Superglide hitch

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    New Member
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    Quote Originally Posted by Roll With The Changes View Post
    The 30 amp RV plug is 120 volts. That's 3600 watts. The 50 amp is at 240 volts. That's where the huge increase comes from.
    The 50 Amp is not 240 V. Never plug your RV in to 240 V. It's all 120 V.

  6. #6
    Site Sponsor Jerryr's Avatar
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    Quote Originally Posted by dsasay View Post
    The 50 Amp is not 240 V. Never plug your RV in to 240 V. It's all 120 V.

    OK, PLEASE READ XRATED’S POST #10 IN THIS THREAD FOR A VERY CLEAR EXPLANATION ABOUT 50A RV SUPPLY VOLTAGE.

    An RV 50 amp plug is connected to a NEMA 14-50R receptacle. The same receptacle that I plug my 50 amp 240v electric car into. In fact it’s the exact same receptacle that my house 240v electric stove is plugged into. That plug supplies 240 volts to my Electric car charger and to my house electric stove heating elements between L1 and L2.

    An RV separates L1 and L2 in the RV power distribution box into 2 separate 120 v legs, each capable of 50 amps each. If you measure between L1 and L2 at the receptacle you WILL measure 240 volts. If you measure between L1 and neutral or between L2 and neutral you will measure 120 v each.

    Now a 30 amp RV TT-30R receptacle IS ONLY 120v with a single hot leg, a neutral and a ground. Occasionally an uninformed installer will unwittingly wire that as a 240v with 2 hot legs instead of 120v with a single hot leg.


    Here’s a diagram of a 14-50R. Notice that there is 240v between the X and Y terminal.

    Last edited by Jerryr; 04-19-2021 at 12:27 PM. Reason: Corrected NEMA typo
    Jerry & Linda
    Emma & Abby our Mini Golden Doodles & JR our Amazon Parrot
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  7. #7
    Site Team xrated's Avatar
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    Quote Originally Posted by Jerryr View Post
    OK, PLEASE READ XRATED’S POST #10 IN THIS THREAD FOR A VERY CLEAR EXPLANATION ABOUT 50A RV SUPPLY VOLTAGE.

    An RV 50 amp plug is connected to a NENA 14-50R receptacle. The same receptacle that I plug my 50 amp 240v electric car into. In fact it’s the exact same receptacle that my house 240v electric stove is plugged into. That plug supplies 240 volts to my Electric car charger and to my house electric stove heating elements between L1 and L2.

    An RV separates L1 and L2 in the RV power distribution box into 2 separate 120 v legs, each capable of 50 amps each. If you measure between L1 and L2 at the receptacle you WILL measure 240 volts. If you measure between L1 and neutral or between L2 and neutral you will measure 120 v each.

    Now a 30 amp RV TT-30R receptacle IS ONLY 120v with a single hot leg, a neutral and a ground. Occasionally an uninformed installer will unwittingly wire that as a 240v with 2 hot legs instead of 120v with a single hot leg.


    Here’s a diagram of a 14-50R. Notice that there is 240v between the X and Y terminal.

    Exactly correct Jerry. Sometimes it's a hard concept for folks to understand, but it's factual, accurate, and exactly the way a 50amp RV plug configuration is wired. Thank you for the picture that helps to show the plug configuration.
    2016 F350 CrewCab Dually
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  8. #8
    Site Sponsor Jerryr's Avatar
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    After installing my MORryde tall power cord reel in my replection 5th wheel I no longer fret handling the 50 amp cord. It’s not cheap but it is a well built quality product that makes handling the cord way easier.

    At home I actually plug into our 30@/240v 4-wire dryer outlet with an adaptor for the 50:amp RV plug. I can run both AC units and the converter but I watch current used when using the microwave or electric water heater.

    At our cabin in addition to a dedicated 50a RV outlet on the side of the cabin I also have a 14-50R outlet with a 40 amp breaker that I primarily use for my electric car in the shed. I have plugged the RV into it on occasion and can run everything without coming close to the breaker limit.
    Jerry & Linda
    Emma & Abby our Mini Golden Doodles & JR our Amazon Parrot
    2017 Reflection 337RLS, Build Date 01/2017, Titan Disk Brakes, Goodyear G614s 235/85/16 G Rated tires
    2022 F-450 King Ranch Ultimate, 4,868 lb Payload, Bedrug Bedliner, Andersen Ultimate II Aluminum 5th wheel hitch
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  9. #9
    Rolling Along OurNewEra's Avatar
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    From personal experience the last campsite we were at we had 30 amp. We tripped the breaker with water heater, A/C, and microwave. If I have shore power I would rather have 50 amp so I don't have to think about what I can run. If I want to think about the electric and what I can run I'll go boon docking.

    So 50 amp is a very nice convenience
    Mike & Lisa
    Central Florida
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    Rolling Along RV Sailor's Avatar
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    Talking

    Quote Originally Posted by Jerryr View Post
    After installing my MORryde tall power cord reel in my replection 5th wheel I no longer fret handling the 50 amp cord. It’s not cheap but it is a well built quality product that makes handling the cord way easier.

    At home I actually plug into our 30@/240v 4-wire dryer outlet with an adaptor for the 50:amp RV plug. I can run both AC units and the converter but I watch current used when using the microwave or electric water heater.

    At our cabin in addition to a dedicated 50a RV outlet on the side of the cabin I also have a 14-50R outlet with a 40 amp breaker that I primarily use for my electric car in the shed. I have plugged the RV into it on occasion and can run everything without coming close to the breaker limit.
    Off topic
    See you have an African parrot and a dog. I had that combo once but had to give the parrot a new home. I caught that very smart bird terrorizing our 90 lb German Shorthair Pointer Thor by “ yelling commands at him when we weren’t in the room with them. Grown dog ....heard Thor SIT, LAYDOWN.......BAD DOG in my voice . One day. Quennie had to go and I thought I would need a dog psychiatrist for the hound
    Donna and Dave
    Annapolis, Maryland
    2021 Grand Design Imagine 2500RL / Dodge Ram Longhorn 2500 6.4 Hemi
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