Huge difference between 30-amp and 50-amp hookups

Huge difference between 30-amp and 50-amp hookups

 

RV Electricity
with Mike Sokol

Dear Mike,
So just how much more power does a 50-amp shore power plug have compared to a 20- or 30-amp plug? We like to bring a lot of our electronic toys with us, and have tripped the 30-amp circuit breaker a few times. Should we consider a 50-amp plug for our next RV?  —Stan

Dear Stan,
It all comes down to watts. There are two basic numbers to consider when we want to calculate the wattage available from each style pedestal outlet: Volts and Amperes. Voltage is a measure of electrical pressure, and Amperes is a measure of available current flow. Ohm’s law tells us that Volts times Amperes equals Watts. 

• 20-amp outlet = 2,400 watts
• 30-amp outlet = 3,600 watts
• 50-amp outlet = 12,000 watts 

So here are the quick calculations:
• If you multiply 20 Amps times 120 Volts you get 2,400 Watts.
• And 30 Amps times 120 Volts equals 3,600 Watts.
• But how does 50 amps times 120 volts equal 12,000 watts and not just 6,000 watts? That’s because there are actually two separate 50-amp conductors in a “50-amp” shore power outlet. It probably should be called a 100-amp plug since that’s how much amperage is really available.

After that it’s just a matter of knowing the watts required by all of your electrical “stuff” and adding them together. All modern appliances have a tag that displays their wattage. You just add up everything you want to turn on at the same time and make sure you have enough wattage available from the shore power outlet. Since circuit breakers are only rated for 80% of their load capacity for continuous load, you need a little extra power available to make sure you don’t trip a breaker accidentally. 

Typical watt usage:
• Small Flat screen television – 50 watts
• Kids video game – 10 watts
• Laptop computer – 100 watts
• Desktop computer – 500 watts
• Hair dryer – 1,500 watts
• Toaster Over – 1,500 watts
• Small Microwave Oven – 1,200 watts
• Incandescent light bulb – 40, 60 or 100 watts
• CFL (Compact Fluorescent Light) 13 watts
• Slow Cooker – 200 to 1,500 watts (low or high heat)
• Small space heater – 600 or 1,200 watts (low or high heat)
• Overhead LED Lights – 5 watts each
• Overhead Incandescent Lights – 20 watts each
• 15,000 BTU Air Conditioner – 2,000 watts running / 3,600 watts starting surge

This is why most modern RVs have at least a 30-amp shore power plug and all large RVs have a 50-amp plug. You can see that even a single toaster oven or hair dryer would use up more than half of the power available from a 20-amp shore power outlet. But you can run a hair dryer, microwave oven, toaster oven, plus an air conditioner and a bunch of lights all at the same time from a 50-amp pedestal outlet and still have power to spare. 

So if you park your RV next to your house, you should consider having a real pedestal outlet installed by an electrician. That way you can run everything in your RV even while it’s parked in your driveway. If you only plug into your house using a dog-bone adapter to hook into a 20-amp outlet in your garage, you may not even be able to run the air conditioner in your RV. 

rv-safety-764Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com.

##RVT771

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13 thoughts on “Huge difference between 30-amp and 50-amp hookups

  1. Chuck

    So in today’s RV’S there are no 240 v appliances except a custom one like Cheap Heat

    1. Mike Sokol

      Of course there can be exceptions, but for the most part that’s correct. RVs built for North America all use 120-volt appliances, except for specialty heating products such as the Cheap Heat.

  2. LARRY MCGAUGH

    Sorry, my bad. I was only referring to US and Canada when it comes to RV’s. You are correct overseas most everything is 230 VAC @ 50 HZ. That being said we have sold quite a few of the CheapHeat systems in the Europe because the CheapHeat system will work there with no modifications.

  3. Mike Sokol

    Well, your comment about CheapHeat being the ONLY 240 appliance in an RV is not 100% correct. My articles are read in at least 60 different countries, many of which have single-pole 230 volt AC power at 50 Hz (the UK for instance). And there are a few larger Class-A RVs in the US of European origin that have 240-volt stoves, etc… But yes, for the most part, US built RVs are almost exclusively 120-volts, except for electric heaters such as the CheapHeat system.

  4. Larry McGaugh

    Even though the receptacle found in your RV is rated at 120 VAC, the 50-amp shore power is actually a 120/240 VAC four wire service. The acronym VAC stands for “Volts of Alternating Current” which means the voltage is constantly changing from 0 volts up to 120 volts Positive back down to O volts, then it goes to negative 120 volts and then back up to 0 volts. This happens sixty times a second. This is commonly referred to as 120/240 VAC 60 HZ (Hertz).
    The actual electricity that feeds your 120 VAC receptacle in your RV comes from your 120/240 VAC breaker panel. This panel is supplied with 240 VAC which is made of two 120 VAC legs that are 180 degrees out of phase. This means that when Leg-1 of the 120 VAC is going from 0 to 120 volts positive. Leg two of the 120 VAC is going from 0 to 120 volts negative.
    To get 240 VAC for the larger appliances like a CheapHeat™ system, rather that going from one hot leg to neutral (120 VAC). Power is now taken from the two opposing hot legs and since they are 180 degrees out of phase, the end result is 240 VAC. Now that the neutral (white wire) isn’t used in the 240 VAC configuration.
    Now let’s review the four wire 50-amp shore power cord, the cord we are talking about has four 6 gauge wires rated at 50-amps each. Which means the cord has two 50-amps legs at 120 VAC (Hot to Neutral) for a total of 100-amps at 120 VAC or one circuit of 240 VAC @ 50 amps (L-1 Hot to L-2 Hot), or a combination of the two.
    Wait! If we have 120 VAC @ 50 amps on the Red to White and 120 VAC @ 50 amps on the Black to White, wouldn’t that be 120 VAC @100 amps on the White wire since there is only one white wire? No it won’t, because the two hot legs are 180 degrees out of phase. When Leg-1 electrons are moving towards Positive 120 volts the Leg-2 electrons are moving towards Negative 120 Volts. This means that when correctly wired (phased) the Neutral leg will see no electron flow, that’s why it’s called the Neutral Leg, thus no overload.
    If the RV park pedestal isn’t wired correctly, and the two legs are not out of phase, you will have 100-amps applied to the white wire that is only rated for 50 amps. In that scenario you have both Leg 1 and 2 electrons moving towards 120 volts positive and then negative at the same time. Which means you have double the electron flow (Current) going through the white wire when it’s only rated for half that load. End result is an overloaded wire that will overheat and very possibly cause a fire.

    ******* DANGER ******* DANGER ******* DANGER *******

    How do you know when you have an incorrectly wired Shore Power Pedestal? There are two simple ways, one is to install a surge protector that identifies incorrect phasing and locks out the power to the RV. The second way is to use a simple voltmeter that is rated to test AC voltage up to 300 volts. If the pedestal is wired correctly when you test from Leg-1 to Leg-2 (not Neutral) and the two legs are 180 degrees out of phase as they should be, the meter will read 240 VAC. When the Shore Power Pedestal is wired incorrectly, the two legs are at the same phase. Then the test from Leg-1 to Leg-2 (not Neutral) will read 0 volts on the meter. As stated previously, this is an unsafe condition because you can have a 100 Amp load on a wire that is only rated for 50-amps. All of that being said this means that using a 30-amp to 50-amp pigtail adapter will NOT allow you to see 240 VAC in your breaker panel. Because in that scenario your just splitting the same single black hot leg on the 30 amp plug to feed both the red and black on the 50 amp plug.
    Its also important to note, that the CheapHeat™ Electric Hybrid Furnace kit is the only RV product that uses 240 VAC in an RV. It is designed to operate on a 50-amp service and it is not subject to these types of overload problems. Along with its inherent phase protection, it also has multiple high temperature safeties to protect from any overheat conditions. It is also hard wired directly into the main power system of the RV removing the potential fire hazard that can happen when plug in portable electric heaters are used.

    1. RV Staff

      For more information on the CheapHeat™ system, here’s a link to their website: http://bit.ly/CheapHeat-RVT771-comments

      Endorsed by the RV Doctor, Gary Bunzer, and recommended by RV Travel. —Diane at RVtravel.com

  5. Richard Mantz

    If your RV only has a 30amp connection and connect to a 50 amp pedestal with an adapter, are you not still limited by the converter in your RV? Seems to me you may not trip the pedestal breaker, but you still will exceed what your rv can supply if you hook up too many things.

    1. Mike Sokol

      If you have a 30-amp shore power plug on your RV, then you are limited to 30 amps total, even if you plug into a 50-amp pedestal outlet. Your RV wiring, connectors, and RV circuit breaker panel can only pass that much current without damage (overheating and catching on fire), so there’s no quick workaround. You would need to completely rewire your RV’s shore power wiring and breaker panel to utilize the amperage available from a 50 amp pedestal outlet.

  6. Tommy Molnar

    This being the case, why should I not always hook my 30amp trailer to the 50 amp plug using a plug converter? I’ve done this before when there was a problem with the 30 amp plug at my site. but considered it an emergency procedure.

    1. Mike Sokol

      Exactly right. You are limited by the design of your RV’s shore power wiring, NOT the power supplied by the pedestal.

    2. Jonathan Miller

      There is no danger hooking a 30 amp RV to a 50 amp pedestal through an adapter. Well I should say that if all circuit protections in the RV are working correctly, but it does remove a level of safety redundancy since the pedestal won’t trip until the current levels far exceed what the RV can safely handle. That being said, my 30 amp RV has been plugged into a 50 amp service for 2 years.

  7. Richard Hatheway

    Can u hookup to a 50amp shore power with a 30amp trailer with a 50amp converter plug.

    1. Mike Sokol

      You can, but since your shore power wiring and RV circuit breaker panel is only rated for 30 amps, it should trip its own 30 amp circuit breaker if you exceed that amount of current. That will protect your wiring from overheating and possibly catching on fire. So while you “can” do this, it really won’t give you any more amperage (and available wattage) than your original 30-amp pedestal outlet.

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