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RVelectricity: Why does electrical adapter trip the circuit breaker?

Dear Readers,
This question comes up time and time again: “Why does my 50-amp RV trip the 30-amp circuit breaker when I need to use a dogbone adapter to power it from a 30-amp pedestal?”

Here’s what I previously published:

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 at 120 volts is actually 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 some loads like air conditioners and refrigerator compressors can have an inrush current up to several times their running amperage, you’ll need a little extra amperage left over.

Typical watt usage:

• Small flat screen television – 50 watts
• Kids’ video game – 10 watts
• Laptop computer – 50 to 100 watts
• Desktop computer – 200 to 400 watts
• Hair dryer – 1,500 to 1,800 watts
• Toaster oven – 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 to 1,500 watts (low or high heat)
• Overhead LED Lights – 5 watts each
• Overhead incandescent lights – 20 watts each
• 15,000 BTU air conditioner – 1,800 watts running / 3,600 watts starting inrush current


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It’s all about the plugs…

This is why all modern RVs have at least a 30-amp shore power plug and most large RVs have a 50-amp plug. You can see that even a single toaster oven or hair dryer can use up to half of the power available from a 30-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.

How to connect a 50-amp RV to a 30-amp outlet

You’ll need something called a 30 to 50 amp dogbone adapter. It will not give you more power (you’ll still have only 3,600 watts or a total of 30 amps at 120 volts), but a properly wired dogbone adapter will route the single leg of power from the 30-amp outlet to both legs of the 50-amp shore power cord feeding your RV.

So, if you park your RV next to your house, you should consider having a actual 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 dogbone 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.

Let’s play safe out there….

Send your questions to me at my RVelectricity forum here.

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

##RVT1067

 

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Bob M
1 month ago

Another thing we may not realize is just because you have 50 amp power to your RV. Don’t mean the RV manufacture balanced your receptacles in your RV. Not thinking I was making coffee and at the same time outside. I was letting my Blackstone elect griddle heat up. It kicked the RV’s circuit breaker which also had the fridge on the same circuit. I was surprised the Fridge was on the same circuit. When I 1st bought the travel trailer I asked for the elect schematic and Jayco wouldn’t give it to me because it was under warranty. When the circuit breaker kick on your RV. Push it down than push it up to reset.

Thomas D
1 month ago

No one mentions the 80% rule. A 30 amp curcuit give you 24 amps. If you have a continuous load. ( i think code says it’s a half hour or more. Things heat up and breakers trip. .and outlets burn up and make things trip faster.

Mike Sokol
1 month ago
Reply to  Thomas D

The 80% circuit breaker rule only applies to continuous loads over 3 hours in length, not to typical RV loads. And all connectors are rated for 100% of their rated capacity forever. Of course, this depends on perfect conductor termination and non-oxidized contacts.