By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
I just got an RV and need to use it for COVID-19 isolation since my wife is a health care provider and she doesn’t want to come in the house after her shift. The RV is hooked up in my backyard with an extension cord and everything was working fine until she ran the air conditioner and microwave at the same time – that’s when it tripped the circuit breaker in my house. I keep resetting the breaker, but it trips again. Is there something wrong with my circuit breaker? Or is it possible the RV is drawing too much power? Should I get an electrician to fix it? I have a good electrician but I don’t even know what to ask for. —Stan
Be sure to thank your wife for her bravery and service. That’s one tough and vitally important job she’s doing, and it’s great that you’re both working to keep your family safe.
You’ve run into the weakness in nearly all RV power hookups: lack of power (watts). From your description it sounds like you have an RV power cord with a TT-30 plug. If that’s so, then you’re probably using an adapter (called a dog-bone) to plug into an Edison outlet on your house. And that’s where the trouble begins.
You see, there are three versions of shore power cords your RV would have come with: a 20-, 30- or 50-amp cord. Now, I haven’t seen a 20-amp shore power cord on an RV in decades (except for an occasional pop-up or teardrop towable), since that’s equivalent to plugging everything in your house into a single electrical outlet on the wall.
The next step up is a 30-amp shore power cord (called a TT-30 or Travel-Trailer 30), which most small and medium RVs have. It has a 3-prong plug that’s connected to an outlet that looks like this. Note that while this outlet looks like it should be wired for 240 volts, it’s most definitely only 120 volts.
Larger RVs, including most 5th wheels and coaches, have a 50-amp shore power cord that plugs into an outlet that looks like this. This is called a NEMA 14-50 receptacle, and it’s wired exactly like any 50-amp 120/240-volt stove outlet in your home.
Let’s explore just how much power (watts) is available from each one of these outlets:
- A 20-amp service can supply 2,400 watts
- A 30-amp service can supply 3,600 watts
- A 50-amp 120/240 service can supply 12,000 watts (6,000 watts per 120-volt leg)
Now let’s look at a chart of how much wattage a typical appliance in your RV draws:
- Microwave = 1,000 watts
- Computer = 200 watts
- Television = 200 watts
- Air conditioner = 1,300 watt (running)
- Electric water heater = 1,500 watts
- Battery converter/charger = 500 watts
So if your RV is plugged into a 20-amp outlet at home using an adapter like this one, then the first chart shows you that there’s 2,400 watts you can use. But a microwave will draw around 1,000 watts when it’s running and the air conditioner will draw at least 1,300 watts when the compressor is running (much more for a second or two of startup current). Add in addition to that you may have a television set on drawing 200 watts, maybe your computer is pulling another 200 watts, and your RV has a converter to make 12 volts DC for the interior lighting that’s likely pulling at least 200 and maybe 500 watts. Add that up in nearly any combination and you’ll quickly get above the 2,400 watts of power you can get from your house.
If this is the case (and I’m pretty sure it is), then you need to consider having your electrician run a dedicated 30-amp power outlet on the exterior of your house near where your RV is parked. That will give you 3,600 watts of power instead of the 2,400 watts you’re getting from an Edison outlet. Your wife will still have to do a little power management since 3,600 watts of power isn’t enough to run everything in your RV at once. So I would suggest she not run the microwave while the air conditioner is on, and make sure your water heater is set to propane, not electric.
One really important thing to tell your electrician is that the 30-amp outlet for your RV is wired for 120 volts, NOT 240 volts like a similar-looking dryer outlet in your house. See my diagram comparing the two types of outlets.
If the electrician accidentally wires the 30-amp outlet with 240 volts and you plug your RV into it, you’ll probably burn up most of your RV’s electrical system in a few seconds. So show your electrician my chart and make sure you double-check the voltage before plugging your RV in for the first time.
Good luck and stay safe. And tell your wife she’s a hero to us all.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s stay sane and play safe out there….
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.
Mike’s the man! Love the photo’s.
When I had my original TT30 installed, the electrician had reversed the hot/neutral. Good thing that before plugging in I used a dogbone to be able to plug my 3-light w/voltage circuit tester.
In fact, I always do this when plugging into an ‘unknown’ power post.
I treat electricity like firearms. Always assume it is ‘loaded’ (miswired) because it can make you just as dead.
Thank you for an easy to follow article.
Mike, I have seen that you have posted this info a number of times, but new people keep coming back with the same questions. I don’ t know how it could be done, but a permanent posting somewhere that “a 30 amp plug is not a 30 amp plug – for RVs” could save some people a lot of grief.
That’s why I’m working on creating a library of my articles on RVelectricity.com. But this will take hundreds of hours to compile and cross reference the thousand or so articles I’ve already written for the RV industry. It’s a lot of work to do in addition to writing several new articles every week.
Thanks so much for posting this Mike, great info that I’m going to print out and save in my book. Much appreciated.
Thru the years, this daily news letter has been such a technical class for me.
Thank you to all who jump right in and ask questions and certainly thanks to those who possess the technical knowledge to provide answers.
What a gift.
Now where’s my credit card to make another ‘fitting installment’ to help keep this daily coming forth?
(One of these times I’m gonna bite the bullet and travel to an rv gathering to hear Mike teach. )
We just this week lost one of the very great teachers. Ah Gary how we’re gonna miss you dear soul.
Darn dust in this room…… Can’t see a thing all of a sudden.
Thanks, Austin. And darn — now you got me crying again. 🙁 —Diane at RVtravel.com
Hello: One other thing. Also don’t forget that each time the circuit breaker kicks that it kicked because it got very hot and weakened the spring that did what it supposed to and kicked the breaker off. After 3 or 4 or 5 times, and it will take less heat to kick it again. You will need to replace the circuit breaker.
As usual Mike gives top notch professional advice. Stan below also gives excellent trouble shooting advice. I’ll give you some amateur advice that basically is Stans advice in amateur terms.
Of course don’t use more than one big draw Appliance at a time. Assuming you’re doing that and the Breaker still trips.
Of course turn all power off to the House and test to make sure the power is off before you mess with any wiring!
Is the House plug you’re using a GFI, and that’s what’s tripping now? If so, I have had several of those GFIs’ go bad. Replace it with a new one but make sure you get the bigger Amp capacity. Those GFIs’ seem to have a life span and sometimes don’t want to be reset.
If it’s the actual House Circuit Breaker tripping in the House Panel, I have also had those go “bad”. Like Stan says swap that Breaker with one of the other similar rated Breakers in the Panel and see if that fixes it. They may be hard to get out but they are like big plugs. If it is a bad or “weak” House Breaker, depending the Panels’ age, you may or may not be able to find another Breaker to replace it with.
If any of this freaks you out, bite the Financial bullet and call the Electrician . Just tell him/her what you told us.
Good luck and I pray for your family’s good health.
First, I’d like to add my thanks and gratitude to your wife and you for supporting her.
Next, I had a similar situation with power. An electrician added a dedicated 30 amp power outlet [I had room to add in my electrical panel]. Added benefit – added guest quarters.
Thanks for clear information. I appreciated the info on adding the dedicated 30 amp outlet when parked by house as that matches my circumstances. To think, in my ignorance I may have had the wrong 30 outlet put in😱. Again- thanks.
It would be forward thinking to run a 50 amp power line (with a 50 amp circuit breaker) inside the home. That way if/when an upgraded (from 30 amp to 50 amp) RV is purchased , only the exterior outlet will need to be replaced.
Good idea, if his panel is able to accommodate an added 50-amp circuit.. No need to replace the 30-amp outlet with a 50-amp, just use a 50-amp dog bone to connect to the TT-30 30-amp trailer
Stan, of course Mike is technically correct. I didn’t understand from your letter if it now trips every time you plug in (even with air and microwave off), or only when two power hungry appliances are used at the same time in the RV.
If only tripping when item like microwave and air conditioner (or iron, or blow dryer) are run at the same time, TURN OFF air conditioner when you are going to run microwave.
If tripping all the time, then try a different outlet, on a different circuit. If it no longer trips when just running air, then replace the back yard outlet or circuit breaker (depending on which is causing the fault). You can swap the breakers in the panel to isolate if it is the breaker’s fault.
The tripping could depend on what is being used on the circuit inside the house. If you plugged RV into a circuit that is shared with the laundry room, for example, and you plug in your iron inside while the RV is running air or microwave, then breaker will pop. Ditto for washer. Ideally your back yard plug isn’t shared with anything inside the house and ideally your back yard receptacle is on a dedicated 20 amp breaker. And, ideally that back yard receptacle isn’t a finicky GFI (ground fault interrupter) receptacle.
For immediate relief, try troubleshooting when it happens (what all is running inside and outside on that circuit). Make sure you are plugged into a 20 amp circuit, not a 15 amp circuit.
After troubleshooting, make sure you have a thick enough cord running from RV to house. That would be a 12/3 cord or even better, a 10/3 cord. These cords are available at hardware stores, local home depot/lowes and the like. 10/3 will cost twice as much as a 12/3. 12/3 is the minimum to be used.
Yes, wiring a dedicated 30 amp circuit is ideal. If you are doing that, make sure you have a cord that supports the 30 amps the entire length from your RV to your new circuit. That cord will have a different type of 10/3 connector (RV connector). You’ll probably have to order online, or go to an RV store.
Excellent point about what also may share that ‘backyard’ outlet. Many newer homes, in order for electrical contractor to save a few bucks, will add an outdoor outlet to an EXISTING bathroom or garage (any place that requires GFCI outlet). This is fine for low current draw outdoor use. I agree, ideally the ‘backyard’ outlet used by OP would be dedicated 20 amp outlet. I had a screen room built with electric and electrician tapped off the the garage GFCI outlets, There were spaces in electrical panel for its own circuit.
Mike, thanks for a well-written, easy to understand explanation. Your illustrations were excellent, and make things perfectly clear. I enjoy your articles and learn something new in many of them. Much appreciated.
Yes, fully understandable!