Thursday, June 1, 2023


Surge protector for 30- or 50-amp outlets


Hi Mike,
First off, I just bought your book on Amazon and have read 80% of it, as well as bought all the tools for testing electrical pedestals off Amazon. I love your water pressure to electrical comparison! My wife and I are going to RV full time starting next month in a Class C. Before I bought your book, I was planning on buying a Progressive Industries surge protector, the 50-amp model.

Your book explains that 50-amp and 30-amp pedestals are more than just a difference in plugs. If I buy this surge protector for 50 amp, and then come to a campsite that is 30 amp only, can I use an adapter to plug the 50-amp surge protector to the 30-amp outlet? Am I setting myself up for a big problem? I ideally don’t want to buy both a 30-amp and a 50-amp surge protector, but I really don’t want to have an issue either. 

Thank you for your time, and again thanks for the book! —Doug

Hey Doug,
Thanks for your kind words. As far as teaching electricity by comparing it to water, that’s exactly how I taught myself all about voltage, current and resistance so many years ago. I came across a really old book in the library (remember those things?) about electricity when I was perhaps 10 years old, and it used water pressure and flow to explain how voltage and current worked. So a few experiments with a garden hose in the driveway got me interested in all things electrical. But back to the future (or is it the present?).

You’ve made a great choice by planning to purchase an Electrical Monitoring System (EMS) type surge protector since it will continuously test the voltage at the pedestal and shut down power to your RV if the pedestal voltage goes too high or too low, or loses the safety ground. Now, it’s not monitoring the current flow (amperage) since that’s the job of the circuit breakers in the pedestal, to watch for too much current. So the EMS unit is only concerned with monitoring the line voltages. And since the voltages on a 30-amp and 50-amp power outlet are really the same on both legs, it just won’t care if your RV is plugged into a 50-amp/240-volt outlet, or a 30-amp/120-volt outlet.

What that means is that the 50-amp surge protector you’re planning to purchase will operate perfectly on either a 50-amp or 30-amp pedestal outlet, as long as you use the appropriate dogbone adapter. In your case something like this will do the trick. You just plug the 30-amp side of the dogbone adapter into the 30-amp pedestal outlet, and the 50-amp surge protector into the 50-amp side of the dogbone adapter, and your 50-amp Shore Power Plug on the RV goes into the EMS surge protector.  

The job of this dogbone adapter is to take the single 120-volt leg of a 30-amp pedestal outlet and jump it to both of the 120-volt legs in the 50-amp shore power plug of your RV. And that’s what feeds both legs of the 50-amp EMS surge protector whenever you’re plugged into a 30-amp pedestal. So no matter if you’re plugged into a 30- or 50-amp outlet, the EMS will correctly monitor the shore power for high or low voltage as well as a lost ground. Which is exactly what it’s supposed to do.

Let’s play safe out there….

Mike Sokol

Be sure to sign up for Mike’s new monthy newsletter about RV electricity. First issue this fall. Sign up here.

Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit for more electrical safety tips. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.




0 0 votes
Article Rating
Inline Feedbacks
View all comments
5 years ago

I have a question for you regarding the amperage on my 5th wheel. Originally it had a washer/dryer hookup with a 50 amp receptacle for the dryer. The trailer does NOT have an air conditioner. How difficult would it be to convert the electrical system from the 50 amp service to a 30 amp service? I know a 30 amp cable is a lot lighter than a 50 amp cable so I am looking to see if I can save some weight due to not having to carry the heavier cable among other things that are not needed.

Richard Davidson
5 years ago

Something else to think about with the type of surge protector shown is the “STEALability of the Protector. Lets face it, not everyone in an RV is honest and laying they’re hands on a costly RV surge protector is a prize! Be sure your surge protector cannot be just un plugged and taken. I opted for the permanently installed kind and not the plugin type.

Mike Sokol
5 years ago

I tend to recommend the permanently installed surge protectors for exactly that reason.

Mike Sokol
5 years ago

Always remember that a surge protector is not a circuit breaker. It can’t limit the amount of current that passes through it. A surge protector can only clamp voltage spikes from things like nearby lightning strikes and water pump motor generated back EMF. It is the job of the circuit breakers in the Pedestal to limit the amount of current draw by your RV to 50, 30 or 20 amperes, depending on which outlet you’re plugged into and how heavy your shore power wiring is.

J Hamme
5 years ago

Reverse polarity may not hurt normal electrical appliances but it can fry electronics. Some inverter converters have sacrificial diodes which fry the charging circuits if reverse polarity. I have a 1000 dollar repair bill to prove it. Contact Tripp lite for more info. My new progressive surge protector does pick up reverse polarity but if it does not shut down for that error I still have exposure if current passes. I check before hook up but in unlikely situation it occurred later it’s a problem. Comments?

Mike Sokol
5 years ago
Reply to  J Hamme

I’m not sure you’re correct about reversed polarity destroying your Tripp Lite unit. What model number do you have? I’m going to contact Tripp Lite tech support and get a schematic of its circuitry. In a previous life I was a pretty good circuit designer, so it will be interesting to learn exactly what they’re doing inside the box and if reversed polarity can indeed damage it. And if they’ll send me a unit to test, I’ll set it up with reversed polarity and see how it responds. No modern electronics should be damaged by a simple neutral-hot swap.

J hamme
5 years ago
Reply to  Mike Sokol

Getting ready to travel so will respond with specifics when i get on road but it definitely ruined the charging circuitry. The inverter part was working fine but I could not charge the batteries thru the generator or plugged in. I found several articles discussing the impact on sensitive electronic with reversed polarity.issues. I had to prove my case to the state park that had the issue. The inverter/converter was 9 years old . It was hard wired and I think 600watts. I don’t remember exactly what wires were wrong but the 20amp plug was fine so not voltage interested in what you find out. Thanks for the response.

Mike Sokol
5 years ago
Reply to  J hamme

If you’re referring to a reversed polarity on the DC side of the inverter, then yes that will destroy electronics in seconds. But a pedestal can only reverse the 120-volt AC polarity. Again, I’m not sure that any modern electronics can be harmed by a swapped hot-neutral. But I can see if there was some aftermarket diode clamping circuitry added (by the dealer or RV builder?) that strange things could happen on the AC side. I’ll need the exact model number of the inverter and maybe a photo of how it was hooked up. Email anything to

Mike Sokol
5 years ago

Not really, according to code. While it certainly would work, that situation would make it possible to draw more current through your 30 amp wiring than it’s rated for, and thus the possibility of a fire. Going the other way is fine since a 30-amp outlet can only supply 30 amperes of current into wiring that’s rated for 50 amps. So overheating of the conductors isn’t possible that way.
I know there are all sorts of dogbone adapters that allow you to plug your 30-amp shore power cable into a 50 amp pedestal outlet, but that’s also a code violation and could cause a fire if you overload your 30-amp cable with 50-amps of current. So I can’t recommend that sort of hookup.

5 years ago

Am I understanding that you could take a 50 amp surge protector and plug a 30 amp RV into the 50 amp receptacle with the dogbones and be safe?

Gene Bjerke
5 years ago

Not so much a comment as a question (I don’t know how else to contact you). I have a 30-amp TRC surge protector that analyzes the pedestal before passing on current. Recently, I plugged in and the unit reported a Reverse Polarity condition, but it passed the current through anyway. Since I didn’t have many other options (this was not in a campground) I plugged into the motorhome and continued as usual. As it happened, I didn’t need to use any 110V appliances other than a CPAP. Everything seemed normal.

What is the danger, if any, to using a power pedestal that has reverse polarity?

Mike Sokol
5 years ago
Reply to  Gene Bjerke

By itself, a reversed polarity outlet is not dangerous. It won’t cause a hot-skin condition by itself, and all appliances should operate normally. However, if there was a secondary Ground-Neutral bond in your RV (definitely a code violation itself), then you would either trip the main circuit breaker, or create a hot-skin voltage on your RV. Plus, if anyone was working on an electrical appliance inside of your RV while plugged in, and they assume that the white/neutral wiring isn’t energized, then they could be at risk of shock or electrocution. Plus, it’s the basic details that hint at the overall condition of the wiring in a facility. If they can’t even get something simple like the hot-neutral polarity wired correctly, what even more important details have they missed?

Mike Sokol
5 years ago

I’m proposing a yearly inspection of all campground pedestals for exactly that reason. Pedestal power outlets take a real beating, which can cause lost grounds and neutrals as well as overheated connections that can melt and catch fire. Proper maintenance is the only way to guarantee everyone’s safety.

Chuck Dunn
5 years ago

Something else to think about the 50 to 30 (and reverse) is the 30 amp connection in parks are used more and a lot of time by renters and newbys who have not learned what they are doing. That means the 30 amp receptacle may really be beat up or even broken or chipped. With the dogbone you can use the 50 amp side which will most of the time be in a lot better shape. Have phun.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.