Tuesday, September 26, 2023


Why you need an intelligent surge protector

I’ve written a number of articles here about surge protectors and the difference between intelligent and basic models. The overview is that basic surge protectors usually cost less than $100 and offer protection from nearby lightning strikes and voltage spikes on the incoming power line. However, they can’t protect your RV from an over-voltage condition that occurs if you happen to connect your 30-amp shore power plug into a pedestal outlet that’s miswired with 240 volts instead of 120 volts, as is clearly labeled on the front of the outlet. When that happens it can destroy much of your RV’s expensive electrical system in seconds.

On the other hand, an “intelligent” surge protector from Progressive Industries or Surge Guard will indeed disconnect your RV from an over-voltage pedestal before damage occurs. But brains don’t come cheap, with the price of a 30-amp intelligent surge protector costing around $300, and a 50-amp version costing as much as $500. So is that much of an investment really worth it? Does this kind of miswiring condition happen routinely or just once in a blue moon?

With that question in mind I ran a survey last week in my RV Electricity Newsletter asking how many of you had encountered a 30-amp/120-volt pedestal outlet miswired with 240 volts. Both editor Chuck Woodbury and I were astounded to discover that 10% of you had indeed found one in the wild. See the survey below, which is still active and will accept your vote.

What does this all mean? Well, I would have guessed maybe 1% of our readers would have encountered a miswired 30-amp pedestal, but it appears to be pretty common. And you know from reading my articles about voltage that many of the electrical systems in your RV will be destroyed in seconds from this kind of abuse.

So what can you do to protect your investment? Well, I know you don’t like to spend money, but in this case I think it’s the wisest thing you can do. Here are two examples of 30-amp intelligent surge protectors on Amazon that I’ve personally tested, and either should do a great job of protecting your RV from static over-voltage conditions as well as any voltage spikes. Progressive / Surge Guard  and here’s the latest Surge Guard model which isn’t available on Amazon just yet.

Who’s to blame for this miswiring epidemic? Well, I don’t think it’s any single party. Certainly the NEMA TT-30 outlet form factor has to take some of the blame since it so closely resembles an old 30-amp/240-volt dryer outlet. (Click the picture on the right for a full-size image.) And the electricians or technicians who install them incorrectly should take some of the blame since the outlets are marked quite plainly for 125 volts. But in the final analysis, you the RV owner must take at least some responsibility for making sure whatever you plug into is within electrical specs. Until there’s some nationwide test-and-tag program for all campground and home pedestals with a bonded/insurance rider that will pay for any RV damage from over-voltage, it’s still up to you to be the final authority on verifying voltage before plugging in. 

So until you get your own smart surge protector, it’s good to brush up on testing your pedestal with a digital meter before plugging in. I’m getting ready to produce a bunch of new Electric Videos on this and other electrical topics in a few weeks, but for now here’s a video on pedestal testing I published a few years ago.

Let’s play safe out there….


Mike 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. For more info on Mike’s qualifications as an electrical expert, click here.




  1. Is there some reason why the Progressive Industries EMS-PT30X that you recommended NOT UL certified? I just purchased one and was surprised that it did NOT carry this certification!

    • There’s many electrical products that are very high quality, but not UL Listed. Many manufacturers consider UL Listing to be an extra $10,000 they have to spend that really doesn’t do anything for them. I’ve not only visited the PI factory a few years ago, I have a pair of their 30 and 50-amp units torn apart on my bench right now for evaluation, and I can tell you they’re built extremely well. But that’s an interesting question that I’ll ask their engineering department next week.

  2. Hi Mike, I recently purchased a fifth wheel and also at your advice a 50 amp Progressive EMS for “cheap insurance”. I read Ed Day’s question on 50 amp to 30 amp which prompted me to ask this question. If I have only a 30 amp service available can I use a “dog-bone” adapter (30 to 50) and then connect my 50 amp EMS to check out the pedestal’s electrical status. Will the EMS provide me with the protection I need prior to hook up and while hooked up?

  3. Any preference on hardwired surge protector or one use at pedistal ? Getting new 5th wheel & wondering what you would use. Thanks Larry

  4. Mike I’v looked But could find answer to this. We’re getting a new 5th wheel 50 amp , my ? Is should I get a hardwired surge protector or one that plugs in at pedistal . What little I know is that your ground wire should be as short as possible. A hardwired unit would be using the whole length of my power cord. I’v read that some use both, that sounds a bit of overkill. What are your thoughts? Thanks Larry

    • There’s really no difference in operation from the ground wire being a few feet longer. It all comes down to personal preference. I have readers who prefer the flexibility of a portable unit, and they can transfer it to another RV easily. However, it’s also easy to steal, so many of the proponents of hard-wired unit since it’s bolted down insider of the RV. If you have a small RV you may not have room for a hard-wired unit and you may need to stick with a portable. But if you’ve got a 5th wheel RV I assume there’s plenty of room for a hardwired unit if that’s what you choose. I personally like the hard-wired versions with the remote readout inside the RV. It’s one less thing to mess with, and I don’t have to chain a portable unit to the pedestal so it doesn’t walk away.

  5. Hello Mike!
    I just had an unusual, but potentially damaging experience: my 30 amp Cord was knocked partially out of the receptical by a worker. I came back to find my inverter panel reading an Over Voltage and red light, and my RV had switched over to batteries all day, running them down as the refrigerator was set to A/C.
    What I found was the Cord was “half” connected, I think the neutral wire was disconnected, and possibly the ground as well.. but the hot leg was still making contact! Fortunately, all the protection devices you have recommended worked, no damage found.. yet!
    Thank you so much for your well written articles.. you have saved me from serious damage many times now!

  6. I love my Progressive 30 amp unit. After all the years I have read this Newsletter I would never plug into any campground without using it.
    I have encountered at least 3 times where there was a problem and had to move to another site. I bought the unit with all the options and feel so safe with it. I also use a chain and lock on it to the post because I want to keep it.

    • Great that you’re protected. I get emails every week from readers who didn’t bother with a surge protector, and they paid the price with a damaged RV.

  7. Hello – I have a tiny little Scotty which needs to plug in to a 30 amp outlet. If I go to a campground that only has 50 amp outlets, will that fry my electrical system? This is probably basic 101 but I am new to rv camping. Only had tents in the past. Thanks for going back to basics.

    • No, this will work perfectly. Remember, the 50-amp pedestal outlet has 50 amps of current available on each of 2 legs, and if your RV only needs 30 amps, then it will take only 30 amps of current. And your 50-amp to 30-amp dogbone adapter should only connect you to one of the 50-amp outlet legs, ignoring the second leg. Since each leg is 120-volts, then your RV will see only 120-volts and all will be well. However, I do recommend you get a smart surge protector that will monitor these voltages since it’s still possible for something to go wrong in the campground power that could over-voltage your RV’s electrical system and cause a lot of damage. It’s cheap insurance.

  8. this isn’t a comment it is a question, we bought a Saber 5th wheel with a Hisense fridge in it & it only runs on 120 volts at 1.7amps I would like to know what the start up amps are & if it would be ok to run this on a generator & what size I would need. Also there is an inverter in the trailer & I would like to know approximately how long the fridge would run on a 12 volt deep cell battery. I know there is a lot of variables with the battery but just a guess. I can’t find a web sight for the fridge or I would ask them. any help would appreciated

    • Dave, you need to do some homework before I can even hazard a guess. Here’s the Hisense website which should give you a start. https://www.hisense-usa.com/appliances/refrigerators-freezers but I would guess the startup current on the refrigerator to be at least 3 times the nameplate current draw. So perhaps 5 to 6 amps on startup for maybe 1 second or less. I’m sure that would all easily run from a Honda 2000is generator, but you’ll probably want to run other devices at the same time. You need to do an assay of everything that needs electricity and how much of it you want to run from the generator. Then we can do a better guess.

      You also need to find out what size and number of storage batteries you have. Remember that since you’re converting 12 volts on the battery side to 120 volts on the AC side, you’ll also have a 10:1 change in current. That means that the 6 amps of startup current on the 120 volt side will multiply by a factor of 10 up to 60 amps from the battery, but for only a second. But without battery capacity there’s no way to make an educated guess on how long this will run.

      Gather some more info and I’ll try to help.

  9. Question? I have a 50 AMP to 30 AMP short extension cord for times when I pull into a spot with only a 50 AMP receptacle. So far I haven’t run into problems. Does this mean the 50 AMP Receptacle is only 120 Volt or that my extension cord/adapter is only picking up one leg of the 220 Volt 50 AMP receptacle?

    • It does mean that your 50 amp to 30 amp adapter is picking on only one leg of the 50-amp outlet. You still have to be careful not to overload your 30-amp shore power cord since there’s now a 50 amp circuit breaker feeding it. In theory you should have a 30-amp breaker in your RV’s power panel to limit the current, but I’ve seen enough strange wiring in RVs that almost anything is possible. If your 30-amp cord is getting hot, then something is wrong….

  10. We had an electrical emergency two years ago at an RV park at Diamond Lake in OR (near Crater Lake). We were a group of 5 rigs traveling together. There was an electrical “event” (surge?) at the main power box for our loop of the park. Three of the rigs in our group suffered extensive damage to microwave ovens, A/C units, inverters, compressors, etc. One friends’ RV was completely filled with smoke and ash. The bummer was that it was the first stop of an extended trip and they had to set up repair appointments along the the way to get things fixed.
    One of the gals in our group had the presence of mind to go to the office at the RV park and ask for the name of the park’s insurance company and the phone number of the agent. Also, the RV park was very helpful in collecting all the contact information from each of the RV owners who suffered damage. As far as I know, they were all reimbursed for their repair costs after submitting copies of their repair receipts.

    • Sounds like the neutral opened up on the feeder going to that section of the campground. That will allow the voltage to swing around wildly, going up to 240 volts depending on the load balance, but more like 180 to 200 volts is typical for this type of failure. This is another example of why you need a smart surge protector for your RV. Even though the voltage might measure correctly when you first connect to shore power, it can change in a heartbeat and take out your RV’s electrical systems in seconds. I should do a few videos of appliances being destroyed by 240 volts. I’m sure my kids would help me find donor appliances to destroy.

  11. My travel trailer has a WFCO 8735 Power Converter. Reading the WFCO specs on the unit, it states “ALL MODELS: Standard Safety Features/Protections: Over Current, Over Temperature, Over Voltage, Reverse Polarity.”
    So do I need a separateSurge Protector too?

    • From a quick peek at the WFCO 8735 manual , it looks like it will protect itself from over-voltage, but it’s a converter, not an inline smart surge protector, so it can’t disconnect any of your other 120-volt systems or appliances from 240-volts. If you’ll have your dealer contact me I’ll be glad to gather more info on this product. So I’m guessing that you do want an additional smart surge protector as well.

      • Thanks Mike – I was thinking the same thing. My dealer couldn’t confirm either way! I’ll buy a smart surge protector anyway – I’m kind of a “belt and suspenders” type of guy anyway!

        • It’s really sad that many RV dealers aren’t more knowledgeable about the products they sell. For example, I get tons of questions from readers about hooking up portable generators to RVs. And this is after they’ve exhausted all info that both the generator and RV dealers can supply. I’ve offered to do training seminars at some of the larger RV dealers to educate their staff about electrical hookups, but so far there’s been no traction.

          • I imagine that’s because it does NOT so far effect the sales. Also happy to service a hook up gone bad. Sad…. Maybe I will be surprised by highly ethical and caring individuals.
            I have not picked up my RV yet.. This is all very interesting. As a single lady w/ beastly dog as co pilot , I would be disapointed to be upside down out of the gate.

  12. Progressive also offers a lifetime warranty on their EMS products; if there is a product failure (this does not include damage from an electical surge, or from the pedestal) they’ll replace it free of charge. Everyone should have one, it’s easy for me to justify the cost when I added up the $$ it would cost me to replace all of the electrical components in my RV. It would be in the thousands…

    • Yes, from what I’ve seen Progressive does offer an outstanding warranty on their products. And you not only have to factor in out of pocket expenses if your RV’s electrical system is fried. You can lose an entire vacation season which is difficult to explain to the grandchildren ready for an adventure.

  13. Hi MIke: This week I had to put the third new surge protector in my 2014 Winnebago. The coach came with a SurgeGuard built in unit. The first one failed 18 months after we picked up the new coach—parked in a 5 star rv resort. We heard a loud bang and electrical smoke filled up the compartment. The second one failed this week by burning up with smoke filling up the coach. Almost caught on fire with wire insulation burnt 6 inches up and the parts inside the SurgeGuard melted. Is this an inherently defective product? Any ideas?

    • Follow up: I received an email from Winnebago and they said to make sure the wires going into the Surge Guard were properly torqued down. That was an interesting reply since the first unit was factory installed during the build and the second was installed by a Winnebago service center. I have not heard back from SouthWire, the manufacturer of the SurgeGuard.

  14. We are a mobile rv service company. We have come across 30 amp mis-wired outlets twice in the last couple of weeks. With the number of people buying new rigs, they are now getting 30 amp power put in at there house. Here is the problem, most electricians will maybe never or very seldom install a 30 amp box, and when the see it they think no problem it looks like a dryer outlet so they install it the same way. Be sure that the person you hire knows the difference. Also if need be have a RV tech check there work before you plug in.

    • Yes, I’ve noticed an uptick in emails about this problem as well. Even though the TT-30 outlet is clearly marked for 125 volts I’ve had a number of “electricians” argue with me that it needs to be 240 volts. One of my buddies who camps around the new England area has seen several miswired 30-amp outlets in the last two years. He ALWAYS tests voltage before plugging in. I’m now really suspicious of any new receptacles since electricians don’t seem to be paying attention to what the outlet and CODE clearly states for TT-30 receptacle wiring.

    • Yes it can. The 30-amp outlet is virtually identical to a home-style 20-amp/120-volt outlet except it has more amperage available to power your RV. I’ll throw that in my list of videos to do. Plus Chuck and I are experimenting with live streaming some of our seminars. But if you want to see this up close and personal make sure to attend one of my seminars in Elkhart. I’ll have a bunch of cool demonstrations to show you, including my Flor Fina cigar box with a bunch of Soviet era rotary switches from a rocket launcher I built to demonstrate outlet failure modes. And no, I am NOT making this up….

  15. I had my charger inverter damaged by reverse polarity. Then too late I got a progressive device. I think it is important to note that the higher cost devices do more than surge control and they are usually labeled EMS devices. Mine is next to highest level, check 9 codes and covers reverse polarity and under voltage as well as surge or overvoltage along with other things. The undervoltage brown out can damage computers etc. The most expensive EMS actually regulates voltage vs shuts off but I decided did not need that. I paid about 240 on amazon . The other nice feature is a 2min 16 second delay before it transfers power to the rv. This gives it plenty of time to test errors first and you or it can shut off power before any damage.with this device I no longer feel the need to unplug during bad elec. Storms too. So worth it. I encounter reverse polarity a couple times a year.

    • J hamm, this is not the first time I’ve heard that a charger-inverter was damaged by reversed polarity. But from an EE design standpoint I don’t see how that can occur. If you’ll send me info on the make and model of your charger-inverter that was damaged, I’ll follow up with the manufacturer to see if I can learn how this happens. My background in failure analysis hints that something must be wrong with their circuit design for this to occur. But maybe I’m missing something.

      • It was the 600 Warr charger inverter by Tripp lite installed in a roadtrek. The reversed polarity damages the “sacraficial diodes. The inverter kept working but I could not charge the battery thru shore power or generater.only way to charge was by running engine or charging battery with battery charger or solar. I believe it was the plug in version.it was replaced with the newer 750 watt charger inverter.thanks.

  16. Hi Mike:

    As a rule I usually Plug in my Smart Surge Protector, then power on the pedestal and watch the codes. I have a progressive 50 Amp protector. It runs its cycle and then shows any Error codes that may exist. I usually get E0, meaning the power coming out is correct! I then power down and plug in my power cord and then turn the breakers back on, knowing that the power box is good to go.

    I am always concerned at some RV parks where the Power Pedestals are OLD and really Worn looking! Depending on the Campground, I will usually bring to the Parks attention that they should consider replacing some of these boxes with new ones.

    • Yes, old pedestals with worn outlets can be dangerous. I’ve suggested to the industry that there’s some sort of yearly or even semi-yearly test and tag system where all pedestal outlets are checked for proper voltage, grounding and wear. But until there’s a way to pay for it and legislation to make it happen, you’re all on your own as far as verifying the power before plugging in.

  17. Mike, I have a hard wired progressive ind 50 amp smart surge protector. About 10% of the time I plug in, I get a high freq alarm and shutdown. It usually shows 60 hz. Then it resets itself automatically and is fine, just showing the PE7 error. Any thoughts?


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