RV Electrical Safety: Surge Protectors vs. EMS

Apr 17th, 2011 | By | Category: RV Safety


Copyright Mike Sokol 2011 – All Rights Reserved  

This series of articles is provided as a helpful educational assist in your RV travels, and is not intended to have you circumvent an electrician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your RV or at a campground, make sure to contact a qualified, licensed electrician.

This article was prompted by an RVtravel.com reader who wrote asking if it made sense to spend $300 on a surge protector for her RV.

Surge is one of those words that have fallen into fairly common usage when in fact; it’s not very descriptive of the situation. And interestingly “surge protectors” do nothing to stop a long-term voltage “surge.”

So let’s start with a basic definition of voltage and the types of situations that can ruin your electrical gear. To gain a better understand of what we’re going to discuss, re-read my NSZ article HERE about voltage. As you will see, voltage is really electrical pressure, much like the water pressure in your pipes feeding the kitchen sink.

Electrical voltage (pressure) needs to be near a certain amount for electrical gear (like your computer) to be happy. And the voltage (pressure) we use in the USA is rated at 120 volts, give or take 5% according to the National Electrical Code. That means it could vary from a low of 114 volts to a high of 126 volts, and still be strictly within code. From a realistic standpoint though, it’s more likely to be as much as 8% low, so a 110-volt measurement is pretty common.

ELECTRICAL APPLIANCES are generally designed to run perfectly fine on anything from 105 volts to 130 volts or so. And 99.9% of the time that’s what you’re feeding them from the power line. But you can have under-voltage (brownouts) or over-voltage (broken neutral) conditions at a campground where this sustained voltage can go below 90 volts or above 150 volts. These are not voltage “surges,” so a so-called surge strip will do nothing to stop them from getting into your coach. But more on that later…

However, there are voltage “spikes” that can be induced on a power line from a variety of causes, the most dramatic one being a lighting strike near your area. That can cause a voltage “spike” of many hundreds or even thousands of volts to appear on your 120-volt wiring. Fortunately, that “spike” only lasts for a tiny fraction of a second (milliseconds) so it’s pretty easy to get rid of with a simple MOV device (Metal Oxide Varistor) built into a common “surge” strip which shorts these high-voltage spikes harmlessly to ground.

But MOV devices (which looks like a nickel with wires attached to both sides) are sacrificial elements. That is, just like a boxer in the ring, all “hits” are accumulated and they’ll eventually wear out and stop protecting your circuits from damage. Better “surge strips” have an indicator light to tell you if their MOV is still functioning or if it’s time to get a new surge strip. These MOVs are not field replaceable unless you have a soldering iron and a meter, so don’t try to fix one yourself.

The other common cause of voltage spikes are big motors being turned off, which then induces a reverse voltage spike of 10 to 100 times the nominal voltage. Again, these are short duration spikes of only a few milliseconds (1/1000 of a second) so a MOV protected “surge strip” will do a good job of shunting this voltage to ground without harm. I think the most common cause of this type of spike would be a big water pump at a campground when it switches off.

However, there’s an even bigger electrical boogieman at campgrounds that many RVers are unaware of. And that’s sustained over and under voltage conditions. This is where the voltage going into your coach from the power pedestal can dip very low (say, below 90 volts) or swing very high (180 volts or more) depending on the condition.

The low voltage condition is hard on appliances that need serious start-up current (like air conditioners) while the high-voltage condition is hard on electronics (like your computer, microwave electronics, and most everything else you plug in). And there have been instances where entire campground areas have been miswired with 208 volts instead of 120 volts. And certainly, a broken neutral connection in your 120/240-volt shore power plug can let the one side of your power dip to 60 volts while the other side rises to 180 volts with predictable disaster. In that case, the MOV in your surge strip will think that nothing is wrong and happily pass 180 volts right into your computer and microwave. Then it’s new appliance time.

TO TAKE CARE OF THIS SITUATION, companies such as Progressive Industries build an EMS (Electrical Monitoring System) device which checks the incoming voltage for correct levels and will trip a relay to disconnect your coach from the power pedestal if it goes above or below a set limit. Those same voltage-monitoring devices generally include a MOV “surge protector” which will get rid of the quick “spikes” that the relay can’t act quickly enough to disconnect.

Checking around, the $300 “surge” device you’re probably referring to is an EMS voltage monitor with disconnect relay that goes between the shore power plug and campsite pedestal. For instance the Progressive Industries EMS-PT30C has both surge protection from nearby lighting strikes and voltage protection from over and under voltage conditions as well as reversed polarity on miswired campsite pedestals and extension cords. It includes a readout that will display any power problems as well as notify you when your MOV devices need to be replaced. See here to learn more.

Progressive Industries also makes a basic surge protector for $99 that will stop the surge (voltage spike) caused by a lighting strike in the area or a water pump switching off. And it also includes monitoring lights to tell you if its own MOV circuits have been worn out by too many spikes. However, all brands of simple MOV surge protectors can’t shut off your power if the voltage swings below 90 or above 130 volts. In that case, your appliances could fry while the surge protector MOV sits there perfectly happy. Click here for more info on their surge/spike protectors.

In either event, I talked to Tom Fanelli at Progressive industries about MOV replacement in their products, and he said they would replace the worn-out MOV devices in their products for free if you paid for shipping one-way to them. They’ll then ship it back to you for free. That’s a fantastic deal!

However, both of these aforementioned devices are WAY BETTER than the $20 “surge strip” you may have your computer plugged into. These extension cord surge strips have smaller MOV devices, so they can only dissipate much smaller “surges” and often don’t have an indicator light to tell you they’re worn out. And they will do nothing to protect your inverters or built-in RV appliances.

I would get some sort of overall protector on the shore power connector. So do you spend $99 on an RV “surge protector” or $300 to $500 on a “voltage protector”? Well, that’s up to you. But considering that the cost of an RV refrigerator or microwave can be $1,000 and up, plus the cost of all the electrical things you plug in like computers, iPods, phone chargers, etc, I think the $300 to $500 of a voltage protector to be well worth the investment, and probably costs less than the deductible on your RV insurance policy.

And yes, there are a number of other manufacturers who make voltage protectors and surge protectors for RVs. But I’ve studied the Progressive Industries gear the most so I’m just more familiar with them. Perhaps I’ll review a number of Voltage and Surge Protectors in a future article.

Please send us your comments and suggestions. I would love to know how I’m doing with this important project.

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.  

18 Comments to “RV Electrical Safety: Surge Protectors vs. EMS”

  1. Kathy Cloninger says:

    Are there rubber gloves for women to wear, for protection from electrocution, while connecting to the power pedestal at the campground?

    • Mike Sokol says:

      Well, in theory if you turn OFF the pedestal circuit breaker BEFORE you PLUG-IN your shore power connector, you can’t get shocked. And if you turn OFF the pedestal breaker BEFORE you UNPLUG your shore power connector, you’re still safe. But everyone please note that if the ground pin in your campsite pedestal has been energized from a reflected hot-skin in another campsite, then the circuit breakers in your own pedestal or RV won’t disconnect you from that hot-skin condition. I think that’s a very rare circumstance, but still possible. That suggests that you should really meter the campsite pedestal plug for proper voltage BEFORE you plug in your RV, then do a quick test for hot-skin condition on your RV using a Fluke VoltAlert. This will take all of an extra two minutes under most conditions. Of course, if you’re trying to make camp in the rain that may be uncomfortable, so if you choose to skip metering the pedestal with a volt-meter, at least you can use a VoltAlert to check your RV for hot-skin as soon as your plug in and turn on the circuit breakers. That only takes 10 seconds at the most, and will probably find 99% of hot-skin conditions.

      If you would feel more comfortable wearing gloves for metering and hookup, I don’t blame you. However, electrician gloves are heavy and expensive since they’re typically rated for 600 volts or more. I feel comfortable plugging into 120/240 volts of a campsite outlet using Nytril gloves like you find at Auto Stores. And certainly, rubber dishwashing gloves will protect you from 120/240 volts as long as there’s no tears in them. However, I’m going to call one of my contacts at a company who makes real electricians gloves for confirmation of my theory.

      Mike Sokol

  2. Doug McCormick says:

    You have provided excellent information for the people, MIKE, and THANK YOU VERY MUCH.
    I’m a Retired Electrical Inspector and a Licensed Electrical Contractor. in Brighton, MI

  3. Steve says:

    Hi Mike,

    Your 12 part series was very informative. Thanks so much for sharing your expertise with a newbie like me.

  4. Mike speaks the truth! Read and re-read everything he publishes! Then pass it on to an RVing buddy! Or three…


  5. John Davis says:

    I like that you put “Surge supressor” in quotes when talking about MOV’s. because as you may know I am very fond of saying they are SPIKE suppressors, and in a real surge they become firecrackers (Well that’s what they sound like, trust me, been there, heard that).

    The article I just read featuring the 300 Dollar Progressive Dynamics.. Very good, Fully agree.

    • Mike Sokol says:


      Yup… they do go boom, don’t they??? If you want to hear something REALLY LOUD, my electricians once accidentally created an arc-flash on a 6 inch conduit’s Elle-joint when a 600-amp 480-volt cable shorted on a sharp edge. It sounded like a bomb going off in the warehouse, and a chunk of metal bigger than your fist blew out through the steel wall. Lucky for us we were a few hundred feet away on the other end of the conduit, but it impressed me a lot. This was before arc flash dangers were well known, but after that incident I took a lot of extra precautions for me and my electrical guys.

      Glad you liked the article.

  6. Steve Dziuba says:

    Mike, I’m so happy to have stumbled across No Shock Zone. I want to tell you a story that happened 35 years ago. I am a house mover by trade. I have jacked up many houses,barns, and large buildings and also moved many. My dad and I jacked up a barn for a local farmer to replace its foundation. Running near the barn was an electric fence. My Dad had a bright idea of tying a peace of wire to one of the beams then drop the other end on the fence. When the farmer would get done with chores he would always come out to visit us, resting his hand on a beam. The farmer came out just as we expected, rested his hand on the beam, then let out a yell. Dad said, what is wrong? The farmer replied, That beam just bit me! Dad said, what do you mean just bit you? The farmer said, I felt like I got bit by an electric fence. So he carefully reached out his finger to see what really happened,and got shocked again. We all laughed then explained what happened. The barn was supported on dry wooden cribbing not grounded any where, so the electric passed through the beams and continued down the fence. Later on that year we had a house jacked up putting a new foundation under it. A thunderstorm came, so we all ran under the house for cover. One of the guys rest his hand on a beam just as lighting stuck. He said, “Holly Cow”, I just got shocked. We all ran to our pick up trucks then. Ever since then we started tying a chain to a beam, letting the other end rest on the ground, in order to have some kind of ground system. Where people had to live in the house, during the reconstruction of the foundation, we would clamp a ground wire to a beam and clamp the other end to a ground rod. Now I said all that to ask you this. Now that I’m pulling my camper down the road, instead of a house, should I be concerned about grounding the frame of my fifth wheel camper once I get it all leveled up? I use wood blocks for all my supports, The camper frame reminds me of the barn 35 years ago. Not grounded anywhere. What do you think? Thanks for your response. I love how explain things out so it is easy to understand. Oh, forgive me for the mistakes I know I have made typing. I’m not good at it. But I am a good house mover. Thanks again.

    • Mike Sokol says:


      Interestingly, putting down your jacks on the ground really doesn’t “ground” your RV. Even pounding a ground rod into the earth and connecting it to your RV chassis doesn’t “ground” your RV. The only way to create an effective safety ground is to plug into a properly grounded power outlet and connect the frame of your RV to the service entrance panel’s G-N-E (Ground/Neutral/Earth) bonding point with a low-impedance path via your shore power connector, dog-bone adapter, campsite pedestal connection, and all the wiring running back to that panel. A little scary yes, but you need a continuous copper path form your RV’s frame to the service panel’s ground bonding point. The reason that a ground rod at your RV won’t work is that even an 8-fit ground rod can have a 100-ohm impedance to earth and still be considered safe. If you have a 120-volt fault to your frame and a 100-ohm path to earth, you’ll only draw 1.2 amps to earth. Which is certainly not enough current to trip a 20-amp circuit breaker, leaving your RV’s frame and skin at a full 120- volts.

      So checking your own shore power cable and all extension cord for breaks is vitally important, as is testing any campground pedestal for proper voltage, polarity, and grounding. You’ve probably seen my other articles here about how to use a Non Contact Voltage Tester (NCVT) such as a Fluke VoltAlert to check polarity as well as your RV for hot-skin voltage. And of course, NEVER accept getting a shock from an RV as a normal thing. ANY shock, no matter how small, is suspect and should be corrected immediately.

      Mike Sokol

  7. Melanie Burleson says:


    I’m a newbie with questions. I have a 2002 28ft Salem Le travel trailer plugged into a 30amp shoreline. Is there enough power to run a Roland keyboard, a Roland mc 909 workstation, a computer, and a couple of monitor speakers that are plugged into two 15 amp power strips? Or would that be too heavy of a load? Also, would i be able to run the a/c at the same time?



  8. Chris says:

    If I use an Electronic Monitoring System like Progressive, will that protect from “hot skin”? Would I still need a non contact tester to make sure?

    • Mike Sokol says:

      That will protect you from shock in 99% of the possible situations. It wont notify you or disconnect you from a RPBG (Reverse Polarity Bootleg Ground miswiring condition.

  9. Ken says:

    Hi Mike:
    I just finished reading your article in RV Travel today (10/21) and looking at EMS surge protectors. I’m comparing the Progressive Industries’ EMS-HW30c to the EMS-PT30 C or X. I like the idea of the hard wired model for two reasons. One is the security from theft and also being able to view a display from inside the RV. My shore cable is hardwired in a compartment on driver side at the rear of the 5er so I could mount the display on the inside trailer on the wall just above the compartment. What would be the advantage of the PT30X of hardwired other that being able to keep it if I buy another unit?
    By the way, there is a 30 amp female receptacle in the compartment with the shore cable. I don’t understand what it would be used for. Any ideas? Thanks Mike. I enjoy reading your articles.

  10. Jon Granger says:

    I have a 30 amp Class C motorhome. I kept my 50 amp Progressive Industries EMS . Can it be plugged into a 30 amp Park Pedestal with a dogbone connector and be able to check the pedestal’s health before plugging in the RV’s 30 amp power cord?

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