Thursday, December 1, 2022


RVelectricity – Surge protectors: basic vs. advanced


By Mike Sokol

Dear Mike,
I’m really confused about which type of surge protector to purchase for my RV. There are lots of smaller, inexpensive ones for under $100 that look pretty nice, but I see a bunch of larger ones called EMS protectors that are supposed to keep your voltage steady. Is that all true? So what exactly do you get for your extra $200 or $300 if you choose the EMS version over the cheap ones? —Peggy Sue

Dear Peggy Sue,
You’re in luck, because I’ve just streamed an RVelectricity webinar last Thursday morning that covers all of your question in 9 minutes. And I don’t just talk about it, I show you how these different classes of surge protectors work with my custom variable-voltage desktop pedestal.

Of course, you can’t buy a piece of test gear like this. First you have to want one very badly (check); second, you need to have the engineering chops to put it together (double check); and finally, you need a reason to build something like this because it’s completely useless for any practical purpose other than testing things like surge protectors (triple check).

To understand what these surge protectors do, first we have to classify the various power problems you can have at a campground, or even at home. Now, this is not every possible power problem, but I can show the most common and dangerous one here.

Voltage surge or spike: This is a very short duration transient voltage (commonly called surge, which is why they’re called “surge” protectors) that can reach 2,000 volts or more. This creates cumulative damage to your electronics such as the television set, converter/charger, microwave, furnace, electric blankets, etc. This is the simplest power problem to resolve since MOV (Metal Oxide Varistor) devices have been around for decades and are an affordable solution that manufacturers build into every “surge” strip.

Low-voltage: Contrary to internet lore, low campground voltage does not automatically cause your RV to draw more amperage from the pedestal, except for one big item – your air conditioner compressor. However, any resistive components in your RV (hair dryer, electric space heaters, electric water heater, etc.) will draw less current as the voltage goes down. Anything below 110 volts is getting iffy, and below 105 volts is considered to be dangerous for rooftop air conditioners and residential refrigerators. If it gets down to 100 volts or below – fugetabout even plugging into it.

High-voltage: This usually happens when there’s a loose neutral in a split-phase 120/240-volt service, either at the pedestal or even in your 50-amp shore power line somewhere. It can damage anything with electronics, so say goodbye to the extensive circuit boards in your 3-way refrigerator, air conditioner, microwave and furnace. Ouch!

Open-ground: This can occur at the campground pedestal due to poor connections, or even inside of your RV for the same reason. While it’s usually not dangerous to your RV’s electrical system or appliances, it can be very dangerous to you and your family since that’s what allows a hot-skin contact voltage to occur. If you ever feel a shock from your RV, unplug it immediately and have its grounding checked by a qualified technician.

Reverse-polarity: Here’s another urban myth that needs to be dispelled. In an RV shore power connection, reverse-polarity refers to the hot and neutral being swapped. So now the neutral is at 120 volts and the hot is at 0 volts. If all other wiring is correct then this should not be immediately dangerous, but it does tell you that whoever wired that pedestal or outlet didn’t know how to test it. Plus, this condition is very dangerous for any technician working inside of a live panel on your RV since the white wire now is energized with 120 volts, while they were assuming it was at 0 volts. Been there, done that!

Open-neutral: Well, on a 30-amp 120-volt shore power connection this should be obvious since nothing will be working. But on a 50-amp 240/120-volt split-phase service (yes, that’s what it’s called), the neutral is what divides the one phase of 240 volts into two poles of 120/120 volts. If the neutral fails, then the 240 volts can divide however it wants to, so 180 volts on one hot leg and 60 volts on the other hot leg can easily occur. And yes, the 180-volt leg will probably be connected to the expensive things like your refrigerator, microwave and anything else with circuit boards that can burn up.

Now that you know the basics, watch my video below which explains what type of surge protector can mitigate which electrical problems.

Here’s the webinar I just streamed Wednesday night and posted last Thursday morning. Click on the video to watch me vary the voltage up and down to see how these two different types of surge protectors respond. And no, I won’t build you one of these pedestal variable voltage demonstrators, but wait until you see the cool new outlet test demo I’m building for myself. I create any possible miswiring condition in just a few seconds. And it uses rotary switches from a Soviet-era missile launcher. Yes, it really does.

Let’s 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



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Greg Walters
2 years ago

I just wanted to add a couple thoughts to this discussion. We have 2003 Fleetwood Excursion 39P.
We did a lot of upgrades because we felt the bones were really good. We were right, but knew there were alot of worn-out parts. With regard to the Surge Protection. First I replace the ends on all the cables 50 and 30. This proved the right move. Many of the cables were dark almost a foot back. Second I installed a hardwired 50 amp surge protector so I didn’t have to mess with it and constantly unplug it.
Quick story as to it’s worth went to a state park in Michigan UP Indian Lake. We plugged in to 50 and the protector would not connect. Tried once more, nope. Plugged in to empty lot next door and snap, no problems. Called the park. They came and checked with plug in one and no problem. So I plugged in and there’s the problem. So they took off the cover and the normally white neutral went from white to black. ah ha So when you’re upset that it won’t turn on it may not be your fault.

Gary Swope
2 years ago

Thanks, Mike. That video was very informative. I think the total protection unit is very cheap insurance for a persons RV.

Retired UPSer
2 years ago

Thanks Mike. I have been shopping for a surge protector and I must admit I wanted to buy the cheapest protection until I saw your video. Now I realize that my RV is worth an investment in better protection.

Steve S.
2 years ago

Good Morning Mike! This video was wonderful. Several months ago I was asking a question in your FB page about the cycling on/off due to over/under voltages and concerns about damage to equipment due to this cycling. I left the group due to the number of abusive responses and I never did get an answer to this question. Thanks for answering most of my questions. The question that remains is, aside from any electrical devices in my rig that have motors, are there any other devices that will be significantly affected adversely due to an undervoltage? Thanks!

Mike Sokol
2 years ago
Reply to  Steve S.

Steve, we’ve been working hard to limit the abusive answers on FB, but it seems to be the nature of the beast. And your answer about low voltage is that while things like your microwave won’t likely be damaged by low voltage, they’ll just take longer to cook. Space heaters will put out less watts, and most computers have universal switching power supplies that are good for any power from 90 to 250 volts. Modern battery converter/chargers should also operate just fine down to 100 volts or so. That sounds like an interesting experiment for me to do. I just need to add a big 30-amp Variac to my test bench.

Steve S.
2 years ago
Reply to  Mike Sokol

Good Afternoon Mike! That’s pretty much what I thought. Over the summer I was at a state campground with severe undervoltage and the EMS kept cycling. I turned off the AC and disconnected the EMS and plugged in my simple surge protector until the evening when voltages went back up. This was an older campground, and only had 30 amp service, which is fine for me as my rig is 30 amp. I was wondering, generally speaking, would a campground with 50 amp service tend to be less likely to have undervoltages since they need to support the higher usage? Thanks.

2 years ago

So, when we spend tens of thousands, or even hundreds of thousands on these RV toys, why dont the manufacturers add such equipment to the unit when it is being built. A simple solution would be something built into the RV that clicks off when it senses an issue in the shore power. A big plus would be that it tells you in plain language what it found, instead of the usual assortment of colored lights that make you go look for one of the multiple “operation manuals” that came with your new toy. It’s the same reason we get Dometic Pathetic and Nevercold refrigerators, water heaters buried behind the plumbing, inaccessible batteries, universal locker keys, and on and on.

2 years ago
Reply to  Dan

…designed by isolated drawing board staff, managed by accountants, built by people who are on the clock churning them out, over-hyped by marketeers who set expectations very high.

2 years ago
Reply to  Dan

“Why don’t the manufacturers add such equipment to the unit when it is being built?”

$400 more Dollars in build cost for no visual results the customer will easily see.

It’s as simple as that!

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