Wednesday, February 1, 2023


RV Electricity: Surge protector types

By Mike Sokol

Dear Mike,
I have a 2019 Winnebago Minnie Winnie Plus. Is an 825 joules surge protector sufficient protection for this trailer? Many surge protectors are not UL certified. Is it necessary to have a UL certification? Thanks. —Tony Carestia

Dear Tony,
That’s a start, but what you really need is an EMS/Surge Protector with a relay that will disconnect your RV from too high or too low voltage, or when the chassis develops a hot-skin voltage. A simple surge protector can’t do all that. It will only protect you from nearby lightning strikes.

Here are the differences between a simple/basic surge protector and an advanced/EMS (Electrical Management System) surge protector.

The basic surge protector (which you can purchase for around $75 to $125) that you have is essentially a bigger version of the surge power strip you might have for your computer. Its job … it’s ONLY job … is to stop voltage spikes from passing through itself and into your delicate/fragile electronics. It does this with a device called a MOV, for Metal Oxide Varistor. The basic RV surge protector just has a bunch of MOV devices inside of it, and the job of MOV is to short out any high-voltage spikes to the shore power ground BEFORE they can enter into your RV.

But the MOV device is a sacrificial element. That is, every time they take a voltage spike hit, the MOV loses a little of itself in the process. And after hundreds of voltage spike “hits,” the MOV has died and is no longer able to protect your RV from these so-called “surges.” That’s why you’ll often find a little light on a quality surge protector that lets you know if the MOVs are still functioning.

Now to go just a little deeper, the Joules you see are the total amount of energy hits the surge protector can absorb before the MOVs are dead. And each Joules is equivalent to 1 watt of power for 1 second of time. So the more Joules your surge protector is rated for, the more (and larger) electrical spikes (surges) it can absorb before the MOVs are dead, and you need to repair the surge protector or replace it. So a surge protector with a higher Joule rating simply has more MOV devices, each of which can absorb up to 350 Joules of voltage spikes (surges) before it dies.

But that’s only the story of the basic (inexpensive) surge protector.

The more advanced EMS (Electrical Management System) surge protectors include a large relay and onboard computer that can disconnect your RV from the shore power line automatically if the voltage gets too high (above 128 volts), too low (below 104 volts), lost its ground connection (causing a hot-skin condition), the generator has gone off frequency (running too fast or too slow for a non-inverter genny), or even if you’ve lost the neutral wire connection of the 50-amp service down inside of your RV (called downstream open-neutral protection).

However, all these extra features come at a price (around $300 or thereabouts), so expect to pay about three times the cost of a basic surge protector for an EMS version.

So which one do you need? Campgrounds don’t seem to spend much money or effort maintaining their shore power pedestals, so many of them are in bad shape. And even 10 years ago campgrounds didn’t seem to have as many electrical problems as they do now, likely because RVs are drawing more and more power all the time.

For example, I see a lot of RVs now with clothes washers and dryers, dishwashers, electric fireplaces and huge home entertainment systems. All of these things take power, lots of it, and campgrounds just weren’t designed for that much electrical load. So that’s why we often have brownouts, blackouts and burned up shore power cordsets.

That’s why I think that EVERYONE should have some sort of EMS surge protector – simply because it only takes a few seconds of over-voltage to burn out all sorts of expensive gadgets in your RV, including your microwave, refrigerator, inverter, converter and anything else.

What can we do about the general problem of poor maintenance of campground pedestals and your shore power connections? Well, you’re in luck because my next RVelectricity newsletter, which is publishing on Sunday (tomorrow), will cover troubleshooting and maintenance of shore power connections. Not signed up for my RVelectricity newsletter yet? You can register for it (and other newsletters) HERE.

See you there!!!

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

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2 years ago

Thank you for the info….may I please ask which EMS surge protector you recommend? Thank you!

3 years ago

You have some good info, but didn’t answer the actual question.

Tim Miller
3 years ago

Will a 50A EMS (Electrical Management System) surge protector work with a 30A system if that is all that is available at a campsite? My motorhome has a 50A system.

3 years ago

How do you secure that expensive EMS Surge protection? Some time ago a fellow RVer said someone stole his while he was away from the campsite.

3 years ago
Reply to  Mike Sokol

I think I’m going to go with the hard-wired version. It sounds like less problems with weather as well as theft. We’ve camped in some real wet sloppy campgrounds in Alaska. Water and mud can be a major problem with extra hardware hanging on the pedestal especially if you have to use an adapter to drop from 50 to 30amps.

3 years ago
Reply to  PeteD

Not 100% fool proof but my unit has a metal tab and I run a bicycle cable lock thru it and around the power supply post. If they are serious, they can cut it out I would guess but it keeps the honest person a bit more honest.

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