By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
Dear Mike,
So how do I decide what kind of surge protector goes where? I sort of understand the difference between the $100 (basic) protectors and the $300 (advanced/EMS) surge protectors, and I also see some generator transfer switches advertised that include surge protection and voltage monitoring. What are the basics? And can I run a cheap protector plugged in the pedestal (in case it gets stolen) and the expensive surge protector installed in my RV? Will the two of them interfere with each other? —Penny W.
Dear Penny,
Great questions, so let’s start with the definitions of basic and advanced/EMS surge protectors.
A basic surge protector (like this Progressive Industries SSP-50X) primarily does one thing – it protects against voltage surges (what us EE guys call spikes). The ability to absorb these voltage spikes is due to MOV devices, which are rated in Joules (watt-seconds of power). In general the higher the Joule rating of a surge protector, the bigger and more voltage surge/spikes it can protect your RV from. These surge/spikes come from things like nearby lightning strikes and big pump motors at the campgrounds starting and stopping.
Some of the basic surge protectors also include LED lights to let you know if the pedestal outlet has reversed polarity or an open ground, but they can’t do anything to disconnect your RV from an improperly wired pedestal. Nor will they turn off the power to your RV if the pedestal goes down to 104 volts or above 130 volts (and even higher). As you can imagine, voltage that’s too low or too high can damage your RV’s appliances like the converter, air conditioner, microwave, and all the other expensive bits.
An advanced surge protector is also 
called an EMS, which stands for Electrical Monitoring System, and it not only includes the MOV devices with Joule ratings of how much and how many voltage surges/spikes it can protect you from, it has a big relay that can disconnect your RV from other incorrect wiring and voltage conditions such as too-high voltage, too-low voltage, open ground, open neutral, and reverse polarity.
But the ability to detect and disconnect your RV from these power problems comes at a cost in both size and money. So a Surge/EMS Protector is much larger, and typically costs 3 times as much as the Surge-Only versions. So expect to pay $300 or so for an EMS/Advanced surge protector from Progressive, Surge Guard, Camco or Hughes.
Next, there are indeed generator transfer switches available that include Surge-Only protection, as well as advanced versions with full Surge/EMS protection and the ability to monitor and disconnect your RV from power when something goes wrong.
Finally, I believe it’s a great idea to include a basic portable Surge-Only protector at the pedestal since that would take the initial hit of any lightning strike or other voltage spike/surge problem. But you should also consider a hard-wired Surge/EMS protector inside of your RV which could be built into your generator transfer switch, or be installed as a stand-alone box with a remote monitor inside of your RV.
A combination of two surge protectors (Surge/Only Portable at the pedestal and a Surge/EMS inside of your RV) will not interfere with each other, and will basically double your Joules of surge and spike voltage protection. And the inexpensive (under $100) portable Surge/Only protector on the pedestal becomes the sacrificial element that can be destroyed by a really big lightning hit in the area, or stolen by a thief looking to liberate you from your more expensive Surge/EMS protector.
To read more about how MOV devices in Surge Protectors work, read one of my previous articles on the technology HERE.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
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 Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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Great information, Mike! I have wondered the same thing. I am glad to know that in this case of surge protection that you can never have to much!
Thanks for all your great articles and for your concern for the health and well being of RV’rs everywhere. I have a question I dont know if you can answer or not. We are taking our 1967 VW camper to the UK and Europe. We are having a horrible time finding information as far as paper work etc and have been concentrating on that. Then yesterday it occurred to us “Electrical hook ups to the bus.” Currently we use 110 with an inverter. We have been planning on taking our own appliances, We do not use a microwave but occasionally a hot plate. No curling irons or blow dryers either. We do not have a refrig in there yet nor do we have heat we use a small electric heater in US. We are in the process of re doing the interior and we do plan on bringing back to US
I think it’s worth mentioning that besides the advanced ems’s, Hughes Autoformers have surge protection as well. The biggest problem in most parks is low voltage- which the Autoformer was designed to deal with. If I had it to do over (or if my current unit fails) I’ll likely get one.
Good article, Thanks