What is the difference between a surge protector, EMS, and EPO? Do I need one?

Dear Dave,
I am getting ready to purchase an RV. I need to know if I need the EMS, EPO and surge protector features. Progressive Industries has an EMS w/surge protection listed for $159. Hughes Watchdog Gen ll EMS, EPO, w/surge protection is listed on their website for $380. The only difference I see is the WiFi feature. From research, it appears these are the two top brands. Please help me know what to purchase. Thanks for your help. —Chris, 2018 Coach House Platinum II 241XL DT

Dear Chris,
From what info I can find on the Coach House models, the Platinum II is a Class C unit on a Mercedes chassis. Their website describes it as a “Luxury Class B+” motorhome, which frustrates me as the RVIA (RV Industry Association) does not have a B+ classification. If they purchase a chassis with a cab and frame rails called a “cutaway” chassis and build the box, it is a Class C. Whether it has a bunk over the top or not, building on a cutaway chassis is a Class C and you can tell by the bump out or “wing walls” behind the cab to the box. OK, enough on that.

It looks like the unit has a 30-amp shoreline cord going to the distribution center. It also lists a lot of what I call “glamping” features such as USB charge slots built into 120-volt outlets, wireless cell phone charging systems, 3000-watt inverter, and TVs with sound bars. Those and other items need to be protected from not only high power surge but low power, as well. So, yes, I believe you need some type of power protection device, which can be confusing.

Surge protectors

The term “surge protector” has become a generic description of the pigtail most RVers use at the pedestal to regulate voltage coming to the rig from the campground power pedestal. Most of us are familiar with the residential surge protectors or “power strips” that simply trip the breaker if there is a power surge. Most RV “surge protectors” actually protect your RV from high and low voltage, miswired pedestals, open neutral, open ground, reverse polarity, high neutral current, surges, and overheating plug/receptacles.

The difference in price comes with the amp size of 30 or 50, the features offered, and how often it can reset after a shut down. I have used both the Southwire Surge Guard and the Hughes Power Watchdog models in the basic pigtail version for years.

Some cheaper models plug into the campground source and will shut down with a surge such as a lightning strike but will not protect against high and low voltage. They will not reset and you will need to purchase a new unit.

The protection device in these are called joules, which dissipate the energy of an electrical surge. The higher the joules capacity, the more resets available, and the higher the cost.

Cheaper surge protectors do not have a display showing voltage and amp draw. I feel that is important when you have a 30-amp system as it is important to know what your energy demands are. More on this later. Also, the more expensive models will actually shut down temporarily when there is high or low voltage. They reset after 90 seconds when power is restored to an acceptable level. The Hughes Power Watchdog you are referring to has a low joules count of 3,000. However, you can replace just the surge module if you use it up. That is free for the first two years and only $39 after that.

EMS/EPO

Electrical management system (EMS) is another description that I believe has been used in generic terms, as well. Originally, an EMS was an energy management system that was installed inside the rig. It would have major 120-volt appliances connected to monitor power management. An example would be the Winnebago Powerline using the Intellitec system. If the energy draw exceeded 30 amps, the system would temporarily shut down components to protect an overload situation.

In the case of the Powerline, the first system to shut down was the refrigerator, then the rear air conditioner fan, then compressor. Typically when there is an overload situation, it is for a short time such as turning on a microwave oven or other appliance which would only create a short additional draw. Turning off the refrigerator for a couple minutes as well as the back air conditioner would not affect the performance of those units.

I noticed doing a Web search that AI Overview lists the Hughes Watchdog Gen II as an EMS (electrical management system), which I feel is a little misleading. I guess technically it could be called an EMS, as it does shut off power. However, it really doesn’t “manage” power like the Intellitec models. You will notice the Hughes website does not list the EMS description on their website, just the EPO.

Progressive Industries does list their EMS PT30X as an electrical management system. It will shut off power not only during a surge such as a lightning strike, but also if the incoming power is higher than 134-volts and lower than 104-volts. It does seem to have similar functions as the Hughes Watchdog. However, it only has 1760 Joules and does not look to have a replacement module.

How many joules will be absorbed

It is not possible to estimate how many joules will be absorbed as it depends on the amount of the surge. I believe the higher price of the Hughes Watchdog is the higher joule capacity, ability to replace the module, and the Bluetooth capabilities that allow you to see error codes from inside your rig rather than going outside to read the LED. That could be an issue during inclement weather.

I would also suggest looking at the Southwire Surge Guard model 34931, which is also Bluetooth enabled with 2450 joules. It seems to have the same functionality at a lower price than the Hughes Watchdog. You can find it on Amazon here.

 You might also enjoy these posts from Dave 

• Is there a meter to test campground outlets for amps?
• I need a 30-amp surge protector. Which do you recommend?
• Why can’t I get power through my Smart Surge Protector?
• When running roof A/C, any appliance trips 30-amp. Why?

DAVE HAS ANSWERED MORE THAN 1,000 readers’ maintenance and repair questions. Read a directory here. There is so much to learn!

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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