Is a surge suppressor or EMS system really needed for your RV? My recommendation is YES.

What is a power surge anyway, and why is it so damaging? According to the NEMA (National Electrical Manufacturer's Association) Surge Protection Institute (NSPI):

It is also estimated that the typical RV can be bombarded with dozens of power surges per day. Power surges come from three sources; the electrical equipment within the RV itself, nearby lightning that is induced into the power poles, and from grid switching at the electrical utility.

Every time the Air Conditioner starts in your RV, it could send damaging power spikes to the remainder of your gear. Many RV appliances; circuit boards for the refrigerator and water heater to name a few, often have surge suppression for the DC power system to protect against the start-stop cycles from the water pump. In fact, it is my contention that lack of surge suppression on the DC power grid is one factor in LED lighting damage.

While I have written an article on DC Surge Suppression in your RV, a similar issue exists with AC Surge Suppression. What is so insidious about surge damage is it if often "latent damage". When that expensive refrigerator quits working for no reason, it could have been due to a damaging surge your RV received a month ago. Surge damage also is accumulative. The constant bombardment of power surges over time may be enough to finally damage your equipment and appliances.

An effective solution to combat surge damage is the MOV, or Metal Oxide Varistor. The typical RV Surge Suppressor is comprised of one or more MOVs. A MOV is a solid state device that acts like a voltage controlled switch. MOVs are available in a wide range of voltage and energy dissipation values. In the typical configuration, the MOV's voltage is selected so it does not "close" until the voltage surges above a certain point - typically 25% or more of the base voltage. When the MOV closes, that voltage is shunted to ground, thereby protecting the devices.

One thing that must be mentioned is MOVs do wear out over time. In that regard, I consider them "sacrifical". A well designed surge suppressor will contain MOVs that have a voltage rating high enough that it does not wear itself out too quickly, but low enough that it is effective in surge suppression. As well, when MOVs fail, they can catch fire if not removed from the circuit, so some method of disconnecting them is highly desired (overcurrent or thermal fuse).

Surge suppressors often include a detection circuit to check for reversed wiring, open ground, and other wiring faults.

MOVs are typically used in parallel to obtain the desired energy dissipation. MOVs, and thus Surge Suppressors are typically rated in the number of Joules they can dissipate over a given period of time (usually in the microSecond range).

The best selection criteria is to obtain Surge Suppressors that are UL rated, and having the highest Joule rating you can afford. The UL rating is important for powerline devices, since the surge protectors are tested to ensure they behave in a safe manner.

Unfortunately, a surge suppressor may not be enough to fully protect your RV. The best protection is an EMS, which includes the functionality of the surge suppressor plus monitoring of the power line. If the power source's Voltage or Frequency is either too high or too low, it will automatically disconnect the RV, thereby preventing it's damage.

The primary issue here is brownouts, which are defined as a low voltage condition that can damage motors and air compressors. Anytime the incoming voltage drops below 104VAC (on a 120VAC power line), or 208VAC (on a 240VAC power line), damage to voltage sensitive devices can occur. Therefore the EMS has the ability to automatically disconnect the RV should the voltage go below the safe point.

Frequency is also monitored. While not a common issue of commercial power utilities, if you run a generator, your RV could be at risk from low or high frequency on the power line.

Part of the problem is how RV parks are allowed to supply power to RV sites. The 2017 Version of the National Electrical Code (NEC), Section 551 (RV Parks) allows a sizing criteria that might contribute to brownouts. A good explaination of this procedure can be found here Sizing RV Park Electrical Services using the NEC.

Consider a RV park with 10 campsites, each wired for 30A. The NEC requires each site to have the capability to provide 30A, but then allows the application of a derating factor for the total park.

For example, you would think that 10 sites having 30A service would require the park to supply 300A for the entire facility, but that is incorrect. The NEC allows derating the 10 sites by 50%, so that the park actually only needs to supply 150A.

The reasoning for this is the notion that not all sites will be occupied at the same time, and that each site will not require the full 30A simultaneously.

However as RV'ers, we know that is not always true. On a hot summer holiday weekend, the park will likely be full, and the power hungry RVs will be running their air conditioner(s) constantly.

Today's typical RV can consume a lot of power, with one, two, or three air conditioners, residential refrigerators, gas/electric water heaters, fake fireplaces, power slideouts, and everything else - a RV - especially one designed for 50A, but plugged into 30A service, can overload the power system.

When the power system demand is near to the actual supply capability, the voltage tends to drop - hence a brownout. So expect to have a low voltage condition when:

• The park is full.
• The summertime when everyone is running air conditioning.
• 50A RVs are running on 30A service.

The above description could be classified as a worst-case scenario, as the NEC also requires 20% (existing parks) to 40% (new parks) of the sites to be 50A sites. And the 50A sites will tend to mitigate the power issues. However, depending on the park layout, brownout conditions could occur at certain areas of the park and not others.

All things considered, an EMS is a necessity these days to prevent brownouts from damaging your RV. For the $200-300 cost of the EMS systems, they are well worth having the "insurance" to protect your RV. Afterall, one blown compressor in your RV's air conditioning system could cost more to be repaired.

Whenever there is a discussion of Surge Suppressors or EMS systems, someone will make the statement that they have been camping for 50yrs and never had an issue. Of course, this is likely true because RVs 50yrs ago were not the power hungry beasts they are today, and with a higher count of popup campers and tents, the RVs did not demand a lot of power. But these days, especially in those parks built 50yrs ago just cannot meet demand of the modern power hungry RV.

Without modification - no. Although most EMS systems do have a bypass, I do not recommend using it as you are simply disconnecting your RV from the protection of the EMS. On the other hand, the likelyhood you have power problems should be dimished since you are disconnected from the grid.

The problem with portable generators is most of them do not have the all importand safety ground to neutral. Their reasons are varied, but it could result in an unsafe condition should the RV be miswired. Running such a generator through an EMS system will result in an open-ground error, and the EMS will not energize.

Fortunately, you can purchase a "bonding plug" that does connect the ground and neutral together, which prevents the EMS from erroring out on an open ground.

Again, the answer is NO, at least for the Progressive Industries EMS systems. They provide no reason for why not, and I have not had the ability to test the theory. However, Inverters tend to have horribly noisy outputs, and I am thinking the reason is the inverter may falsely trip the EMS system. Other possibilities include some inverters may use a floating ground that is between the Hot and Neutral; for example 60V on the Hot lead and 60V on the Neutral lead in respect to ground. Again though, this is my conjecture.

At any rate, an inverter powering a RV is "off-grid" so you should not experience the problems the EMS is designed to protect.

As stated previously, only buy one of these devices that have been UL rated (or the equivalent approval authority in your locale). There is simply no excuse for not obtaining UL approval in my view. Either the company does not want to spend the money for testing, or the device does not meet the minimum requirements. Oddly enough, only a few RV surge suppressors on the market are UL rated; most are not. Either way, I highly recommend using only UL rated suppressors. And from my research, they are not really any more expensive than the non-UL rated offerings.

Next, purchase the highest number of Joules you can afford for the surge suppressor. The fact is, the higher the Joule rating, the better the protection.

Lastly, purchase the proper Suppressor or EMS for your RV. If your RV has 50A service, buy a 50A device. With the proper "dogbone" a 50A device will work on 30A. In fact, I know of no instances where it will not work. There is no need to buy both 30A and 50A devices if your RV has 50A service. And of course, if your RV is 30A, then buy a 30A protector.

As stated eariler, you can purchase a generator bonding plug if required. As well, depending on the hardwired version of the EMS you purchase, you can buy a second display unit (Progressive Dynamics EMS-HW30C or EMS-HW50C), or a remote display unit (Southwire 35530 and 35550).

The Progressive Dynamics "L" series (with internal display) are not remote display capable, however you can purchase the RBPSK remote switch which allows you to place the "disable" switch in a more convenient location.

And if you have a portable unit, you can get a locking "ball" that fits over the cord-ends to deter (not necessarily prevent) theft.

A second category of EMS systems are the so-called AutoTransformers. Rather than disconnect from the source, they aim to change the winding ratio internally to match voltages. For example, the autotransformer can boost the secondary voltage to the RV even though the primary voltage drops to below safe limits.

Unfortunately there is controversy surrounding these devices. NFPA (National Fire Protection Association) standard 1194 and NFPA 70 (National Electric Code) have banned AutoTransformers. While NFPA 1194 is not regulatory, NFPA 70 has been adopted by the federal and every state government, so it is regulatory.

As well, the Huges AutoTransformers are not UL rated (at least there is no evidence on their website). Rather than recommending or not recommending these devices, I have produced a video describing the controversy.

References:

Progressive Industries UL Rated Surge Suppressors and EMS Systems
Southwire UL Rated Surge Suppressors and EMS Systems

NEMA Surge Protection Institute (NSPI)