Wednesday, September 28, 2016

An EMS Unit For Your RV

Very often on various RV discussion groups and forums someone will ask what "surge protector" should they buy for their RV.  When I see this question I have an answer all ready for them and that answer is "You do NOT want just a surge protector for your RV, you WANT an EMS unit got your RV." So what is an EMS unit?

An EMS unit is an Electrical Management System. What this does as both act as a surge spike protector but more importantly it also will shut down all AC power going through the unit and into the power cord for your RV when it senses that the voltage coming in is either too high or too low. Why is this important? AC 110/120 volt power needs to flow in a certain range of voltage with a minimum and a maximum not to do harm to an electrical system and electronics connected to it. The damage that can be done when power flows out of that range can cost a great deal to repair. This unit will shut down voltage below 104 volts and above 132 volts. This may seem like an unlikely situation to occur but at campgrounds it can be quite common. At a crowded campground with a lot of RVs pulling off the power lines of the campgrounds I have seen voltage go below 110 volts. And on the other end, at campgrounds where there are few RVs at the campground which means few RVs pulling off power at the same time, the voltage is up near 130 volts. It does not take much change to put that voltage above or below the limits.

With one of these units you also get surge spike protection so should there be a sudden spike or surge or a lightening strike to the power lines the EMS unit will clamp down and cut off that surge or strike and not allow any damage to your electronics.

Both of these functions work differently. If a spike or surge comes through, the circuit physically breaks - in fact - like any surge protector that you might use at home, the unit will become dysfunctional in all ways should it need to clamp down on a spike of surge. If that happens what you need to do next depends on which company's EMS unit you own - and I will go into that later. If there is a voltage variation high or low, the unit will shut off power only temporarily until the voltage returns to within the proper range. The unit is still fully functional and it will turn the power back on when it is safe.

These units also test the polarity of the outlet you are plugging into and will not turn on if the polarity is incorrect. This means that the campground box outlet has been wired incorrectly or a wire has come loose or is off. This has to do with the outlet being properly grounded. This is also a very important thing to be certain of when plugging into any campground. If the unit shows the polarity to be wrong, you then need to go to the campground office and tell them and you will either need to be moved to another site with a correctly working outlet or campground maintenance will need to come and repair their outlet so that it is safe for you to plug into.

These units are not inexpensive. They sell for between $250 and $350 for a 30 amp unit and more for a 50 amp unit. They also come in versions that are portable - you plug the unit into the campground box and then your RV power cable into the unit OR that are hardwired. You have the unit installed into your RV's power connection which generally means cutting your power cable inside the RV and wiring the EMS unit between the power connection and your power cord. Both work exactly the same and offer the same protection. There are two main companies that manufacture these units - a company named "Surge Guard" and a company named "Progressive Industries". It is important to know that these companies also make just surge units that sell for much less - around $100 but even though these are made for RVs you are wasting your money if you don't buy the EMS model. The added protection that it provides is worth the money you will have to pay for it. You must think of this as paying for insurance. If you never need to make a claim it was there to protect you anyway - but when you need to make a claim on your insurance it pays you back - just like the protection an EMS unit gives if or when it goes to work and does its job.

The two companies units provide the same protection and do it equally well. There is one difference between the two companies that did not exist when I bought my unit which is a Surge Guard. That difference is the warranty and that warranty is what makes the difference in my reference above. The Progressive Industries EMS unit has a lifetime warranty which apparently covers the unit if it is hit with a surge/spike. The unit can be repaired with a replacement circuit board which the company will provide. I cannot say if they will provide this without charge. With the Surge Guard unit if a spike happens the unit must be discarded and a new unit be obtained for use. This would make it seem that the Progressive Industries unit is the preferred unit to buy. Perhaps.

There are two other non-performance dissimilarities to consider if buying a portable unit. The Surge Guard has a power cable with plug coming from the top and a power cable with socket coming from the bottom. Both plug and socket have a pull handle that makes it easy to pull the unit both from the power box and off of your RV power cable. In this regard the Progressive Industries unit has a very short power cable on top with its plug and its power socket is in the middle of the unit. There is pull handle on the plug or the socket. With how hard it can sometimes be to pull RV power plugs and sockets apart those handles actually are a big benefit. The other thing to consider is that the Progressive unit has a small ring on its power cable to put a padlock through and then get that padlock somehow attached to the campground power box so that this $300 investment will not be stolen. Surge Guard has its own system which is a purchased option to prevent theft. It is a box that locks around the RV power plug and the EMS unit's socket preventing anyone from pulling the RV cord and unit apart and taking the EMS unit. I have that box and while it can be a pain in the a** to put together and lock, it does work.

These are the models to look for from each company -

Progressive Industries  - Model EMS-PT30C (This is the 30 amp portable.)
Surge Guard - Model 34830

When you plug in the EMS unit there will be a delay before it passes power through to your RV. The delay takes about two minutes and 15 seconds - and those can be the longest two minutes and 15 seconds to wait to see if all is well and you have power. The delay is there as a feature and more protection should the unit stop power because of a voltage variation and not just start back immediately which if an air conditioner had been on and is still turned on, the power restarting will not damage the air conditioner.

I will conclude with a recent experience we had at a campground recently. We were plugged in and in for the night. The Surge Guard was connected and working. We were inside watching television. All of the lights were on and the air conditioner was running. We had been in for about an hour and a half. Suddenly, the television went off, the air conditioner stopped and when I looked over to the microwave the display was dark. The lights were all on - and it took me a minute to realize that the AC power was out - the lights stay on because they are powered - even when plugged in - by the coach (RV) batteries. Why was the power out? My first thoughts were that there was something wrong with the Roadtrek. I went through what it could be inside and was not coming up with anything. I then decided to go outside and see if someone walked through our site and tripped over our power cable pulling it out of the box. We had no power about ten minutes when I got outside and saw that the Surge Guard had power coming into it but the connection light was flashing. One of two things had happened. There was a voltage variation and the Surge Guard shut off power to protect us or the campground lost power and the power had come back on and the Surge Guard had to go through its delay to put power back into our RV. Power came back and all worked again. Later, very early in the morning, power went out again - and then came back on. I went to the office that morning and told them and they were aware that the power had gone out all over the campground - and we were assured that it would be fixed. Did the EMS unit come into play in this incident? Maybe. Did it remind me that one must always plug in at a campground using an EMS unit? Absolutely!

Some feel that they don't want to pay what an EMS unit costs? Some say that they have never had a problem. I am reminded of what Dirty Harry said - "Feeling lucky?" I know RV owners who have had had the EMS unit do its job and saved them from expensive damage. I also know of RV owners who wish that they had one when they found out what the repair bill was to replace most of the electrical system in their RV after a voltage variation. You decide. Maybe you will be lucky. Maybe you will not.


  1. This was an excellent post. I never knew about an EMS unit and think this is by far, the way to go. Whenever I get to travel, I want my unit well protected. Do you happen to know if one of these units would be necessary if one was operating on solar? If I understand correctly, this is not a unit you can just unplug if boondocking???

    1. These units only provide protection from power coming into your RV through the power cord plugged into an 110/120 volt electrical outlet. They have nothing to do with the power coming in through solar panels, an on board generator, or using an inverter with your battery bank (or solar panel).

  2. Good article Robert,in my research I read somewhere that these units wearout over time,any info on the shelf life?

    1. According to Surge Guard - on their website FAQ - the surge circuit will last indefinitely. I can only assume that the Progressive is the same. Also these units self-check and also check the circuit when they are starting up.