RV Electrical Tutorial

Chapter 13 - Surge Protection

Technically, a surge protector protects against surges in electrical power. But surge protectors as used in RVs do far more. In addition to surge suppression, the most popular surge protectors also protect against low or high voltage levels. Low voltage can be a common occurrence in campgrounds that have added sites over the years but failed to upgrade their electrical grid to keep pace with the increased demand. Low voltage can cause quite a bit of damage so it's important that you purchase a quality surge protector that includes over and under voltage protection as well. First let's define just what an electrical surge is.

An electrical surge is where the incoming voltage rises to a point significantly higher than what it's supposed to be. A voltage spike is similar but a spike is defined as lasting for one or two nanoseconds whereas a surge lasts three nanoseconds or longer. If the voltage is high enough it can damage your electrical devices. Earlier we talked about electrical voltage and how it is a measurement of pressure. If you get a sudden surge in water pressure you are apt to blow a hole in your fresh water supply hose but if you get a sudden surge in electrical pressure you are going to blow some electrical devices or sensitive electronics equipment. Surge protectors uses metal oxide varisters, commonly called MOVs. An MOV does nothing at normal voltage levels but when the voltage rises to an unsafe level the MOV will short that power to ground to protect any downstream electrical equipment.

A quality surge protector designed for RV use will also have both over and under voltage protection. Overvoltage isn't a real common problem in an RV park but it is a distinct possibility. Excess voltage will do the same damage as a surge except it's generally not as high a peak voltage but it lasts for much longer. The most frequent condition is low voltage at the campground pedestal. You may arrive at your campsite early and check your pedestal voltage with a voltmeter and find it within tolerance. However, once other campers arrive and start to fire up their air conditioners the voltage is likely to drop. Without an automatic surge protector you would have no protection against low voltage damage to your coach unless you constantly monitor the incoming voltage. A good surge protector will disconnect power to the coach should either low voltage or high voltage conditions appear. At that time you would have the option of waiting it out, running your generator, or using an Autoformer to boost the incoming voltage - more on that later. Quality surge protectors for RVs are available from SurgeGuard and Progressive Industries and are two well respected companies that offer their product through most major RV accessory sales outlets.

In the above image we can see two portable surge protectors. Portable units have the advantage of being able to be readily moved from one RV to another. This makes for a "zero installation" setup with no rewiring. Just plug it into the campground pedestal and plug the RV's power cord into the surge protector. The disadvantages are that it is out in the weather and could get stolen or vandalized. There are locking kits available to lock them to the pedestal but then you are trading the convenience of not having the initial install versus connecting it and securing it to the pedestal every time you go camping. If the pedestal's receptacle is very low to the ground it's possible that the portable unit may not fit because of the right angle plug and the bulk of the unit that needs to hang down from the outlet. One last caveat is that the hard wired units sometimes off a remote display option so that you can monitor the incoming power from inside the coach. With a portable unit you won't be able to utilize that option. The actual protection levels of the portable units are generally the same as their counterparts in the hard-wired segment so there's no advantage or disadvantage there.

Hard-wired devices do take a bit of installation labor but it's not that difficult. You simply mount the unit in the same electrical compartment that your RV's cord is located in. Remove the power cord from the transfer switch and connect the cord to the surge protector's input terminals. Then run a short whip cord from the surge protector's output to the transfer switch and you're all set. Some RVers choose to just cut 2-3' off the end of the power cord while some choose to buy another short chunk of cord from an electrical supply house. If you have a power cord reel you'll undoubtedly be getting a new whip. If your surge protector includes a remote display you will have to find a location for that display, mount it, and then connect it with a standard RJ11 modular phone cable. A cable is generally supplied but if you want to run a longer distance you may have to make a new, longer cable to reach the remote display panel.

Surges are rated in Joules. The bigger the surge, the higher the number, so you want to get a surge protector with the highest possible rating. The popular SurgeGuard 34560 is rated to handle up to 1,750 Joules of power surge. It will shut down power to the coach is the voltage falls below 102 Volts or is higher than 132 Volts. Various LEDs will inform you whether the receptacle is properly wired or has a bad ground, reversed polarity, or open neutral. If it shuts down the power due to low or high voltage or an open neutral wire it will reset itself once the power returns to within tolerances. There will be a two minute, 15 second delay before power is re-energized though to allow any air conditioners time to bleed off their head pressure. If you decide that you want to bypass the voltage cutouts feature and allow power through anyway you can defeat the unit by turning a key switch. In this mode you will still have surge suppression, however.

The Progressive EMS-HW50C is the gold standard of surge protectors. It's rated to handle up to 3,560 Joules of surge. Low voltage cutoff occurs at 104 Volts and high voltage cutoff occurs at 132 Volts. It comes with a remote LED display that is very easy to read. In addition to displaying the incoming voltage of both poles it will also display the amperage draw on each pole as well as the frequency in Hertz. If any pedestal mis-wiring is present or any shutdown has occurred the LED display will display a 2 digit trouble code that defines the problem according to the chart that is printed on the unit as well as in the owner's manual. The remote display can be mounted inside the coach or in the basement compartment. In this way it's handy to located the EMS-HW50C near the back of the compartment where it's easy to wire and still have the remote display located near the front of the compartment where it is easy to view. The bright LED is easy to read in bright sunlight and a bypass switch is located on the remote display to bypass the power shutdown function, just like in the SurgeGuard above. You have the choice of selecting either a 15 second power-on delay or a 136 second delay. Most modern air conditioners have a built in two minute restart delay so 15 seconds is the normal selection. You can also buy a second remote display that allows you to mount one in the basement and one inside the coach if you desire.

While the EMS-HW50C is the old standard, Progressive Industries also make the EMS-LCHW50 surge protector. The "LC" stands for Liquid Crystal display. Instead of a remote LED display, the LC series uses an integral liquid crystal display that is located right in the cover of the unit. The protection level is the same as its big brother but, depending on where the unit is mounted, you may have more problems in viewing the display. LCD screens just aren't as bright as LEDs and dark places and bright places are not their friends. Coupled with the fact that the remote LED display can be located anywhere and the LED holds a huge advantage. Still, the LC series does hold a $50 price advantage over its more costly brother.

Hughes Autoformer

Okay, once your surge protector determines that the campground voltage is below the minimum acceptable level it shuts down power to your coach. If you really want to power your coach you have some decisions to make. You can go turn the key or flip the switch to bypass your surge protector's low voltage cutoff feature. You have to wonder if that's a very safe thing to do though. After all, the reason it shut down is to protect your coach from low voltage. Remember that wattage is true power and volts times amps equal watts. If a device in your coach needs a certain amount of watts and the voltage falls, the amperage will rise and those excess amps will overheat and damage your circuitry. Another option is to run your generator. That may or may not be desirable, depending on your environment and neighbors. You can always wait it out in case it returns once the sun goes down and everyone's air conditioner stops running non-stop. Or, you can get an Autoformer.

An Autoformer is a voltage booster. While they do offer some surge protection, it's not very good. For this reason you'll still want a good surge protector. An Autoformer will automatically boost the incoming voltage. Models such as the Hughes Autoformer RV 450 will boost the voltage 5-10-15% as needed. That gives you the ability to take an incoming voltage as low as 91-92 volts and boost it to the minimum 104-105 volt cutoff that the surge protector needs to see. The Autoformer is always mounted first so that it boosts the voltage prior to the surge protector. If it was mounted after the surge protector it wouldn't work because it would kill any input voltage to the Autoformer. The Autoformer needs to see something before it can boost anything. The Autoformer is an optional piece of equipment. If you don't feel that it's that critical that your coach have power at all times or if you camp at nice RV resorts that have clean power you may not feel it is necessary. If you have a coach with a residential fridge and happen to encounter low pedestal voltage frequently then it may be a life saver that will save you from having to run your generator frequently. The Autoformer doesn't get very hot and it can usually be mounted in the same compartment as the surge protector and power cord reel. In that case a hard-wiring kit is available that let's you splice into the cord reel's output whip so that it can be inserted into the power cord whenever necessary. This keeps is it safe and dry rather than sitting next to the pedestal exposed to the elements and others.

Well, that about wraps up our tutorial on RV electrics. If you're game, proceed to the next chapter and take a quiz to see how much you've learned.

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