Burned out charger/converters, fried laptops, and air conditioners on fire, oh my!

One of the biggest hidden problems for weekend campers and full-timers alike is a lack of adequate electrical voltage at their campground. An innocent action like flipping on your air conditioning (A/C) unit or electric water heater might turn out to be an expensive week in the shop for your RV. This is why you need to watch the voltage coming in from shore power.

Most people know that a voltage spike can damage electrical equipment. What a lot of people don’t know is that low voltage can be just as bad. This is particularly true in equipment with mechanical motors. Appliances like air conditioners and refrigerators,  may increase the amount of current (amps) it draws in direct relation to the dropping voltage.

These are the devices every RVer should bring with them and know how to use!  When they go camping, these will help keep their electrical devices safe and their RV out of the shop:

If that sounds like a bunch of technical jargon, that’s ok (and perfectly normal). In plain english, it’s four plastic boxes:

Shore Power Monitoring Devices: EMS-PT30C, Kill A Watt P4400, BackUps RS-550, Multimeter
EMS – Kill A Watt – UPS – Multimeter
  • An EMS Surge Protector watches for problems from the campground power grid outside the RV (about as hard to use as a smoke detector and just as important).
  • A Kill A Watt® line monitor watches for problems related to your devices inside the RV.
  • A UPS battery backup has a battery in it to keep your more important devices running for a few minutes if the power becomes unsafe/unstable. (I’m looking at you California brown-outs)
  • A digital multimeter has probes to check your electrical systems if a problem does arise.

Low Voltage—Who drank my juice?

Understanding Shore Power Technology: Voltage = Juice : Amps = Pulp
Voltage = Juice : Amps = Pulp

More voltage allows more amperage to flow safely.

If you don’t care about the technical bits or want to miss out on a cute analogy, skip on to the next section.

Common sense would tell you that if the voltage gets too low there wouldn’t be enough juice to power your devices and they would simply turn off or stop charging. Unfortunately, this is one of those times where common sense is wrong. Instead, they are more likely to overheat.

Some newer devices have protection against low-voltage overheating by using a switching power supply or by automatically turning themselves off. This, however, is not usually the most important ones in your RV—the refrigerator, the A/C unit, and the charger/converter. Laptops more than a few years old may also be prone to overheating.

It’s a common misconception that volts alone make up the juice that powers things. Electrical current is delivered via both volts and amps. If volts are the juice then amps are the pulp. If there isn’t enough juice to keep things flowing the pulp clogs things up pretty quickly. In terms of electricity, the clog forms as heat buildup at high resistance junctions.

For our purposes here, amps = heat, and in the world of electricity amps are an on-demand service. If the amps are available (and they always are from the power grid) then your devices will insist on having them, regardless of whether there’s enough voltage to carry them.

If your neighbor flips on her A/C, she’s basically drinking some of your juice. There’s plenty of pulp (amps) but everyone is sharing the juice. The more juice (volts) currently being used, the hotter your devices get.

If you are in a park with a lot of seasonal residents, you may find that 5:30pm can be a bad time for the electrical grid. Unfortunately, most parks operate beyond their electrical capacity. When everyone comes home and flips on their A/C and big screen TVs—like magic—everyone’s local wiring heats up. Tada!

Basically, voltage allows the required amps to flow safely to and through your devices. When the voltage drops, some devices (including anything with a motor) request more amps to make up for the loss. Those devices and the lines going to them heat up.

Example: A 150W light bulb (watts = volts × amps) burns brighter than a 60W bulb because it burns hotter at the same voltage. It burns hotter by providing less resistance. In turn, it draws more amps from the main line and pushes it through the same tiny space.

You don’t want to make your air conditioner “brighter”. Campgrounds have fire pits for that.

But I paid for a 30/50 amp spot!

When dealing with shore power, what you pay for isn't always what you get.
You get what you pay for.

You paid for amps, not volts. If the voltage drops, more amps is bad.

When you pay for a 30 or 50 amp spot, that’s exactly what they give you—a bigger fuse. With a bigger fuse, you are ensured that your lines won’t overheat when your devices ask for more amps. Now, if only you could pay for a 120 volt spot you’d be all set!

When a campground on an insufficient electrical grid can’t give you the volts you need to carry the amps your devices want, you may just find yourself with a fried device or two. If you’re lucky, you’ll only lose a blender. If you’re unlucky, it may be your computer, fridge, or air conditioner.

The more amps a device uses (like your A/C unit) the more likely it is to burn out or catch on fire. Granted, fire is an extreme case, but it certainly does happen.

So how should I monitor my shore power?

Here are the quick step-by-step details on how to use each of the four shore power monitoring devices we talked about earlier in this article. This is obviously not everything you need to know, but it will get your on the right track to protecting your equipment.

Use an EMS Surge Protector

Technology: Electrical Management System by Progressive Industries - Portable 30-amp Surge Protector with Voltage Protection
Electrical Management System (EMS-PT30C) by Progressive Industries

First off, and we can’t stress this enough, buy an Electrical Management System (EMS) based surge protector. It plugs in between the shore power’s electrical box and your RV’s electrical line. One plugged in, it watches the incoming voltage and the amperage you are using.

A EMS will cut shore power if there’s a distribution problem. One example where this happens is if you try to draw too many amps. Another is if the voltage gets too low. It also cuts the power if the voltage spikes or is too high, much like a standard surge protector does in case of lightning strike.

Unlike a standard surge protector, it’s outside your RV, so instead of just protecting your devices, it protects all of your RV’s wiring and electrical systems.


Progressive Industries makes the most popular EMS boxes. We use their 30 amp model in my RV, the EMS-PT30C. You can order one direct from the company, but they tend to take a few weeks for delivery. Buying from one of our links to Amazon will save you some delivery time as well as some extra cash.

The price is steep, but if you pack a smoke detector to detect a fire then it is just as important to pack an EMS to prevent one.

Use a Kill A Watt®

Technology: Kill-A-Watt Line Monitor by P3 International
Kill A Watt Line Monitor by P3 International

The Kill A Watt® line monitor by P3 International monitors a number of electrical stats in real time and displays them on a small screen above the outlet. It can even be programmed to calculate how much money you’re spending if you pay by the kWh (for seasonal RVers).

Leave a Kill A Watt® plugged into a visible outlet inside your RV. To set it up, just press the “Down” button until it shows you the current line voltage. Now, at a glance, you can tell if the campground is operating over capacity (and if your devices are at risk) because you can see how may volts are available at the outlet.

Another great use for a Kill A Watt® is testing a newly purchased device. Press the “Down” button until it shows “amps” or “watts” mode. Now plug in your new device through the Kill A Watt®. Soon you will see how many amps it’s drawing (make sure you don’t exceed your shore line capacity) or how many watts it’s using to estimate seasonal usage cost.

Use a UPS (optional)

Technology: APC BR1000G Back-UPS Pro 1000 Uninterruptible Power Supply
Uninterruptible Power Supply by APC (BR1000G)

An Uninterruptable Power Supply (UPS) battery backup automatically switches to stored backup power if shore power cuts out or the voltage falls outside a safe range. They’re most commonly used to give computers enough time to shut down safely when the power goes out, but they can be used for a lot more than that.

A UPS is entirely optional, based on your needs. It’s practically a must-have if you use a desktop computer without its own battery. Otherwise, you may just want to carry one to keep your TV or Wi-Fi router running.

Note: They can be heavy. This is the biggest reason not to carry a UPS. Essentially, they are a portable battery bank with their own built-in inverter. They tend to be heavy for their size because, like your coach batteries, they usually consist of a couple lead-acid batteries (but smaller).

They don’t carry nearly as much power as your coach batteries, though. Even the biggest consumer ones will usually only keep your equipment going for 30 to 45 minutes, depending on power consumption.

Just like inverters, they come in True Sine Wave (TSW) and Modified Sine Wave (MSW) options, with TSW typically costing significantly more.

Keep a multimeter around in case of trouble

Technology: INNOVA 3320 Auto-Ranging Digital Multimeter
Digital Multimeter by Innova (3320)

Some people would say a multimeter is optional. Those people like paying their repair shop’s hourly rate for electrical troubleshooting more than we do.

A digital multimeter with the essentials is fairly affordable. It should cost between $15 and $30 (USD), depending on features. Check out the automotive section at your favorite big box store or anywhere that sells home electrical equipment.

The most common and basic use for a multimeter in your RV will be to occasionally check the precise battery charge and/or the voltage coming in from your 12V DC (direct current, i.e. battery powered) sockets (the “cigarette-lighter” plugs).

When you run into problems, you can also use a multimeter to test electrical lines for ground shorts, faulty wiring, and burned out components. If nothing else, when the repair shop says you need new batteries you can verify it for yourself.

More on batteries

Technology: Testing Voltage On Batteries
Check your batteries often.

Protect your devices

Luckily, devices designed to run on 12V DC battery power have low-voltage protection built in and will dim or turn off when the juice gets low. This typically includes your house lights, refrigerator control board, and maybe even your TV.

However, if you use a basic inverter to run your AC (alternating current, i.e. a wall socket) powered devices, when the DC line voltage gets too low so will the inverter’s AC output voltage. This could lead to another potentially dangerous low-voltage situation. Note: Some of the more expensive inverters have multi-step transformers and an auto-shut-off feature to avoid low-voltage problems.

Protect your batteries

If you regularly run your coach batteries down below 50%, you will severely shorten their lifespan, so it’s best to make sure you keep them charged. But their voltage drain can also affect the rest of your devices.

Assuming you’re using 12V batteries (and you have a multimeter), you can consider them fully charged above 12.7 volts and drained (50%) around 12.2 volts.

Most batteries will read high after charging—often over 13V when they’re fully charged—due to what’s called a “float charge”. For a more precise reading, turn on your house lights for about 5 minutes and then check the voltage.

Keep your batteries above 12.2 volts (and topped off with distilled water for wet-cell batteries) and they should give you 3–5 years of regular use.

Geek Bonus—Dangers of the “mathy bits”

Technology: Geek Bonus - The Mathy Bits
Watts = Volts × Amps

Watts = Volts × Amps

Your devices are usually rated in Watts (-W-). This represents the maximum amount of amps (-A-) the device should draw at the expected incoming voltage (-V-). In the US, that expected voltage is 120V (240V is common in other parts of the world).

So in the US, a rating of 60W (common for laptops) means a maximum draw of 0.5A at the expected 120V. A 150W light bulb uses a steady 1.25A. You could be powering two laptops for that much power. My, how far technology has come.

The Danger

If the voltage drops, any device with a motor or unregulated power supply may increase the amps (and heat!) to maintain the expected wattage.

Hopefully we were able to provide a basic understanding of how your RV’s electrical systems work. The next time you pay for electricity at a campground, you’ll know what to look for and how to spot low-voltage issues before they become a problem. With the tools above, you can be sure that your rig’s power supply is, and continues to be, within a healthy range for your all your tech toys, gadgets, and appliances.

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can i put a surge protector in between two shore lines