Don is a retired engineer and long-time motorhome owner who enjoys helping readers deal with the increasingly complex technology of RVs.
A Typical Standard Digital Multimeter
RVs Will Have Electrical Problems
Like it or not, your RV will eventually have some kind of electrical problem occur.
Most RV owners have little or no knowledge of the many electrical systems in their RV, how these systems operate, or how they should be cared for.
So, when something stops operating in their RV, they don't know what to do.
And of course, when they do ask someone else for help with resolving their problem, they're often told to use their multimeter and check for a certain voltage reading in their RV, but often they have no multimeter and no idea how to use one.
This article has two parts:
- A simple overview of the kinds of power systems used in an RV, from the small pop-up camper to the large, expensive motorhome.
- A discussion of what a multimeter is, what it can measure, and a few tips on how to use it properly.
Every RV owner should take the time to read through this article and get a good overview of what a multimeter is and how to find some of an RV's electrical problems.
RVs have several different power systems built into them, propane and electric. Some RVs will only have one or two of these electrical systems in them while a large motorhome might include all of these different electrical power systems to power the many accessories and appliances in the motorhome.
Electricity Can Kill!
Electricity can kill a person if they make mistakes when a person is working around electrical power sources. No inexperienced person should attempt to test or repair electrical problems without proper training.
The Propane System in Your RV
An RV will most likely have propane tanks mounted on it somewhere.
These propane tanks are there to provide power for such appliances as your:
- two-way fridge (110-VAC and propane),
- furnace (propane only),
- hot water heater (110-VAC or propane),
- gas range top (propane only)
- and in some RVs, your gas oven, though RV's from the past decade are likely to come with a more efficient convection microwave oven instead for use when baking.
DC Electrical Systems
RVs will have one or more 12-VDC power systems in them that are used for interior equipment.
A camper trailer or fifth wheel trailer will only have one 12-VDC system, often referred to as the MAIN (or CHASSIS) system, while a motorhome will also have a 12-VDC system, referred to as the AUX (or COACH) system, which is there for powering these interior accessories in the motorhome.
The engine's 12-VDC system, often called "CHASSIS," is like the electrical system in a regular automobile or truck. It consists of a battery and alternator along with electrical features typically found in automobiles, such as the radio, dash lights, headlights, and running lights.
On a camper-trailer, the difference from a motorhome is that the AUX system will also power the camper’s running lights, power awning, and power entrance step, while the towing vehicle's electrical system will power any exterior camper lights such as the running lights, brake lights and signal lights.
The AUX system consists of one or two 12-volt batteries (or two or four 6-volt batteries) configured to provide 12 VDC for the camper's interior auxiliary devices. These include the interior lights, gas and fire alarm boards, two-way fridge control circuit board, RV power control panel, etcetera.
These AUX batteries are kept charged by the built-in converter (charger) when the RV is plugged into an external 110-VAC source.
Breakers and Fuses
Electrical systems in a camper or motorhome are protected by circuit breakers and fuses. Typically, the AC voltages are protected by breakers and the DC voltages are protected by fuses which are normally standard automotive fuses.
Because of the heavier wiring used for AC voltages, you will find the breaker panel is usually located near the area of the external power input.
Some of the DC fuses will normally be located in the standard automotive circuit fuse panel located near the engine or sometimes under the dash.
There will be another fuse panel for the RV related equipment that runs on the AUX or CHASSIS battery system. It may be located almost anywhere in the RV.
AC Electrical Systems
External AC Voltage
During the mid-twentieth century, campgrounds started offering electrical hookups at their campsites for RV owners to use.
Because the RVs of that time had little or no electrical equipment in them, campgrounds just had to provide one or two 110-VAC connections with maybe a maximum of 10-15 amps of current.
Over time, though, RV manufacturers added more built-in electrical equipment into their RVs, and campgrounds started to offer 30-amp 220-VAC service at their campsites. Eventually, as the equipment list grew, campgrounds had to offer 50-AMP 220-VAC service.
This is why, when you open the cover of the power box at your campsite, you will see multiple different power breakers and receptacles for each of these types of RV electrical power hookup:
- 50-amp, 220-VAC 4-pin connector and a double breaker.
- 30-amp, 220-VAC 4-Pin connector and a double breaker.
- 15-amp or 20-amp 110-VAC 3-pin connector with a single breaker.
In fact, the owners of some of those really big motorhomes will often have to call ahead and find a campground that has sites with dual 50-amp (or 100-amp) connections in order to power everything in their camper. Otherwise they will have to get by on a single 50-amp service.
Generator AC Voltage
As motorhomes evolved, boondockers (campers who use their RVs without any external power) started demanding motorhomes with generators installed.
When a motorhome has a built-in generator, the owner can operate their RV’s appliances and other accessories regardless of where they might be camping.
These installed generators are designed to be capable of providing enough current for all of the electrical systems in their RV to operate properly.
This is why you will usually see a 5500-watt generator in an RV that has a 50-amp external service, because that’s exactly the power needed to operate everything in the RV.
If you do the math: 110 volts (110-VAC) multiplied by 50 amps equals 5500 watts.
But an RV owner should realize these installed generators are not designed to operate ALL the extra appliances, tools, chargers, et cetera that you might plug into the receptacles.
AC Voltage Control Systems
All 110-VAC power in an RV, regardless of whether it comes from an external AC voltage source or a built-in AC voltage generator, will go through the RV’s AC transfer switch before it goes to the main AC breaker panel for distribution to everything in the RV.
There is a power control panel in each RV which does several things for the owner.
Power selection. Because a camper can be plugged into external power and the owner can also turn ON the generator, the control panel senses whether there is generator power present and if it is, it will operate a "transfer switch" that makes sure there will only be one power source allowed into the RV at a time.
Power allocation. If you plug your big 50-amp RV into a campsite power box that only has 30-amp service, the power panel will allocate the power available to only as many of your large power-consuming appliances (like air-conditioning units, washer-dryers, hot water heaters) that can be operated safely with the limited 30-amp power available.
GFCI. Receptacle System
RVs also have GFCI systems built into them. These systems operate the same as they do in a home; if they sense any small current flowing between the common wire and the ground wire, they will “kick OFF.”
This capability protects people using an appliance plugged into the GFCI receptacle from any "leakage" current flow.
Most GFCI receptacles will be connected to several other receptacles. These “slave” receptacles are usually in places where a person using an appliance might also touch something grounded. You will usually find these slave receptacles in the kitchen area, the toilet area, and on the outside of the RV.
The master GFCI will have two buttons on it; one marked “test” and the other marked “reset." If the GFCI kicks out, you can easily reset it with the reset button.
Using a Multimeter Safely
I do not recommend that an unskilled person try to make certain measurements themselves. Measurements that require wiring to be disconnected and tested, for example current measurements, can be extremely dangerous for an experienced technician, much less a novice.
But you can measure a DC voltage or even an AC voltage safely if you make sure not to not touch any connections or wires that might have power on them.
You must always be careful when you’re using a multimeter, because when you use one, you are placing the probes of the meter’s leads onto "hot" connections. This is always dangerous. So make sure you observe the following safety suggestions;
- Before you start, make sure all power is turned OFF.
- Never place your hands on a bare wire or an electrical terminal.
- Only touch the insulated part of your meter leads and never touch the metal tips.
- It is smart to wear a pair of insulating gloves when making measurements.
- Once a measurement is made, remove the probes from any connections or terminals and place them safely out of the way.
- As soon as you make a measurement, write the reading down for reference later, as well as which terminals, connectors, or wires you checked.
- And the thing most often forgotten by multimeter users; Turn it OFF before you put it away.
The key to checking for a suspected electrical problem in your RV is to use a multimeter for the job, and you will find that it pays for itself quickly when you can find a simple electrical problem yourself.
But, again, ALWAYS take all SAFETY precautions when you are dealing with electrical problems in your RV.
What Is a Multimeter?
An experienced RV owner will usually have a multimeter somewhere in their RV.
A multimeter is a device that you can use to make electrical measurements in your RV: for example, to check if an appliance or piece of electrical equipment has power to it.
Making such quick measurements is a troubleshooting step that almost any RV owner can do with a minimal amount of training with the multimeter.
The multimeter gets its name from the fact that it is capable of making multiple different measurements: voltage, current, and resistance (or continuity).
It’s a great tool for a skilled electrician or any RV owner.
Troubleshooting RV Electrical Problems
- Troubleshooting and Repairing RV Electrical Problems for the Beginner
How to troubleshoot common electrical problems that may cause breakers to trip and fuses to blow. Information on fuses and resistors, power drawn by common appliances, and electrical terms and abbreviations.
How Much Should You Pay for a Multimeter?
I’ve seen RV owners pull out multimeters and even complex electrical testing equipment costing hundreds of dollars, that someone sold them telling them they needed it. These RV owners usually had no idea how to use these things.
Even though I am an electrical engineer, I only carry one piece of electrical testing equipment in my RV: a multimeter.
And, when I need to purchase a new multimeter, I wouldn’t pay more than $50-$70 for a good one. All you really want a multimeter to do is:
- Have a digital display with large numbers
- Have an auto-range function so that it steps up or down to a reading of the highest accuracy.
- Operate on a 9-volt battery.
- Measurr AC voltages
- Measure DC voltages
- Have a nice flexible pair of insulated meter leads with protected metal tips.
- Measure continuity (resistance), for those occasions where you suspect a wire is not connected on one end or has been broken.
And that’s it. Measuring anything else is not necessary most of the time anyway, and once you go beyond these simple AC and DC voltage measurements, you most likely will need to hire an electrician to find your problem anyway.
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This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.