Friday, December 1, 2023


What’s causing fluctuating line voltages in RV?

Dear Gary,
gary-736I have a 2013 Endeavor 43RFT. The Power Control System Central Monitor Panel is showing that the L1 and L2 voltages are fluctuating 3 volts every one to five seconds, (e.g., 118v then 121v then 118 then 121, etc.). Per Monaco Help Line, I have tightened all the screws in the distribution panel and in the transfer switch. This occurs whether I am on shore power or generator (but not when inverting). Monaco Help Desk could not offer any other help, how about you? My inverter is a Magnum MS-2812 and the transfer switch is Surge Guard 41260. —Jim L., near Huntsville, Texas

Dear Jim,
This particular transfer switch does not contain any electronic components and is reliable, so we can rule out any problem with that device. And your inverter likely produces a purer sine wave than that off the grid, so that leaves only the coach loads as the possible suspects since you’ve already addressed the connections (be sure you’ve checked and tightened them all). The next thing to do is to isolate the problem to a specific circuit, then locate the culprit component within that circuit. 

MH RV Doc RVT 751Start by powering up the coach (either by shore power or generator), and turning the branch circuit breakers off completely. Monitor the voltage with all the branch circuits disengaged; the voltage should not be fluctuating at this point (if it is, there’s likely a problem with the source voltage itself). Then turn on each breaker one at a time and allow the voltage to stabilize. If the voltage begins fluctuating after turning on a specific breaker … that’s the circuit with the problem.

Surge guard RV Doc RVT 751
Surge Guard

Next determine which component(s) that circuit is powering. It will likely be something equipped with an overload device that automatically resets such as the heating element in the water heater. Something is causing the current usage to fluctuate, which results in the voltage variances. If you cannot locate the specific component within that circuit, a voltage drop test can be performed to determine exactly where the current leakage is occurring. It could simply be worn insulation on a conductor somewhere if it’s not the actual “load” causing the fluctuation. Unfortunately, it is best left to a professional electrician, one with an understanding of RV electrical systems, to dig beyond this point.

You might want to refer to the coach wiring schematic to determine which components are on each circuit as a guide and have each component tested independently. Even though it may take a Certified RV Service Technician, the current leakage or fluctuation cause has to be there somewhere! It’s pretty much a divide-and-conquer troubleshooting process.




0 0 votes
Article Rating
Subscribe to comments
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Oldest Most Voted
Inline Feedbacks
View all comments

Alan Strihafka (@guest_1663)
7 years ago

If the voltmeter is digital, and it most often fluctuates between the 2 same values, it could be that the actual voltage is between the 2 displayed values, and the meter just can’t decide which to display. You could double check with a plug-in analog meter and see if the needle fluctuates.

My guess is that this is normal digital meter behavior and there really is not a problem.

GipCTravelers (@guest_1659)
7 years ago

Greetings Gary,

Voltage fluctuations are a natural result of many factors (i.e. Power Plants Generators and Distribution, , Local Distributions, Connections, Amp Loads, Wiring Sizes, Wire Type, etc). All play huge factors. Campgrounds are notorious for incorrectly sizing their loads and provide very little maintenance of their units once installed.

There are standards for fluctuations. Here are but a couple:

Even generators are notorious for voltage fluctuations as they are mechanical devices and the RPM on the generator cannot be kept at an exact RPM turn ratio. Especially as new loads are introduced such as the start up of an A/C unit. Start and Run Capacitors are added to compensate for some of this surge affect.

But the good news is that most devices are designed to operate within a “band” of ranges. An appliance rated at 120 Volts can operate usually anywhere from 105 to 128 volts.

As for the inverter, it is a pure sine wave inverter and they are designed to take a range of input voltages and provide a constant out voltage that does not change. Having said that, it’s important to purchase a quality inverter if you want durability as they do take on a lot of heat.

One item that all RVer’s should consider installing is a Power Monitoring System such as one offered by Progressive Industries. Low voltages, incorrect voltages, cross phasing, dropped neutrals, Lost Grounds, etc are but a few things that will cause your equipment damage. This system monitors this and will drop out power to your RV to prevent the damage in nanopseconds. It will allow you to investigate the problem and correct the problem before damage can occur. We have one on our RV and it has saved us a number of times. BTW…I have no affiliation with Progressive Products but I am a happy customer to date.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.