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.


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Alan Strihafka
Alan Strihafka

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.


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: https://www.powerqualityworld.com/2011/09/voltage-fluctuations-flicker.html https://www.powerqualityworld.com/2011/04/ansi-c84-1-voltage-ratings-60-hertz.html 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… Read more »