Fluctuating Line Voltages in Motorhome

I have 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 SurgeGuard 41260. Jim L. (Huntsville, TX area)

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. 

Start 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.

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.

##rvt751