Installed a hard wired one into my Coleman, 30 AMP. Measures voltage high and low as well as surge, and polarity.
The following year was in the trailer doing some cleaning, plugged a vac in to clean up the floor and Bang, power out. WTH? Check the breakers, none tripped, then about 3 1/2 minutes since bang, click, power back on. OK now I am scratching my head(I had forgotten I installed the guard unit). Start the vac again and bang. This time I heard it more clearly, coming from behind the power panel and the lightbulb came on in my head. So I go out and look at the extension cord. Sure enough the cord was corroded causing a line voltage drop. DOH! I went and bought 100' of 6/3 outdoor cord, two 30 amp plug/socket, a UL box with 30 amp outlet and 6/3 indoor cable and wired in a dedicated 30 amp supply to feed the trailer. No more issues after that and could run the entire trailer.
Going to do the same with my new trailer, though it is a 50 amp, and this time put a readout in so I can see the actual voltages.
