I had similar problems this spring with 50 amp surge guard. Would shut me off sometimes immediately, sometimes intermittent. Tested every power pedestal and all checked out good but still had the problem. In three different cases, three different parks I moved to a pedestal on a different circuit and problem disappeared. Any kind of fault will cause that to happen. In my case the voltage was never too high or low. It was detecting some kind of fault . In my case I think the surge guard was doing its job even though I think the coach would have been fine on the same power with out the guard. Mine is permantly installed