I think that something to always keep in mind is; even though a guy checks the electrical system out with a meter or test light of some sort before you plug in, something can happen later. This all dawned on me when I experienced some goofy voltages last summer. Before I hooked up, the 50 amp outlet was fine. Later, my little single circuit voltage monitor went off; indicating an open ground. That issue resloved itself but that should have been a warning to me and I continued on. Later, the little monitor went off again for high voltage. I moved the monitor to another circuit and it had low voltage. What had happened was that the neutral/ground bond was lost at the recepticle; causing crazy voltage on each leg. The installer of the outlet had not run a separate ground wire but had run a jumper from the neutral lug to the ground lug of the outlet.
The moral of this story is that a "surge guard" or EMS will keep watching the electric side of life after you have plugged in. There is no gaurantee that even though you checked the electric system when you hooked up that it will continue to be proper.
