Plugged box into upstairs outlet.......problem solved. Now I can just get over having that big extension cord running through my house, then no problem.

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Have you got a GFI outlet on the same circuit? If so it could be wired wrong. Think back, about the time the problem started did you do any electrical work in the home? Or add a major appliance (for enstance a couple of years ago I installed a new over the range microwave and plugged it up to the same circuit as a window AC, everytime I turn on the microwave while the AC is on it trips the circuit)? Always try to put major appliances on their own circuits.