Interference is not the issue, when you see the amount of power and ethernet cables packed into racks in data centers with no issues.
Mostly it is a building code issue related to separation of electrical and low voltage cables. It is mostly for safety. The building code vairies and I forget the exact spacing. It is either 6 inch or 12 inch but I think it depends if the elctrical is in conduit or direct bury. In ether case 6 inch is more than far enough away that you will not see any interference from the electrical. Pretty much you would have to wrap you ethernet around the electical cable to get much interference.