How should a 2-prong outlet be grounded?
We recently purchased a house built in 1960. During our inspection, we found out that many of the outlets in the house are not grounded. A few of the outlets were grounded at some point, but the prior owner put 3-prong plugs/covers on all the outlets. The prior owners refused to have all the outlets grounded, claiming it would make a mess of the walls, but they put 2-prong outlets back on the ungrounded outlets so we could tell which are safe to use.
We are hiring an electrician to ground the outlets in the room that will house our office and exercise equipment. We will be plugging in computer equipment, an elliptical machine, TV, etc., so we want to make sure the work is done right for safety and so our equipment does not get fried. A GC we know said his electrician can ground the outlets for $33 per outlet. He said it is something that is done at the outlet itself, they do not have to run anything to the main panel. The electrician is coming over tomorrow, so we will ask him exactly what he plans to do, but before we talk with him, I want to know the proper way to ground an outlet so I know if what he is proposing as a solution is proper.
So, how should an outlet be grounded? How much wall damage should we expect? TIA!