Electrical question

The open ground is referring to the safety ground. As long as nothing shorts out to the frame, you are fine without it. For decades, houses were wired with hot and neutral but no safety ground. My sister inherited our parents' house built in 1957 and is remodeling it. It has no 3 prong plugs because it has no safety ground wires, anywhere. (She is replacing all of the electric so she will be properly grounded when finished.) Where the safety ground is useful is when something does short a hot wire to the frame. That energizes the frame and you can get a nasty, potentially lethal, shock if standing on the ground and touching the frame. The safety ground, however, immediately shorts that hot wire out to trip the breaker.