Ok, I work with electrical engineers and posed the question about grounded vs. not grounded. They told me that grounded just means if it is grounded you are less likely to be electrocuted because the energized part can be sent to ground. I have an old model sewing machine from the 40s, all it has is a polarized plug. All that has ever went wrong with it once, the foot treadle went bad. I hope this helps.