This cord is attached to another drop cord that is plugged into an outlet in the barn.  The outlet in the barn may not have a real ground.  It was put in by an electrician who is usually a little over the top about safety.  Though after reading your posts I'm wondering about the outlet.

I may take this to the shop where I know that the service is recently installed by a professional and is well grounded.

I'm completely confident that the drop cord and box are properly put together.  I used a wire stripper to remove the insulation and then the wires were soldered so no free little wires are sticking out.  And as  I said I just took it all apart and checked everything.  

Thank you.