I have a drop cord that I put  a box on the end of with two outlets.  I've used it without a problem.  I have the white and black wires where they belong and the green is attached where it belongs.  I then ran electrical tape around the outlet so no wires are exposed.  The incoming cord is fine and constrained with the proper fitting.

I was moving stuff around and picked up the box and placed it on the marker arm of the grain drill and saw sparks.  Moving it around on the marker arm produced a number of sparks like you were grinding a drill bit on a grinder. NOT sparks that were hot like sticking a screw driver in an electrical socket.

I took it to the shop and re-attached all connection, made sure nothing was touching the box and retaped the outlet.  Then took it back and I still get sparks.  I can see a slight burn pattern on the marker arm.  When I pick it up I don't get a shock or even a tingle.  I am not about to hold onto the drill and the box at the same time though.
This is the box I'm using.

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