If you are building a new Duo-Art then you would have to put in new
connectors of the grounded type.  You would have to get the device to
pass Underwriters Labs testing.  Modern codes require three conductor
wire and plugs with ground connection.

It would be ridiculous to go about changing the whole electrical system
in an 80-year-old Duo-Art to comply with codes made for modern devices.
The units we restore passed all federal and UL codes and requirements
when they were new.  If someone is stupid enough to turn on a
reproducing piano while the room is standing in water, then they
improve the gene pool by checking out of it when they do so.  I dare
say there has not been one single case of a Duo-Art electrocuting a
human.  Does anyone feel unsafe by turning on a player piano that uses
only two prongs on its plug?  I think not.

While I make sure everything in my shop is grounded, I would never add
grounding to an original system.  However, there were grounds of a sort
in the originals.  You may have noticed that there was often a wire
that attached from the label/case of the motor and ran to the cast iron
plate of the rotary pump.  I have also seen a ground running to the
plate of the piano.  On Ampico B there was a ground from the roll motor
to other metal nearby as well.  I suspect these were for bleeding off
static for some reason.  Perhaps someone can elucidate on the reasons
for these grounds.

D.L. Bullock   St. Louis
http://www.thepianoworld.com/