...   dictate
   that the wire be exposed externally so that it is visible.  My concern is
   that the wire will driven by 50 volts at 60 Hz from the secondary of an
   isolated step-down transformer.

           So here is the concern.  There is plenty
   of current available from this transformer secondary.  Is 50 volts enough
   to give a jolt to the happy art viewers if they happen to touch

WOuld painting the wires with shellac or some other kind of transparent lacquer
be an option? it should provide sufficient isolation.

        przemek