200.2 General. Grounded conductors shall comply with
200.2(A) and (B).
(A) Insulation. The grounded conductor, if insulated, shall
have insulation that is (1) suitable, other than color, for any
ungrounded conductor of the same circuit for systems of
1000 volts or less, or impedance grounded neutral systems of
over 1000 volts, or (2) rated not less than 600 volts for solidly
grounded neutral systems of over 1000 volts as described in
250.184(A).
(B) Continuity. The continuity of a grounded conductor shall
not depend on a connection to a metallic enclosure, raceway,
or cable armor.