NEC 422.16 (b) (2) says this.....
(2) Built-in Dishwashers and Trash Compactors.
Built-in
dishwashers and trash compactors shall be permitted to be
cord-and-plug connected with a flexible cord identified as
suitable for the purpose in the installation instructions of
the appliance manufacturer where all of the following conditions
are met.
(1) The flexible cord shall be terminated with a groundingtype
attachment plug.
Exception: A listed dishwasher or trash compactor distinctly
marked to identify it as protected by a system of double insulation,
or its equivalent, shall not be required to be terminated
with a grounding-type attachment plug.
(2) The length of the cord shall be 0.9 m to 1.2 m (3 ft to
4 ft) measured from the face of the attachment plug to
the plane of the rear of the appliance.
(3) Receptacles shall be located to avoid physical damage
to the flexible cord.
(4) The receptacle shall be located in the space occupied
by the appliance or adjacent thereto.
(5) The receptacle shall be accessible