Dishwasher with driven spray arm for upper rack

An automatic dishwasher comprising:

• a tub defining a wash chamber for receiving utensils to be washed;
• a first rack located within the wash chamber;
• a second rack located within the wash chamber above the first rack and selectively moveable between a loading position where at least a portion of the second rack extends exteriorly of the wash chamber and a wash position where the second rack is located entirely within the wash chamber;
• a spray arm carried by the second rack, with the spray arm being movable within a range of motion and having at least one outlet for introducing liquid into the wash chamber;
• and
• a drive system having a power unit accessible from the wash chamber and a drive unit carried by the second rack and operably coupled to the spray arm for moving the spray arm within the range of motion;
• wherein the drive unit is selectively coupled to the power unit when the second rack is in the wash position whereby the power unit provides an operating force to the drive unit to effect the rotation of the spray arm.