Chapter 84 covers machines and appliances whose function is mechanical: engines, pumps, machine tools, data-processing equipment. Chapter 85 covers the electrical function. The question is not whether the appliance plugs in, but which function it performs.
Parts are the real trap, and they are not classified by judgement. Note 2 to Section XVI imposes an order: a part that is itself an article of a specified heading goes there; failing that it follows its machine; failing that it falls to 8487. Electro-mechanical domestic appliances with a self-contained motor belong to 8509.
Every number opens on the lines beneath it, down to the ten-digit classification number.