why are some electrical plugs the same width on both prongs or have three instead of two prongs?

Question

Prongs might not be the right word for it.

In: Engineering

Answer 1

The third “prong” is ground. It is for safety of appliance and people when there’s too much electricity.
Phone charger doesn’t need it because it uses just a little bit of electricity. But washing machine needs big amount of power to operate so it must be grounded.
Of course it’s more complicated, but this gets the idea.