Double Insulation

Some electrical plugs have only two pins. These appliances do not have an earth wire. Instead, they have double insulation to protect users from electric shocks.
Two levels of insulation
  1. The electric cables are insulated from the internal components of the appliance.
  2. The internal components are insulated from the outer casing.

Appliances with this feature normally have non-metallic casings (like plastic casing).
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