Double insulation

Electric and electronic equipment is normally provided with basic insulation to prevent electric shock. In preparation for the failure of the basic insulation, some equipment is additionally provided with supplementary insulation, which is called double insulation. Double insulation is often applied to equipment that has a high risk of electric shock due to leakage current caused by water or dust.

For electrical equipment that requires grounding, the risk of electric shock is reduced by double insulation, so grounding may be omitted in some cases. The Technical Standards for Electrical Installations stipulate that electrical equipment with double insulation constructed in accordance with the Electrical Appliance and Material Safety Act may omit grounding work.