Extension cords can be broadly divided into two types: indoor use in offices, etc., and outdoor use in factories, construction sites, exhibition halls, etc. The voltage is 100 V or 200 V, and you need to pay attention to the shape of whether it is 20 A dual purpose, 2P or 3P plug, and A2 or A3 socket, etc. For outdoor cords, such as cords made of VCT material with excellent durability and cold resistance, rainproof type plugs to prevent electric shock and leakage due to rainwater, etc. the design makes it so they are not impacted by the environment. In addition, for indoor cords, there are extension cords that take safety into consideration, such as a retaining function to prevent the plug from falling off, plugs using a flame retardant material, plugs with an insulating cap to prevent tracking fire, etc.