Similarly, covering a cord with a rug or pillow can trap heat and overheat the cord. This trapped heat can damage the cord and lead to a fire. Altering a cord in any way can also lead to safety hazards. A common mistake is altering the third wire grounding lug. Appliances that utilize the third lug for grounding should be used only with an extension cord that includes the third wire ground.
Plug adapters void the safety provided by the third grounding wire.
As we enter the heating season, now is a good time to take an inventory of the capacity and condition of your extension cords. Look for cords that may be overloaded by the connected appliance. Look for signs of age and cracking in the insulation. Look for plugs or receptacles that have worn and no longer make a firm connection. When in doubt, replace the cord.