Use of an extension cord can cause a voltage drop that may cause device to a malfunction if the drop is sever enough. If an extension cord must be used, use the shortest length possible to both minimize voltage drops as well as other potential safety hazards. Additionally, use an extension cord that is rated for the load that will be placed upon it. For instance, a portable heater that draws 15 amps should use an extension cord rated for at least 15 amps and preferably a few extra amps as an additional safety margin.
The Consumer Product Safety Commission (CPSC) has issued the following recommendations for the safe use of extension cords.
Use extension cords only when necessary and only on a temporary basis.
Use polarized extension cords with polarized appliances.
Make sure cords do not dangle from the counter or table tops where they can be pulled down or tripped over.
Replace cracked or worn extension cords with new. #16 gauge cords that have the listing, of a nationally-recognized testing laboratory, safety closures, and other safety features.
With cords lacking safety closures, cover any unused outlets with electrical tape or with plastic caps to prevent the chance of a child making contact with the live circuit.
Insert plugs fully so that no part of the prongs are exposed when the extension cord is in use.
When disconnecting cords, pull the plug rather than the cord itself.
Teach children not to play with plugs and outlets.
Use only three-wire extension cords for appliances with three-prong plugs. Never remove the third (round or U-shaped) prong, which is a safety feature designed to reduce the risk of shock and electrocution.
In locations where furniture or beds may be pushed against an extension cord where the cord joins the plug, use a special "angle extension cord," which is specifically designed for use in these instances.
Check the plug and the body of the extension cord while the cord is in use. Noticeable warming of these plastic parts is expected when cords are being used at their maximum rating, however, if the cord feels hot or if there is a softening of the plastic, this is a warning that the plug wires or connections are failing and that the extension cord should be discarded and replaced.
Never use an extension cord while it is coiled or looped. Never cover any part of an extension cord with newspapers, clothing, rugs, or any objects while the cord is in use. Never place an extension cord where it is likely to be damaged by heavy furniture or foot traffic.
Don't use staples or nails to attach extension cords to a baseboard or to another surface. This could damage the cord and present a shock or fire hazard.
Don't overload extension cords by plugging in appliances that draw a total of more watts than the rating of the cord.
Use special, heavy duty extension cords for high wattage appliances such as air conditioners, portable electric heaters, and freezers.
When using outdoor tools and appliances, use only extension cords labeled for outdoor use.