An extension cord may look harmless but most extension cords are designed to carry 110 volts of electricity and 110 volts can kill. Extension cords are considered by both OSHA and the National Electric Code to be temporary wiring and certain rules apply to their usage. One of the most overlooked of all rules is the requirement to do a visual inspection of the cord before each use.
Extension cords are usually items that get lots of hard usage and are very susceptible to damage. This is one reason that OSHA requires a visual inspection of all flexible cords (including those on power tools) each day or before each use.
To provide an extra layer of protection, extension cords are required to be double-insulated. This means the conductors are covered with a colored insulating material and the jacket is an additional and separate layer of insulation. Never use a flat, appliance-type cord at work; the conductors of this flat cord are molded into the cord material and provide one layer of insulation.
A proper cord inspection includes an examination of the jacket for the entire length of the cord. Look for cuts in the jacket that expose the colors of the inner conductors, Once the integrity of the outer jacket is compromised, the cord cannot be repaired with tape or used in this condition. The cord may be cut and UL approved male and female plugs affixed to the ends. Look for damaged strain relief, loose or missing prongs or ground pin, evidence of heat, such as smoke or melted insulation, pinching or discoloration.
Remove damaged cords from service until repaired or disposed of by a qualified person.
Extension cords are a safe and convenient way of providing power to portable equipment. Make sure that the thickness of the cord is the same, or even larger, than the cord of the tool being powered. You risk overloading the circuit if you plug one extension cord into another.
Never forget to use GFCI protection when using an extension cord. It can save your life!