Editing Extension cord (section)

==Hazards==
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Fire incident history research has shown that a large proportion of structure fires are caused by extension cords that have been either damaged or overloaded.{{citation needed|date=March 2016}}

The insulation of extension cords, particularly light-duty two-wire cords, is easily damaged by being pinched, crushed, or abraded. The cords can also be damaged at the plug and socket connections by being pulled on excessively, which sometimes happens when people trip on them. Overloading can cause an extension cord to heat up to the point that its insulation either melts or carbonizes. Heating appliances may also cause heat damage to the insulation of a cord, melting or burning it away.

If the internal metal wires are damaged, such as by the cord being crushed in a door, then where the unbroken part of the wires is narrower than the bulk of the wires, this can form a point of high resistance. A hot spot may develop as the resistance of the narrower part of the wire is higher than the rest of the wire, and thus tends to concentrate power dissipation there.

Animals may chew on the wires and remove some of the insulation.  In any of these cases if the damage is not noticed and the cord is not repaired or taken out of service, the damage can lead to arcing or a short circuit between the wires, which can ignite nearby materials.  The exposed wires of an extension cord with damaged insulation can also present a shock hazard to people and animals.