Editing Extension cord (section)

==Safety==
Cords running across the floor should be covered with a suitable device to protect them from physical damage. However, they should never be covered with a rug or carpet, as this can produce a serious fire hazard.<ref name="auto">{{cite web |url=http://www.esfi.org/resource/extension-cord-safety-tips-478 |title = Extension Cord Safety Tips - Electrical Safety Foundation International| date=6 January 2020 }}</ref>

To avoid the need for rolling-up excess length, using an extension reel or for cutting the cord to size, extension cords are sold in prefabricated lengths of {{Convert|1 to 150|ft}}. Every foot of cord increases the electrical resistance, in turn decreasing the power the cord can deliver. Therefore, the longer the cord, the larger the diameter of the conductors needed to minimise voltage drop (wire gauge numbers are smaller for larger diameter wire). Because of this, it is best to use a cord that's exactly as long as needed and no more.

An extension reel can only carry full rated current when completely extended. This is because the portion of cord on the reel is not exposed to air causing the [[Electric power transmission#Losses|loss power]], (the result of its [[Joule heating|series resistance]]), not to dissipate. An extension cord that is in use while coiled up or coiled in a reel can be a serious shock and fire hazard. The heat produced from the resistance cannot dissipate and is instead trapped between the tightly coiled cable, leading to the a fire or shock.<ref>{{Cite web|url=https://shedheads.net/extension-cord-buyer-guide/|title=Selecting Best Extension Cord for Every Situation|first=James|last=Kennedy|date=May 6, 2017}}</ref> Additionally, the ESFI recommends to never use an extension cord that is covered by a rug or blanket, or that is run through a ceiling or wall, since the heat may not be able to dissipate appropriately.<ref name="auto"/>