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 loss power, (the result of its 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. 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.