Although it sometimes seems to be the only solution, attaching two extension cords together is not a good idea. Keep a home safe, and buy a longer extension cord made for your particular purpose.
While stringing together two extension cords can work as a temporary solution, such as in the case of a short power failure, it creates a significant risk when used as a long-term solution. Extended cords reduce the wattage capabilities of each cord and may lead to meltdown and fire.
The Consumer Products Safety Commission says that an estimated 3,300 residential fires each year start as the result of extension cords. The most common problems are overloaded circuits, short circuits, damaged cords and misused cords. Stringing together two cords is an example of a misused cord. About 50 people die and 270 people are injured each year in these fires.
The ideal solution is to avoid using extension cords. Where this is not practical, consider a short cord, insulated power strip with heavy insulation and adequate protection from shorts. If you must use an extension cord, use the shortest one possible for the application. Avoid using extension cords for appliances with a heavy wattage draw such as microwaves or irons.