You should avoid stringing together more than one extension cord. This can potentially lead to equipment failure, fire, or electrocution. The rating of a power cord is based on its length. If you plug in two identical cords, this will lead to cutting the capacity in half, possibly resulting in overheating and voltage drop. This reduction in power is why most extension cords do not exceed 100ft in length, which could easily happen if you plug in multiple cords. If you need more than this length, you will probably require a temporary power distribution box.