If the question refers to "flexible cords and cables", then Art. 400 would be the controlling NEC rules. Specifically, Art. 400-7 Uses permitted and 400-8 Uses Not Permitted. "Standard" extension cords are used in our homes to "extend" the receptacle power to a more convenient location for power usage, and on construction sites for the same reason. However, all are supposed to be temporary as sparky says "nothing permanent".
