The advent of electricity market deregulation, the increased operating and overload temperatures of transmission line conductors have caused concern among TSOs (Transmission System Operators) and DSOs (Distribution System Operators) about the effect of elevated temperatures on conventional bare conductors of existing line. Nowadays building new lines is very difficult cause of increased costs to obtain rights of way, public intervention, etc.... Cost and lead times required to place new lines into service are now increased and the business in electric market is reduced for the limited possibility of transmission. Therefore, utilities are attempting to gain as much capacity as possible modifying operation on existing lines. In the past, utilities have been conservative in rating their lines; today the uncertainties in parameters which influence conductor temperature, with a better understanding of environmental conditions and improvements in monitoring instruments and sophisticated analysis tools, utilities are rating lines at higher temperatures with higher level of confidence than in the past. In this paper will be discussed the effects of high temperature plastic creep elongation on the sags and tensions for a conventional conductor. Using equations developed by IEEE Std. the predicted creep for a conductor under high temperature operation can be calculated. The aim of this paper is to provide general recommendations to maintain adequate ground clearance for the safe operation of a line; itpsilas possible to operate at a higher temperature if the associated negative effects are adequately understood, considered and managed.