As the transmission infrastructure ages - and as permitting and constructing new facilities become increasingly difficult - pressure to increase the use of existing facilities is mounting. Finding available capacity within current systems has emerged as an issue of prime importance as we are required to move more and more power over existing rights-of-way (R/Ws). The maximum line loading is subject to its "rating." While any one of several variables can govern the rating of a circuit, perhaps the most common limiting factor is the National Electrical Safety Code (NESC)-imposed minimum clearance. As utilities load their transmission lines to higher levels, the conductors heat up, elongate and sag. The real limiting factor, and hence the basis for a line's rating, is often the ability of the utility to maintain a safe clearance between energized conductors and the ground, trees, vehicles and other objects directly below the line, as set forth in regulations such as the NESC.
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