NESC® Requirements (Strength and Loading)

The National Electrical Safety Code (NESC) contains safety rules for the overhead lines, including detailed strength requirements and clearance rules for the support structures and cables or messenger wires. In particular, the strength of the pole, as well as crossarms and various support hardware, must be compatible with the basic loading conditions specified by the NESC, depending upon the grade of construction. For typical joint‐use applications, the required loading condition is that of NESC Rule 250B, corresponding to the storm loads of the geographic districts. The Rule 250B storm loadings vary from ½‐in. radial ice thickness in the Heavy loading district, to ¼‐in. radial ice in the Medium loading district, to the absence of ice in the Light loading district. These ice conditions, furthermore, are to be considered in the presence of wind pressures of 4, 4, and 9 psf, respectively.