Bell System Sleet Storm Map

ANY, no doubt, have seen copies of the Bell System Sleet Storm M a p which has been prepared to show the relative intensities and frequencies of sleet storms throughout the United States. In the midst of the current sleet storm season it may be of interest to discuss some of the factors which have led to the preparation of this map, and to outline in a general way, the means by which its indications are utilized in the design, construction and upkeep of the pole and aerial wire plant. A sleet storm to be destructive to telephone plant must be accompanied by such atmospheric conditions as will cause either a relatively heavy deposit of ice with no wind or a deposit of ice with a considerable amount of wind. It is neither difficult nor expensive to construct the aerial plant so that it will withstand winds of relatively high velocities provided the wires are free of sleet. A slight deposit of sleet, however, rapidly increases the "sail a r e a " against which the force of the wind is directed and the resulting load constitutes one of the most formidable and most difficult to anticipate of any of the destructive agencies with which wire using companies have to contend. Maintenance difficulties unfortunately, are not necessarily at an end with a lessening or cessation of the wind, for this change may often increase the precipitation of sleet, which undisturbed by the wind builds up around the wires, frequently stressing them beyond the breaking point. It is not uncommon for a wire of approximately 1 /10 of an inch in diameter to accumulate sleet or ice under favorable atmospheric conditions to the extent of a cylindrical coating from one to two inches or more in diameter.