Metal insulator pin being used on 33,000 volt line in California

THE METAL INSULATOR PIN.

Insulator pins are usually made of wood, but the metal pin is coming into use, having been adopted on the 33,000-volt double circuit eighty-three-mile transmission line at Los Angeles, Cal. The metal pin has many advantages over the wooden pin. To secure sufficient strength in the shank the diameter of the wooden pin must be large, which necessarily increases the size of the cross-arm. The wooden pin. is simply driven into the cross-arm, whereas the metal pin is bolted thereto, so that the line wire cannot raise or pull the pin out of the cross-arm. This frequently happens with wooden pins, and to prevent it a nail has to be driven through the cross-arm into the pin shank, thereby weakening both. The use of a wooden pin is justified only by low cost and its insulating quality. As for the latter, dependence should not be placed upon a pin for insulation, which should be fully given by the insulator. One of the leading engineers of the Pacific coast recently said: "Wooden pins are subject to so many uncertainties where used in connection with very high voltages, especially where the air contains salt, smoke or dust, that it seems desirable to abandon their use for such purposes, wherever possible, and to substitute a metallic pin. For a metallic pin a l-inch diameter round milled steel bar, with a shoulder and shank cast upon it, is recommended. This will not snap off under strain or shock as a cast iron pin might do, but will only bend under severe strain and thus still support the insulator and line safely.