Publication: Electrical World
New York, NY, United States
PORCELAIN STRAIN INSULATOR.
There are many conditions for which properly designed porcelain strain insulators are well suited. They are largely used in guy wires by street-railway and electric-supply companies. Groups in series are used at dead-ends to take the strain of and to insulate the line wires. The type of strain insulator here shown is made of porcelain said to possess excellent mechanical and electrical properties for the purpose. The glaze is a dark brown, so that the insulators do not readily attract attention in the air. Sharp corners that would he apt to chip have been avoided and the shape of the grooves is such that the wires lie naturally in them. The breakdown emf when the insulators are dry is about 20,000 volts. The approximate ultimate tensile strengths of the insulators, when wired up in guy wires, are, respectively, 14,000 lb., 16,000 lb. and 23,000 lb. for insulators having maximum dimensions of 3 1/8 in., 3 1/2 in. and 5 1/4 in.
Even if an insulator fails either because of excessive stress or through an accident the wires that it carries cannot drop because they are interlinked. Two insulators are often installed in series so that if one breaks the other provides insulation, it being very improbable that two will break at the same time. This type of insulator is made by the Westinghouse Electric & Manufacturing Company, Pittsburgh, Pa.