Publication: The Journal of Electricity, Power and Gas
San Francisco, CA, United States
THE ROOF INSULATION OF 15,000-VOLT LINES.
A method of taking high tension line wires into and out of station buildings which possesses striking novelty if not boldness has been in use in the Los Angeles substation of the San Gabriel Electric Company with absolutely perfect success for upwards of two years. The device is due to Mr. E. A. Beck, superintendent of the company named, and so satisfactory has it proven that it is being adopted in all the high tension distribution work of the company, until there are something over one hundred of these "roof insulators" in use in the power plants, substations and pumping stations of the San Gabriel system. The pressures insulated by the device range from 2400 volts to 15,000 volts, in fact, all the high tension transmission and distribution lines are, or are fast becoming, so insulated.
The form of construction of the roof insulator is the same whether it is to be used in 2400-volt or 15,000-volt service. The conductor which is always of No. 6 B. & S. gauge, is encased in 15,000-volt, solid rubber insulation, over which is drawn selected soft white rubber hose. Then this is encased in a good quality of three-quarter inch garden hose, the whole being threaded through a special inside porcelain bushing having a length of eighteen inches, an outside diameter of one and three-quarter inches and an inside diameter of one and one-quarter inches. Next, this eighteen-inch bushing is sulphur-cemented (the cement wall being one-quarter inch in thickness) into a special white porcelain bushing measuring eight inches in length by two and one-quarter inches inside diameter. The cap is then knocked off a glass insulator (No. 1 Provo type) and the heavily insulated conductor is passed up through it in the manner shown in the adjoining illustration, after which it is carefully taped and P. & B. painted, especially at the point of passing through the insulator top and at the ends of the special insulation. Care must be taken to see that the additional insulation of white rubber and selected garden hose make a snug fit, one over the other. The outside diameter of the three-quarter inch rubber hose must be larger than the pin clearance of insulator, so that the insulator has to be screwed down over hose until the eighteen-inch bushing enters the inner petticoat of the insulator, when the two are sulphured together by pouring sulphur into the inner petticoat of the insulator and around the top of the eighteen-inch porcelain bushing, making the whole one rigid piece. After being placed vertically in a board having the pitch of the roof it is then ready for use, and the experience of the San Gabriel Electric Company is that it may be relied upon as being both moisture proof and puncture proof.