USA difference of opinion on porcelain vs. glass

Insulators and Pins used in the Western States.—According to the Electrical World of New York, there is a decided difference of opinion as to the relative advantages of porcelain and glass for high-tension insulators. The advocates of porcelain point to the fact that it is much stronger mechanically than glass, and that it may be shot at and chipped without cracking the whole insulator to make a leak. The advocates of glass urge its cheapness as one point in its favour and also its dielectric strength. They claim that porcelain must necessarily depend, to a large extent, on the strength of the outer coating or glaze for its insulating qualities, and if this becomes cracked by moisture working in will cause a puncture of the insulator in time. This was no doubt true with the first porcelain insulators built, but on recent work there appears to be little practical difference in the working of porcelain and glass. At Provo with 40,000 volts and a grounded neutral, glass insulators are used. That the leakage towards ground must be considerable on this line is shown by the fact that it is impossible to operate a telephone line on the same poles. The tendency for the current to seek ground via the telephone line (oven though the telephone line was not intentionally grounded) was sufficient to burn the poles where it jumped from the poles to the telephone tie wires. On the 33,000 volt line into Los Angeles the neutral is also grounded, but the telephone line is perfectly satisfactory. Porcelain insulators of about the same diameter as the glass used on the Provo line (about are employed on this line, but the voltage not being the same it is hardly fair to compare results. Wooden pins boiled in paraffin or linseed oil are most commonly used, though on the 33,000 volt Los Angeles line, just referred to, iron pins are giving satisfaction.