Some Insulator Designs Require Special Features to Insure Radio Quietness

The suggested requirements for radio-free pin-type, switch and bus, and suspension insulators, if acceptable, indicate and justify from a factory testing and production viewpoint, the following conclusions as regards existing standard designs: 1. For distribution voltages up to 4,400 or even 5,500 volts, the small one-piece pin-type insulators used require no ``radio-proofing´´, even on solidly grounded pins. 2. If there is 6 to 12 inches of crossarm in series with small one-piece pin-type insulators on low-voltage distribution lines up to 13 kv, no ``radio-proofing´´ is needed on the insulators. 3. Standard untreated pin-type insulators used on 17 to 69-kv distribution and transmission lines have radio noise-influence voltages in the order of several thousand microvolts at a test potential about ten per cent above the usual line-to-ground voltages. ``Radio-proofed´´ pin-type insulators, readily meeting reasonable requirements for freedom from radio interference, are available for use on lines in this voltage range. 4. Standard cemented pin-and-cap switch and bus insulators up to the 69-kv rating, with the exception of the 66-S-class, readily meet the suggested requirements for freedom from radio interference without any special ``radio-proofing´´ treatment; they are inherently quiet. 5. Standard switch and bus insulators for the 66-S-class and the 115-kv and higher-voltage classes may require ``radio-proofing´´ or other precautions to meet the suggested abnormally low requirements. These insulators with slight changes can be made to meet these requirements readily. 6.