Electrical Engineering

Are you refering to high voltage, line insulators? Being glass and this color comes from years past, long before most of us were even a glint in someone elses eyes.

DC voltage has a "direct", or rather, "constant" feed for testing circuits for shorts and open lines. AC voltage has a lag, and is not a constant source. AC voltage is actually a percentage of usable energy, it fluctuates and does not remain constant enough for precissionn testing. Hence forth, we use DC voltage with a known current applied, and we know what the actual calculated product should be.

Hope this was a reasonable answer for your delight. 8>) Maximo

Brown (actually chocolate) glazed wet process porcelain insulators was standard for many years. The primary reason was the contrast between the glaze and the white fired porcelain. Made it easier to judge glaze coverage and see surface and sub-surface defects. The glaze on porcelain insulators is actually a compression glaze that applies a compression stress on the porcelain surface during firing. Porcelain is, of course very strong in compression but weak in tension.

In the U.S. during the Johnson presidency, Mrs. Johnson became involved with beautification programs and environmental groups that pushed for a more beautiful outdoor environment which included overhead transmission lines, equipment, insulators, conductors, etc. The industry response included a conversion to gray (actually ANSI-70; skytone) glazed porcelain insulators. Thus most porcelain insulators today are ANSI-70.

In fact, porcelain insulators have always had a variety of glaze colors for several reasons; including different colors to define strength ratings, specific applications, etc. Thus, you will frequently find suspension insulators with light blue, royal blue, green, red and even yellow glaze.