Multipart Porcelain Insulators
Left to right: M-2254 "LIMA, N.Y.", M-2260B "NEW LEXINGTON, O.",
and M-2260 N-N Thomas
Early classic porcelain insulators are those generally produced before 1920. During this early time period, little was known about electrical properties of high voltage multipart porcelain insulators and potential problems with cement expansion which often lead to damaged insulators. One characteristic of these first porcelain insulators is the frequent use of upwardly curved middle or bottom shell. This feature is referred to as the "lily-shell" design. Thomas popularized this design feature.
Before about 1918, insulator manufacturers knew little about designing insulators to withstand the electrical strain of high voltage. They often merely followed the whims and desires of the customer. Electrical transmission voltages increased at a rapid pace from 1900-1920. It wasn't until a number of lines experienced abnormal insulator failures from broken porcelain lead manufacturers to study the problem. They discovered that the Portland cement used to assemble the insulators expanded much greater than the porcelain resulting in a force that cracked and often shattered the insulator. A number of patents starting with the Fortescue and Gilchrest patent of 1921 reduced the damaging effects of cement.
These web pages will give you but a glimpse at some of the rare early classic porcelain insulators. It is merely a sampling of the five major manufactures which produced porcelain insulators for high voltage service. Additional information may be found by reading the following excellent books:
Collector's Guide for Porcelain Insulators by Elton Gish
Multipart Porcelain Insulators (second edition, 2000) by Elton Gish
This book has been completely rewritten and 227 new styles have been added to the M-Chart. It is a complete reference for markings, manufacturer and power line histories, and contains many historical photographs that have never been published before.
Fred M. Locke: A Biography by Elton Gish
Value Guide for Unipart and Multipart Porcelain Insulators 2nd edition by Elton Gish