Porcelain Insulator News
by Elton Gish, NIA #41
Reprinted from "Crown Jewels of the Wire", August 1987, page 29
Robert Winkler has provided us with many fine drawings of pole line
construction showing insulators and how they were used in different pole
configurations. The drawings were a trademark for the Porcelain News column for
several years. Robert has sent information (with the assistance of Ken Stefan)
regarding the new pin-post insulators. An article on the pin-post from Chris
Hedges appeared in December, 1986 CJ.
Robert said that he first saw these units on a line in Chicago in the Fall of 1978. The first units
observed were all of the Chance
design and were simply marked CHANCE without dates.
In 1983, he found a 3-phase armless line with pin-posts. These looked
different than the Chance types. They were similar to a small multipart with a
narrow skirt tapering towards the top. After Ken went to work for Commonwealth
Edison in Chicago, he was able to obtain one of this style which turned out to
be manufactured by Lapp.
Ken's research determined that the pin-post style was an experimental design
developed jointly by Commonwealth Edison Co. and Lapp in 1975-76. It was to be
used as a contamination insulator on 12.5 kV lines with covered conductors. They
found that certain insulator/conductor tie combinations not only made them more
susceptible to burndowns but also generated radio interference (RI)
The use of pin type insulators with radio-free glaze were eliminated since
they could be inadvertently installed on 12.5 kV bare conductors thus producing
RI noise. The post type insulators can be installed with bare or covered
conductors without RI noise generation but were too expensive for this service. The need was then established for an
inexpensive insulator that could be used on a standard 1-inch steel pin in the
12 kV service. The pin-post met all the required conditions.
There are three pin-post designs and U-numbers have been assigned by Jack
Tod. The original Lapp pin-post design is U-425. The Lapp design had a defect in
that
the narrow tapered skirt would snap off at the top of the pin when it was
over stressed. This problem lead to the Chance version. The Lapp discontinued
their style by 1985. They did make a fairly large run of the U-425 for
Commonwealth Edison Co. These units can be seen today scattered around the
Chicago area installed on lines during 1976-77. C. E. Co. discontinued ordering
the design from Lapp after this period.
The Chance design is U-425A. This style was introduced in 1977 and has a
built-up pin hole shaft which eliminated the failures experienced with the Lapp
design.
According to a recent Commonwealth Edison Co. specification sheet on the
pin-post design, they have three vendors: Lapp (now discontinued), Chance (the
main supplier) and Porcelain Products - Knox (which appears to be the backup or
secondary supplier).
The P. P. - Knox style is U-425B. The first use of U-425B by C. E. Co. was in
1983. Their unit was a little different from the Chance design -- not as bulky
and somewhat better designed and finished. However, Chance came back strong with
a price reduction that P. P. - Knox could not match for the quality of the
product, so Chance is still the major supplier of the pin-post. P. P. - Knox is
maintained as a backup supplier with occasional orders. Their units are marked:
P. P. - KNOX.
In case you are wondering about the P. P. - Knox company, several years ago
(circa 1982) Porcelain Products, Co. purchased the Knox Porcelain Corporation
plant at Knoxville, Tennessee.
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