Power Insulators
by Robert Winkler

Reprinted from "INSULATORS - Crown Jewels of the Wire",, October 1970, page 19

I am taking this information from the Northern Indiana Public Service Company that serves our area. Although this is local information, I believe it generally holds true across the country.

At this time NIPSCO still has a large number of glass insulators in service mostly in the lower voltage distribution systems. However, about two years ago they began to stop using glass entirely, and all new lines and replacements are now using porcelain.

The list below gives the types in present use according to size and insulating capacity. All are porcelain, but I have seen about every one at one time or another in clear or carnival Pyrex glass.

1. SPOOL INSULATORS - This type is generally used for lower voltages (120/240 to house service) and is often used as a deadend. It is also used in lightning arrester systems and to carry secondary, neutral or ground lines in distribution systems. Glazes are usually brown or white. All new insulator whether they are spools or pintype, are now glazed light gray, generally, for the sake of appearance.

2. SIGNAL - This insulator seems to be used less and less here. They have been used on low voltage distribution circuits, in street lighting circuits and to carry the secondary line in earlier distribution systems. Glazes - brown, reds, grays, white.

3. SADDLE TOP (11 KV INSULATORS) - This type is and has been very popular in the distribution systems. It has a wide range of shapes, colors and sizes. Glazes, blue, browns, reds, white, green, grays and two-tone variations.

4. 23 KV INSULATORS - These are not as popular as they used to be. At one time some versions were designed more like an 11 KV saddle top with a wide base and an additional inner skirt or two. Other early models were two parts cemented together. Most of the newer ones have a metal insert to fit the steel pins. Glazes are usually brown, some reds.

5. 4S KV INSULATORS - This is the standard transmission circuit insulator usually about a foot high. Older ones were two or three parts cemented together, and they weren't quite so heavy as the newer types. Glazes are browns, reds, occasionally light blue, and I have heard of white.

6. 69 KV INSULATORS - These are the biggest pin type insulators I know of. They are cemented together in three sections and have a metal clamp for the wire. I would estimate them to be about 2 feet high and almost as wide. I have only seen these in brown glaze.

7. SUSPENSION STRAIN - This type is used on wood or steel towers for 69 KV and up. The more on a chain, the more insulating capacity is obtained. This type is commonly called the "bell type" and is also used to dead end lines. Glazes are usually brown, reddish or light blue.

8. SUSPENSION STRAIN - (Fog type) - This final type is used for lower voltages, such as 7,200 volts, or a distribution circuit. While the bell type gives best insulation hanging vertically, the fog type is designed for dead ends which are more horizontal. This is a fairly recent type, but is becoming quite popular. Glazes are brown, reds.