Tips & News - Jan. 2016

Four years, several prototypes and thousand of installations later, the new neutral clevis design is complete.

Over time, the weight of ice on the neutral caused the tie wires to stretch and the upset bolt to bend. When this happened, the neutral could come in contact with the bottom steel leg of the clevis. Moved by the wind, it would rub against the sharp edge of the clevis. It was not unusual for line mechanics to be called out, only to find the neutral had been worn through and was lying on the ground. In the northern part of Alliant Energy’s territory, where galloping lines are not uncommon, roughly 90% of the neutrals had damage from being pulled down and rubbing against the edge of the clevis. Horizontally oriented neutral clevises were hard to find, so we focused on finding a stronger upset bolt. At that time, spool insulators were designed to fit over a standard 5/8" upset bolt. We wanted to upgrade to a 3/4” bolt, but it was not a simple thing to do. It was not until 2008 that we found a spool that would fit over a 3/4" bolt, which were not available. So, from 2009 to 2001, we purchased 1,665 custom fabricated, 3/4" upset bolts. This was a workable solution, but the cost was high since upset bolts had to be specially made. Also, to accommodate different pole diameters we had to purchase three different length upset bolts. It was not a satisfactory solution and we began looking for a better clevis. In April of 2011, we found a clevis that could be mounted horizontally, but the legs were straight and when you inserted the threaded pin it would dig into the pole.

BROKEN NEUTRALS Alliant Energy identified the need for a better neutral clevis more than a decade ago. Our distribution system has an under-hung neutral and some neutral conductors were attached to poles with a vertically mounted clevises. In other words, the neutral was held to the side of the vertically-oriented, spool insulator by a steel tie wire. In other parts of the country, this is considered standard practice and does not cause any problems, but within certain parts of Alliant Energy’s service territory, it was an issue. Repeated wind and ice loading damaged the neutral wire.

FIGURE 1 - The starting point. The old style, vertically mounted clevis (shown without insulating spool). If the tie wire stretches, the neutral can fall down, against the bottom leg of the clevis.

FIGURE 2 - The final design. The spool is horizontal. It has an offset leg, upset pin (not bolt), large cotter pin, and ‘finger’ to temporarily hold the neutral conductor during installation.


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