Transmission Blocks – 78 Series

Transmission-class line construction is very specialized. Structures are taller, spans are longer, conductors are larger/heavier/stiffer, and pulls are longer and can extend over steep and very uneven terrain. In addition, aluminum conductors vary in construction requirements, calling for special handling techniques, tools, and equipment.

Transmission construction also involves different line and structure designs, as well as
different conductor configurations. Some lines are strung using conventional, ground-
based equipment and tools, while others require stringing using helicopters.

The configuration and quality of the blocks in which sheaves are mounted are as important
as the sheaves.

About 78 Series Transmission Blocks
The 78 Series single-conductor stringing blocks are an ideal choice for stringing large-
diameter transmission-class conductor. These blocks are available with 20″, 22″, 28″, 35”,
and 42″ (OD) sheaves, and they are light-weight, yet exceptionally rugged, reliable, and
durable. Their low-friction bearings render high block efficiency, which helps to maximize
stringing distances while minimizing pulling tensions and reducing loads on stringing
equipment. Combined with the associated family of hardware and accessories, the
78 Series affords utilities and their contractors exceptional versatility in how and where
it may be deployed and in the range of installation problems it can help solve.

The 78 Series blocks’ light weight and durability derive from the materials and methods
used to make them. The material used for the frame is “virgin” A356-T6 Aluminum, which
is an aluminum alloy with very tightly controlled proportions of other materials to assure
optimum performance during manufacture and in the field. Virgin material is material
that has not been mixed with scrap material, not even with scrap of what may have once
been the same alloy. That Sherman & Reilly uses “virgin” material assures that the material
is exactly and only the pure and correct alloy, and that it has not been contaminated by
impurities (notably iron) that often accompany non-virgin material.

78 Series frames are cast (molded) as molten metal. The properties and purity of the A356-T6
Aluminum used by Sherman & Reilly assure that the molten metal flows smoothly and evenly
throughout the mold, assuring proper and uniform density throughout the finished frame.
Proper density and uniformity combined with the purity and metallic properties of the alloy
assure that the frame is strong but light-weight, and assure that there are no internal voids or
brittleness that could cause sudden complete failure of the block in the field.

The sheaves of the 78 Series are also made of the same virgin A356-T6 Aluminum as the frame.
They are also similarly cast, but they have the additional manufacturing step of having the grooves
and bearing surfaces machined for smoothness and precision fit. Combined with low-friction,
lubricated-for-life bearings, the sheave materials and how they are made assure high-efficiency
and smooth-stringing performance.

Specifications:

• 20 in, 22 in., 28 in., 35 in., and 42 in. Sheaves
• Conductor guard to minimize risk of lines binding between sheave & frame.
• Available as polished-groove or lined with neoprene or urethane.
• High-strength Aluminum-alloy frames and sheaves.
• High-efficiency bearings, with provision for pressure-lubrication
• Forever Warranty™