Southwire C7 Quick start guide

Page 1 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Guide for Installation and Use of Southwire C7
Overhead Conductor
Introduction
Southwire’s C7overhead conductor continues a Southwire tradition of overhead conductors
designed with durability and reliability as the first priorities. Southwire’s HS285 overhead
conductor introduced an ultra-high-strength steel core as a means to improve the sag
performance of conductors with steel cores. Southwire’s C7conductor family is similarly
targeted at high reliability and long service life.
Similar to the case with steel cores, individual carbon fiber composite strands are assembled to
offer a core that is more flexible than a large monolithic core. A multi-strand core has the
significant advantage of structural redundancy which protects the conductor from catastrophic
failure.
C7overhead conductor can be manufactured with a choice of two types of electrical grade
aluminum. C7conductor is available with fully-annealed 1350 O-temper electrical-grade
aluminum. This conductor is designated Aluminum Conductor Composite Supported (ACCS).
ACCS is the best choice for minimizing thermal sag, but may not be suitable for districts with
heavy ice and/or storm loads. C7conductor is also available with ZTAL high-temperature
aluminum-zirconium alloy. This conductor is designated as (Z) Thermal Aluminum Alloy
Conductor Composite Reinforced (ZTACCR). ZTACCR has additional strength and elastic
modulus from the aluminum alloy for handling heavy loads with minimal sag.
C7conductor was designed with the crew in mind. Familiar tools, fittings and procedures
ensure that crews can be confident in the safety and reliability of the C7conductor family. C7
conductor is tough. The multi-strand core brings flexibility and avoids a single-point-of-failure.
C7core is stronger than any steel core and only 20% of the weight. The polymers used in C7
core strands are used in the most demanding aerospace and chemical industry applications.
We can be confident that even chemically-aggressive outdoor environments will not degrade
the polymers in the C7core.
It is, however, necessary to recognize that carbon fiber polymer composites are different from
metals and may require different handling. The following section contains all of the handling

Page 2 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
requirements to ensure the installation is trouble-free. Proper installation will ensure a long
service life for the conductor.
Special Precautions
The C7carbon fiber composite core is stronger than even Southwire’s ultra-high-strength steel
core, HS285. Linear composites like the C7core achieve their superior properties by orienting
the strength members, in this case carbon fiber strands, in the same direction as the
mechanical load. A steel core strand is strong when loaded in any direction; therefore, it can
resist incidental compression and crushing loads during handling and installation. In tension,
the C7core is almost 50% stronger than standard steel core. It is also one-fifth of the weight of
steel.
Polymer composites do not match the hardness and abuse tolerance associated with steel. A
steel core will bend, whereas a composite will resist bending up to the breaking point. Steel is
hard, and resists crushing forces much better than a polymer composite. Fortunately, the
aluminum outer shell protects the core strands during normal bending and crushing. Common-
sense precautions are needed to prevent damage. Handling damage severe enough to damage
the core will leave its mark on the aluminum strands, making damage easy to detect should it
occur. Two failure modes and the countermeasures are discussed below:
1) Excessive bending: a steel strand will kink if it is bent, but it can be straightened with
only moderate loss of strength. Each C7core is tested at the factory to ensure it can
tolerate bending down to an approximately 20 in diameter circle. Unlike steel strands,
C7strands do not yield or kink when bent past a safe diameter. They reach a limit, and
then break. The goal during all handling and installation is to keep a safe margin to the
breaking point. Handling incidents are largely unavoidable; the most important safety
measure is to detect and report any event where the bending limit could have been
exceeded.
To ensure a safe margin to any damage threshold, Southwire recommends a finished
conductor be placed on a reel with a drum diameter greater than 30 times the
conductor diameter. The entrance block and any running angles should use a block with
a bottom groove diameter of at least 30x the conductor diameter. For turning angles
less than 20°, the sheave bottom groove diameter must be at least 20 times the
conductor diameter. On tangent structures, a sheave bottom groove diameter of 20x
the conductor diameter minus 4 in (10 cm), is acceptable.

Page 3 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 1: Example of a situation where bending is excessive even for ACSR. In this case, the
payout reel is located downslope from the bull wheel, and the conductor bending angle is 35°
around a four (4) inch roller. Photo courtesy of Trans Power New Zealand.

Page 4 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 2: A full-size block should be used to avoid excessive bending around small guide rollers.
Photo courtesy of Trans Power New Zealand.

Page 5 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 3: Pulling the conductor to ground to install the traveling ground is commonly done
using a single rope. This could kink the conductor if tension was high enough. Use a 20x
diameter (51 cm) guide roller, or slacken the conductor if it needs to be lowered to install the
traveling ground. Photo courtesy of CenterPoint Energy.
Figure 4: It is OK to drape slack conductor across a small roller. This would not be acceptable if
the conductor was under tension or if the crew was pulling the tail to install a fitting.

Page 6 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 5: Care should be taken to ensure grips do not bend the conductor. Notice, the tail from
the grip is trained at a gentle angle, and tension on the slack side is low to prevent excessive
bending.
Figure 6: If the conductor has taken a “set” from bending, the bent section should be cut out
and a full tension splice installed. The section shown was bent 90° around a six (6) inch radius.
The tensile test showed a 25% strength reduction.
2) Crushing: steel strands are hard and can resist crushing loads. The resins used in C7
conductor are among the toughest available. They can tolerate some abuse, but the
resin is softer than hard aluminum strands and if the conductor is crushed, the core can
sustain damage. Driving a vehicle across a conductor is an example of abuse that a steel
core conductor might survive but will damage a composite core. Similar to the case for

Page 7 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
exceeding the bending limits, external damage to the aluminum strands should be
visible upon inspection. Damaged sections should be cut out and a full-tension splice
installed. Consider sending potentially damaged sections to Southwire for evaluation.
Prior to sagging, the full length of the line should be inspected for any signs of localized
bending. Any kink or birdcage must be evaluated. If in doubt, take a photograph and e-mail it
to Southwire for evaluation. Handling accidents during transmission line construction are
almost unavoidable. What is critical is that damage get reported and repaired before the line is
pulled up to sag.
Protected against excessive bending and protected from crushing, C7conductor will outlast a
steel core conductor for the reason that steel will eventually corrode, whereas the composite
core is immune to all known chemicals in the natural environment. C7 conductor can be
installed using conventional techniques developed over the past 100 years of conductor
installation. IEEE 524, Guide to the Installation of Overhead Transmission Line Conductors, is an
excellent guide and is endorsed by Southwire for both conventional conductors and C7
conductor installation practices. Southwire’s installation guides are reviewed to ensure they
are compatible with the guidelines in IEEE 524.
Reel Handling and Storage
Unloading equipment must never come in contact with the conductor. Lifting must be
performed using a fork lift or crane as described below.
When using a fork lift, the forks shall be placed under both flanges, with the flange facing the
operator.
Figure 7: Forklift handling of reels.
When using a crane, a spreader bar must be used in conjunction with either “J” hooks or an
axle to prevent damage to the reel flange and conductor. “J” hooks should be placed in the
arbor holes. Axles should be inserted through the arbor holes and lifted with straps.

Page 8 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 8: Crane handling of reels.
Reels should be stored away from physical and environmental hazards, such as chemicals.
Conductor reels must be stored standing on their flanges in a flat, well-drained area. The
conductor must not be allowed to touch the ground.
Conductor Handling
Avoid scuffing the surface of C7conductor. C7conductor should not be dragged across any
surface. Minor abrasions should not be a cause of concern; most can be sanded or buffed out.
In an EHV or UHV application, the abrasion should be evaluated for possible corona concerns.
Payoff
The conductor reel should be set up on a reel payoff stationed a minimum of 40-50 feet behind
and in line with the bullwheel tensioner. This will ensure that the conductor does not scrub the
flanges as it is being unwound.

Page 9 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Figure 9: Payoff and bullwheel setup.
Paying off straight from the reel will help to avoid scuffing of the conductor against adjacent
conductor turns or against the reel flange. Proper adjustment of the fairlead roller guides is
necessary to prevent scuffing of the conductor as it reeves through the bullwheel. Reels are
designed only to transport the conductor; they are not designed for use as tensioning devices.
Minimal braking tension should be applied to the payoff to prevent damage to the conductor or
reel. Only enough braking tension should be applied to the reel to keep the conductor taut
between the reel payoff and tensioner and to prevent the reel from over-rotating when the
pulling operation stops. Back tension should not exceed 1000 lb (4.4 kN). If too much back
tension is applied, the conductor on the outer layer can “pull down” into the underlying layers,
as in Figure 10.
Figure 10: Conductor pulldown.

Page 10 of 23 Guide for Installation and use of Southwire C7Overhead Conductor
Bullwheel
Only dual drum multi-groove bullwheel tensioners are recommended for C7conductor. The
bullwheel drums may be offset or tilted so that the offset will be approximately one-half the
groove spacing.
Figure 11: Dual drum bullwheel, courtesy of ONCOR Power Delivery.
Semicircular grooves with depths of 0.5 or more times the conductor diameter and flare angles
of 5-15° from vertical are recommended. For multilayer conductors, the number of grooves in
the bullwheel must be sufficient to prevent the outer layer of wires from slipping through
underlying layers. The minimum bottom groove diameter of the bullwheel must be 35 times
the conductor diameter. Additional sizing charts and diagrams can be found in IEEE Standard
524. Bullwheels must be properly sized and lined to prevent scuffing and damaging of the
conductor.
The outer layer of wires on all standard stranded bare overhead aluminum conductors has a
right-hand direction of lay. The conductor should be reeved through the bullwheels such that,
when facing in the direction of puller, the conductor will enter the bullwheel on the left side
and exit from the right. This orientation is necessary to avoid any tendency to loosen the outer
layer of strands.
Elastomer- or thermoplastic polymer-lined grooves are recommended to avoid permanent
scuffing of the surface of the conductor. Semiconducting linings should not be relied on for
grounding purposes.
The bullwheel should be set up in line with the pull and 3-4 times as far from the base of the
structure as the height of the entrance block at the first structure. This orientation will provide
between a 14-19° angle as the conductor exits the bullwheel and also as it enters the entrance
or breakover sheave.