Stranded conductors are composed of multiple uninsulated wires twisted together, providing increased flexibility over a single solid wire. They can be manufactured in various configurations, with the most common being concentric stranding, where wires are arranged in concentric layers around a central wire. Bunched stranding gathers wires randomly, while unilay concentric arranges wires in concentric layers with the same lay direction and length. Aluminum conductor steel-reinforced cable (ACSR) uses aluminum for its outer strands for conductivity and weight, and a steel core for additional strength.

1. Conductor Stranding
Stranded conductors are composed of uninsulated “strands” of wire twisted together. The
advantages of conductor stranding over a single strand of equal cross-section are increased
flexibility and flex-fatigue life. Stranded conductor can be manufactured in a variety of
configurations, the most common being concentric (true concentric, equilay concentric,
unidirectional concentric, and unilay concentric), bunched and rope.
Concentric When the term “concentric stranding” is used, it refers to the definition of the
word “concentric”, which is having a “common center”. Concentric conductor may be defined
as: a central wire (strand) surrounded by one or more layers of helically laid wires in a
geometric pattern. Concentric – or True Concentric characterized by a central wire surrounded
by one or more layers of helically laid wires in a geometric pattern, with alternately reversed
lay direction and increasing lay length.
Lecture Notes by Dr.R.M.Larik 1

2. • Unilay – or Unidirectional Equilay Concentric characterized by a
central wire surrounded by one or more layers of helically laid wires
in a geometric pattern, with the same lay direction and the same lay
length.
Bunched Stranding – Bunch strand wire contains any number of strands in random pattern. Twisted in
one operation, all strands have the same lay direction and same lay length, however, the result is a
rougher surface and lower dimensional tolerance than the concentric constructions. The number of
strands is determined by the size of the individual strands and the total cross-sectional area required
.
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3. Types of Stranding
Bunched: Strands are gathered together with no particular design or arrangement. ...
Concentric: Strands are arranged in a circular pattern. ...
Unilay: Strands are arranged in a circular pattern, but all layers are twisted in the same
direction and share the same lay length.
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4. Aerial bundled cable (ABC)
• Aerial bundled cables (also aerial bundled conductors or simply ABC) are overhead power lines using
several insulated phase conductors bundled tightly together, usually with a bare neutral conductor.
This contrasts with the traditional practice of using uninsulated conductors separated by air gaps.
This variation of overhead power lines utilizes the same principles as bundled conductors, except that
they are closer together to the point of touching but each conductor is surrounded by an insulating
layer (except for the neutral line).
• K-Electric first introduced Aerial Bundled Cabling, in Gulshan-e-Iqbal area of Karachi city with a pilot
project was completed in march 2014. Following 90% theft loss reduction, the decision to roll out the
new cabling across the entire K-Electric distribution network of Karachi.
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5. Advantages of ABC
• Relative immunity to short circuits caused by external forces (wind, fallen branches), unless they abrade the
insulation.
• Can stand in close proximity to trees/buildings and will not generate sparks if touched.
• Little to no tree trimming necessary
• Simpler installation, as crossbars and insulators are not required.
• Ease of erection and stringing, less labor intensive, less construction resources needed.
• More aesthetically appealing.
• Can be installed in a narrower right-of-way.
• At junction poles, insulating bridging wires are needed to connect non-insulated wires at either side. ABC
can dispense with one of these splices.
• Less risk of a neutral-only break from tree or vehicle damage, increasing safety with TNC-s systems.
• Significantly improved safety for linespersons, particularly when working on live conductors.
• Electricity theft is made harder, and more obvious to detect.
• Less required maintenance and necessary inspections of lines.
• Improved reliability in comparison with both bare conductor overhead systems and underground systems.
Insulated conductors prevent accidental contact and supply can be maintained temporarily in the event of a
suspension system collapse.
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6. Disadvantages (ABC)
• Additional cost for the cable itself.
• Insulation degrades due to sun exposure, though the critical
insulation between the wires is somewhat shielded from the sun.
• Shorter spans and more poles due to increased weight.
• Can lead to much longer repair times for installations in hilly areas
due to much higher line weights requiring bigger and more
specialized equipment to repair.
• Older installations are known to cause fires in areas where falling
large trees or branches regularly cause breaks in lines and or in
insulation leading to short circuits which can then lead to burning
insulation dripping to ground and starting ground fires.
• Failure modes through punctures, electrical tracking, and erosion.
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7. ACSR
Aluminium conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength
stranded conductor typically used in overhead power lines. The outer strands are high-
purity aluminium, chosen for its good conductivity, low weight and low cost. The center strand
is steel for additional strength to help support the weight of the conductor. Steel is higher strength
than aluminium which allows for increased mechanical tension to be applied on the conductor.
Steel also has lower elastic and inelastic deformation (permanent elongation) due to mechanical
loading (e.g. wind and ice) as well as a lower coefficient of thermal expansion under current loading.
These properties allow ACSR to sag significantly less than all-aluminium conductors. Per the
International Electrotechnical Commission (IEC) and The CSA Group (formerly the Canadian
Standards Association or CSA) naming convention, ACSR is designated A1/S1A.[1]
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