ACSR and ACCC at a Glance
For more than seven decades, Aluminum Conductor Steel-Reinforced (ACSR) has been the global default for overhead transmission. It is well understood, widely available, and competitively priced. But over the last twenty years a newer family of advanced conductors has begun to reshape how utilities think about capacity, losses, and reconductoring. ACCC — Aluminum Conductor Composite Core — is the most widely deployed of these, with installations across more than 60 countries.
This article compares ACSR and ACCC directly: how they differ in core material and construction, how those differences translate into ampacity, sag, and line-loss performance, what the cost picture looks like over a 30–40 year service life, and when each conductor is the right engineering choice.
ACSR is an overhead conductor built from concentric layers of hard-drawn 1350-H19 aluminum strands wound over a galvanized steel core. The steel carries the mechanical load; the aluminum carries the current. Continuous operating temperature is typically limited to 75–90°C.
ACCC is an overhead conductor built from fully annealed 1350-O aluminum strands — usually in a trapezoidal (TW) shape — wound over a hybrid polymer-fiber composite core (carbon fiber inner, glass fiber outer). The composite core carries the mechanical load; the soft aluminum carries the current. Continuous operating temperature is rated to 180°C, with short-term emergency ratings to 200°C.
The two conductors share the same basic architecture — a load-bearing core surrounded by current-carrying aluminum — but every consequential property follows from what that core is made of. The rest of this article unpacks those consequences.
The Core Difference: Steel vs Polymer Composite
The single design decision that separates ACSR from ACCC is the choice of core material. Everything else — ampacity, sag behavior, line losses, weight, and cost — flows from this one choice. The figure below shows the two conductors side by side at the same overall diameter.
Figure 1. Cross-section comparison at equal overall diameter. ACSR’s round strands cannot pack without leaving interstitial gaps; ACCC’s trapezoidal annealed-aluminum strands fill the space almost completely. Combined with a composite core that is lighter than steel for equivalent mechanical capacity, this is what allows ACCC to carry roughly 28–30% more conductive aluminum in the same diameter.
What the Steel Core Does in ACSR
Hard-drawn aluminum is strong enough to handle current but not strong enough to span tower-to-tower without sagging excessively. The galvanized steel core in ACSR is what takes the tension. Steel has a modulus of elasticity around 200 GPa and a tensile strength of roughly 1,200–1,400 MPa for the grades used in conductor cores, which gives ACSR the mechanical strength needed for spans of several hundred meters. The trade-off is twofold: steel is heavy (density 7.85 g/cm³), and it expands meaningfully when heated (coefficient of thermal expansion around 11.5×10−6/°C).
What the Composite Core Does in ACCC
The ACCC core is a hybrid pultruded rod with a carbon-fiber inner section and a glass-fiber outer sheath, bonded in an epoxy matrix. The carbon fiber provides the high tensile strength — rated tensile values above 2,500 MPa are typical for the core itself. The glass fiber outer layer serves two purposes: it provides electrical isolation between the carbon and the aluminum (preventing galvanic action), and it gives the core flexural durability. The composite has a density around 1.9–2.0 g/cm³ — roughly one-quarter the weight of steel for the same volume — and an axial coefficient of thermal expansion near 1.6×10−6/°C, about seven times lower than steel.
What This Means for Aluminum Content
Because the composite core occupies less cross-sectional area than a steel core of equivalent mechanical capacity, ACCC can fit more aluminum into the same overall diameter. Combined with the use of trapezoidal (TW) strands — which fill space more efficiently than round wires — the result is typically 28–30% more aluminum per unit diameter compared to a conventional ACSR. The aluminum itself is fully annealed 1350-O, the same soft temper used in ACSS, because the composite core will be carrying essentially all the mechanical load.
For context on terminology: ACCC was originally developed by CTC Global, a manufacturer based in California, and the name “ACCC” is the technology designation for this composite-core conductor family. Various manufacturers worldwide supply ACCC and similar composite-core conductors under licensing agreements or comparable proprietary designations.
Performance Compared: Ampacity, Sag, and Line Losses
The “more aluminum, lower-CTE core” combination produces three coupled performance advantages over ACSR: higher ampacity at the same diameter, much lower sag at high temperatures, and reduced I²R losses across all loading conditions. The table below summarizes typical values for two conductors of equivalent overall diameter and span class.
| Parameter | ACSR (Drake equivalent) | ACCC (Drake-size equivalent) |
|---|---|---|
| Aluminum cross-sectional area | ~403 mm² | ~519 mm² (+29%) |
| DC resistance at 20°C | ~0.0718 Ω/km | ~0.0552 Ω/km (−23%) |
| Continuous operating temperature | 75–90°C | 180°C |
| Continuous ampacity (same conditions) | Base | +25 to +50% |
| Coefficient of thermal expansion | ~18×10−6/°C (effective) | ~1.6×10−6/°C (core) |
| Sag at 100°C vs ambient | Significant rise | Very small rise |
| Total conductor weight | Base | Comparable or slightly lower |
| Line losses at equal current loading | Base | 25 to 40% lower |
Values are representative of conductors in the 400–500 mm² aluminum class for like-for-like comparison. Exact figures vary by manufacturer datasheet; engineers should always design from project-specific data.
Ampacity: Why ACCC Carries More Current
Two effects compound. First, the larger aluminum area at the same OD lowers the conductor’s DC resistance, which means less heat is generated per ampere of current. Second, the 180°C continuous temperature rating — more than double ACSR’s typical 90°C ceiling — gives the conductor headroom to operate at higher currents before the thermal limit is reached. In practice, a Drake-size ACCC can carry roughly 25–30% more current than a Drake ACSR under normal conditions, and substantially more under emergency ratings. Independent test data from CIGRE and IEEE has confirmed ampacity gains in this range across multiple commercial deployments.
Sag at Elevated Temperatures
The much lower CTE of the composite core means the ACCC conductor barely expands as it heats up — and what little expansion does occur is almost entirely in the aluminum, which has limited effect on sag because the soft annealed aluminum sheds load to the rigid core, very much like the load-transfer mechanism in ACSS. The figure below shows the sag-temperature behavior of both conductors on the same span, using the coordinate system established in our companion articles on ACSS and HTLS.
Figure 2. Sag versus operating temperature on a representative span. ACSR reaches its continuous operating ceiling at roughly 90°C with sag already up around 1.5× the cold-stringing value. ACCC continues operating to 180°C while sag stays close to 1.3× — the composite core’s very low coefficient of thermal expansion is what keeps the conductor short even at high operating temperatures.
Line Losses: The Argument That Builds Over Time
Resistive (I²R) losses scale with the square of the current and linearly with conductor resistance. A 23% reduction in DC resistance, which is typical for ACCC versus an equivalent ACSR, translates roughly to a 23% reduction in losses at any given current. Over the 30–40 year service life of a transmission line carrying meaningful load, those saved kilowatt-hours add up to a substantial energy and emissions number. For utilities operating under loss-reduction mandates or carbon accounting requirements, this is often the headline argument for ACCC. Our companion article on transmission line power loss calculation works through the I²R loss calculation in detail and shows worked examples for both conductor types.
Cost and Lifecycle Economics
If ACCC outperforms ACSR on ampacity, sag, and losses, why is ACSR still the global default? The honest answer is upfront cost — and a less honest answer is procurement inertia. The cost picture only becomes favorable for ACCC when lifecycle economics are taken into account, and even then the answer depends heavily on loading and electricity prices.
| Cost dimension | ACSR | ACCC |
|---|---|---|
| Conductor material cost per km | Base | Typically 1.8× to 2.5× ACSR |
| Hardware (dead-ends, splices) | Standard, widely stocked | Specialized, manufacturer-specific |
| Installation labor | Standard crews and equipment | Trained crews, certified equipment |
| Annual I²R loss cost | Base | ~25 to 40% lower |
| Tower / structure modifications for reconductoring | Often required if uprating ampacity | Frequently avoidable due to low high-temp sag |
| Service life | 40–60 years (well-documented) | ~40 years projected (newer technology) |
The CapEx gap is real and not small. A Drake-equivalent ACCC will cost roughly twice as much per kilometer of conductor as a Drake ACSR at the factory gate, and the specialized hardware adds further cost. Installation also requires trained crews and certified stringing equipment, which can be a barrier in markets where ACCC has not yet built up a local supply and skills base.
Where ACCC pays back is on the operations side. The lower resistance and the absence of high-temperature sag derating mean the conductor carries more energy, more cheaply, for longer — and a reconductoring project that would have required tower replacement with ACSR can often be done on existing structures with ACCC, which is a very large cost line that disappears from the project budget. Whether the math works depends on three variables: the line’s annual loading factor, the local cost of electricity (which sets the value of the saved losses), and whether the alternative was a new build or a structure-heavy reconductoring.
Decision Framework: When ACCC Makes Sense (and When It Doesn’t)
The most useful way to think about ACCC versus ACSR is not which is “better,” but which is appropriate for a given project’s constraints. The table below summarizes the scenarios where each conductor is typically the right engineering choice.
| Scenario | Typical right answer | Why |
|---|---|---|
| Reconductoring an existing corridor without rebuilding towers | ACCC or another HTLS conductor | Low high-temperature sag preserves clearance on existing structures. |
| Corridor that is already at thermal limits and cannot be widened | ACCC (or ACSS/ACSS-TW) | Higher operating temperature and lower resistance both raise the thermal ceiling. |
| High-loading corridor where I²R losses dominate operating cost | ACCC | Lower resistance reduces losses over the entire service life. |
| Greenfield transmission with no clearance constraints, moderate loading | ACSR | Lower CapEx and proven, well-stocked supply chain. |
| Distribution lines and short spans | ACSR (or AAC) | Mechanical and thermal demands well within ACSR’s range; ACCC premium not justified. |
| Projects in regions without trained ACCC installation crews | ACSR or domestically supported HTLS option | Installation execution risk outweighs the performance benefit. |
The pattern is clear: ACCC is at its strongest in reconductoring scenarios, on thermally-constrained corridors, and on heavily loaded lines where lifecycle loss savings are large. ACSR remains the right default for new construction on uncongested corridors, for distribution and short spans, and anywhere the project’s economics do not justify a premium conductor or where supply chain and skills constraints make ACCC impractical.
ACCC’s composite core is mechanically very different from a galvanized steel core and requires different field practices. The core is strong in tension but brittle in bending: minimum bending radii during stringing must be strictly observed, and any kink or crush damage during installation can compromise the core in ways that are not always detectable by visual inspection.
Dead-end and full-tension splice hardware for ACCC is not interchangeable with ACSR hardware — it must be matched to the specific core and aluminum design from the conductor manufacturer. Stringing operations should use bonded or running grounds appropriate for composite-core conductors, and crews should be trained in the specific procedures for the conductor type. Field repair options are more limited than for ACSR, so installation quality control is doubly important.
The ZD Cable Perspective: Our HTLS Product Line
ZD Cable does not manufacture composite-core conductors. ACCC, ACCR, and similar polymer- or ceramic-core designs sit outside our production scope. What we do manufacture, and what we recommend for engineers and procurement teams who are evaluating high-temperature, low-sag options as part of a reconductoring or capacity-upgrade project, is the following:
ACSS →
Aluminum Conductor Steel-Supported. Fully annealed 1350-O aluminum strands on a galvanized or aluminum-clad steel core. Continuous operating temperature 200–250°C. Our standard high-temperature offering.
ACSS/TW →
ACSS with trapezoidal-shaped aluminum strands for a denser cross-section in the same diameter envelope. Same 200–250°C thermal rating, with higher ampacity than round-strand ACSS at the same OD.
TACSR →
Thermal-Resistant Aluminum Conductor Steel-Reinforced. Zirconium-aluminum alloy strands over a conventional steel core. Continuous operating temperature approximately 150°C. A capacity-uprating option that retains standard-ACSR hardware compatibility.
For an engineering walk-through of when ACSS replaces ACSR, our companion article ACSR vs ACSS Conductor: Standard vs High-Temperature Operation covers the same decision framework applied to the steel-core HTLS path. For a broader view of the HTLS landscape including TACSR, ACSS, ACCC, and ACCR side by side, see ACSR vs HTLS Conductors: Is It Time to Upgrade?. Procurement teams ready to specify can request a technical quote on our ACSS product line.
Frequently Asked Questions
Is ACCC always better than ACSR?
No. ACCC outperforms ACSR on ampacity, high-temperature sag, and line losses, but it costs roughly 1.8× to 2.5× as much per kilometer at the factory gate, requires specialized hardware and trained installation crews, and only pays back economically when those advantages translate into avoided tower modifications, deferred substation upgrades, or significant loss savings on a heavily loaded line. For a greenfield project with modest loading and no clearance constraints, ACSR is usually still the more economical choice.
By how much can ACCC increase ampacity compared to ACSR?
For conductors of the same overall diameter, ACCC typically delivers a 25–50% increase in continuous ampacity over a comparable ACSR. The gain comes from two combined effects: ACCC has roughly 28–30% more aluminum cross-sectional area in the same OD, which lowers DC resistance by around 20–25%; and ACCC’s 180°C continuous temperature rating is roughly double ACSR’s 90°C limit, which gives the conductor much more thermal headroom before reaching its operating ceiling.
Does ACCC use more aluminum than ACSR?
Yes. At the same overall diameter, ACCC typically contains 28–30% more aluminum by cross-sectional area than ACSR. This is the direct geometric consequence of replacing a relatively bulky galvanized steel core with a slimmer composite core that occupies less of the conductor cross-section. The use of trapezoidal (TW) aluminum strands instead of round wires also helps, because trapezoidal strands pack more efficiently and leave less interstitial empty space.
How much does ACCC cost compared to ACSR per kilometer?
As a rough rule of thumb, ACCC conductor itself costs approximately 1.8× to 2.5× the per-kilometer price of an ACSR of equivalent diameter at factory gate, with specialized dead-end and splice hardware adding further cost. Exact pricing depends on the project’s specifications, aluminum and resin commodity prices, and supply geography. The cost gap narrows significantly when total project cost is considered — including any tower modifications avoided thanks to ACCC’s low high-temperature sag, and the value of reduced I²R losses over a 30–40 year service life.
Can ACCC be installed on existing ACSR transmission towers?
In most cases, yes — and this is the primary reason ACCC is used in reconductoring projects. ACCC’s very low coefficient of thermal expansion keeps sag at high operating temperatures dramatically lower than ACSR, which usually means the conductor can be strung on the existing tower structures without violating ground or phase-to-phase clearances. A clearance study and structural review are still required because higher mechanical tension and different conductor weights may affect tower loadings, but full tower replacement can often be avoided. This avoided structural work is what makes the ACCC business case work on many reconductoring projects.
Does ZD Cable manufacture ACCC conductors?
No. ZD Cable’s bare-conductor product line covers ACSR, AAC, AAAC, ACAR, ACSS, ACSS/TW, TACSR, and OPGW, along with ABC and service drop cables. Composite-core conductors including ACCC sit outside our manufacturing scope. For high-temperature, low-sag applications, our recommended path is ACSS or ACSS/TW — both deliver continuous operating temperatures of 200–250°C with proven steel-core mechanical performance. Engineering teams evaluating ACCC for a reconductoring project are welcome to contact us for a comparative assessment with our HTLS conductor lineup.
