Technical article
Difference between ACSR and ACSS conductors in high-voltage fittings
What sets an ACSR conductor apart from an ACSS one, why it matters when choosing connectors and fittings, and how Partalum handles it in transmission lines.
ACSR (Aluminum Conductor Steel Reinforced) and ACSS (Aluminum Conductor Steel Supported) conductors are two types of bare cable for overhead transmission and substation lines. In both, aluminum wires surround a steel core; the key difference is how the mechanical load is shared and the operating temperature. In ACSR, aluminum and steel share the mechanical tension and the aluminum is hardened (tempered). In ACSS, the aluminum is fully annealed (soft) and it is the steel core that carries practically the entire mechanical load, which allows the conductor to operate at higher temperatures with less loss of strength and higher current-carrying capacity (ampacity). Partalum manufactures compression connectors and fittings for both conductor types, in accordance with CFE specifications.
This distinction is not academic: it determines which clamp, which splice and which assembly is specified. A part designed only for ACSR may not be the right one for a line reconductored with high-temperature ACSS.
What does each acronym mean?
- ACSR — Aluminum Conductor Steel Reinforced. 1350 aluminum wires over a galvanized steel core. The steel reinforces: it provides mechanical strength while the aluminum conducts. It is the most widespread transmission conductor.
- ACSS — Aluminum Conductor Steel Supported. Same aluminum-over-steel geometry, but the aluminum is annealed and the steel supports almost the entire load. It allows continuous high-temperature operation (typically up to ~200–250 °C, depending on the core grade; exact temperature to be confirmed against the project specification) with less thermal sag than equivalent ACSR.
Why does it matter for the fitting and the connector?
| Criterion | ACSR | ACSS |
|---|---|---|
| Aluminum | Hardened (tempered) | Annealed (soft) |
| Carries mechanical load | Aluminum + steel | Steel core |
| Operating temperature | Standard | High temperature |
| Typical application | New lines, general use | Reconductoring, more ampacity |
| Partalum fitting | Compression clamps and splices | High-temperature ACSS line |
Because in ACSS the annealed aluminum is softer, suspension clamps and compression splices must transfer the load to the steel core without over-compressing or damaging the aluminum layers. That is why Partalum offers a dedicated line for high-temperature ACSS conductor within the substation connector family, in addition to the clamps and splices for ACSR. The voltage level covered ranges from distribution up to 400 KV, and the mechanical strength of the string and tension fittings is declared in the 80–480 KN range.
How to choose between one and the other?
The conductor selection is defined by the project (CFE, the engineering team or the contractor) based on the required ampacity, the allowable sag and whether it is a new line or a reconductoring job. Once the conductor is fixed, the fitting is specified accordingly: conductor type (ACSR, ACSS, AS or MCM copper), voltage level in KV, function (suspension, tension, splice, dead-end) and applicable standard (CFE, NMX-ANCE).
Partalum works against specification: if your line is ACSR or ACSS, tell us the conductor size, the voltage level and the project standard and we will confirm the correct clamp, splice or assembly.
Related reading
- Substation connectors — includes the high-temperature ACSS line.
- Transmission line assemblies — suspension and tension for 1–4 conductors per phase.
- What suspension and tension assemblies are
FAQ
What engineering asks about this topic.
What is the main difference between an ACSR and an ACSS conductor?
In ACSR (Aluminum Conductor Steel Reinforced) the aluminum is hardened and shares the mechanical load with the steel core. In ACSS (Aluminum Conductor Steel Supported) the aluminum is fully annealed and the steel core carries practically the entire mechanical load, which allows operation at higher temperature with more ampacity and less thermal sag.
Are the same connectors and fittings used for ACSR and ACSS?
Partalum manufactures compression connectors and fittings for both conductor types, in accordance with CFE specifications. The part is specified against the conductor and the project standard: a clamp or splice designed only for ACSR may not be the right one for a line reconductored with high-temperature ACSS.
At what temperature does an ACSS conductor operate?
ACSS allows continuous high-temperature operation, typically up to around 200–250 °C depending on the grade of the steel core. The exact temperature is confirmed against the project specification (to be confirmed).
What advantage does ACSS offer when reconductoring a transmission line?
Compared with an equivalent ACSR, ACSS supports a higher continuous operating temperature and higher current-carrying capacity (ampacity) with less thermal sag, which is why it is used when reconductoring lines. The final selection is defined by the project engineering against its specification.