The covering on a covered conductor gets most of the attention, but the stranded conductor underneath decides how far the line can span, how much it sags and how it behaves in a salt-laden or polluted atmosphere. APAR covered conductors from 11 kV to 132 kV are offered with four conductor types, in sizes from 100 to 400 mm². The table below sets them side by side. Details of the covering itself are in the covered conductor construction chart.
The four core types
| Core | What it is | What it favours | What to watch |
|---|---|---|---|
| AAAC | Stranded all-aluminium alloy, no steel | Corrosion resistance, light weight, coastal and polluted routes | Tensile strength comes from the alloy alone, so very long spans need checking |
| ACSR | Aluminium strands over a galvanised steel core | High strength for longer spans and heavier loading | The steel core carries much of the tension and needs its zinc coating protected from damp |
| ACSS | Fully annealed aluminium strands over a steel core, with the steel carrying essentially all the tension | Low sag and low creep at elevated temperature | A bare ACSS may be allowed far higher temperatures than any covering permits, so the covering sets the thermal limit |
| AL59 ACS | High-temperature option in the APAR range | Higher operating temperature than the other three | Confirm size and voltage class availability with APAR |
Temperature is set by the covering
The APAR product page lists an operating temperature of up to 95°C for the covered conductor, and up to 105°C for the AL59 ACS version. These figures apply to the finished covered conductor, not to the bare metal. A bare conductor of the same type may be rated hotter, but the XLPE covering is what limits the covered line. Ampacity from a bare-line table should therefore never be carried over unchanged.
Four questions that decide the core
- What is the longest span, and what tension does it imply? Long spans or heavy wind and loading point towards a steel-cored type. Short urban spans may not need one.
- How aggressive is the atmosphere? Coastal and industrial routes put salt and chemical deposits on every surface. An all-aluminium alloy core has no steel to corrode if the covering is ever breached.
- How hot will the conductor run at peak load? Compare the expected conductor temperature with the 95°C and 105°C limits above, with margin for hot ambient conditions.
- What does the existing line carry? A covered conductor adds weight compared with a bare conductor of the same size, so pole strength and sag must be checked against the covered conductor’s own table.
Next steps
Match the shortlisted core to a voltage class using the covered conductor selection guide, then write it into the specification using the tender specification checklist. For the product range and accessories, see the APAR covered conductor page. To compare covered conductor with bare overhead types, read Overhead Line Conductors Compared. Technical particulars and test certificates are available from APAR on request.