SMALL CONDUCTORS SAVE SPACE
Compact conductors squeeze more metal into smaller space.
- Published in Southwire's Power Cable Update newsletter in May/June 1998
- Reprint permission granted
Not all conductors are created equal. You can have two 500kcmil stranded conductors, for instance, with different diameters. One will have a diameter of 0.813" while the other measures 0.736" What makes the difference? Compression of the strands.
Squeeze the strands to save space
"Compact stranding, are conductor constructions that can let you put a little more ampacity into a tight space," says Dave Mercier, applications engineering manager.
In conventional conductors, layers of wire that wrap to the right alternate with layers that wrap to the left. This is called reverse-lay concentric stranding. Because there are air spaces among the strands, the diameter of the stranded conductor is larger than a solid conductor with the same cross-section of copper.
In compressed-strand construction, the stranded conductor passes through a die that squeezes and flattens the outer layer of strands. The total cross-sectional area of the copper stays constant, but now the outer strands fit closely together and the conductor has a 3 percent smaller diameter.
Compact-strand construction carries the process one step further. In compact-strand conductors, the inner strands have been squeezed together also. The conductor diameter is even smaller, typically about a 6 percent further reduction, while the cross-sectional area of the copper is still the same.
ASTM sets size standards
The degree of compression in compressed and compact stranding is defined by ASTM standards. In our 500kcmil example, the difference in conductor diameter amounts to about nine percent. You trade off some flexibility to get the smaller conductor. Compact stranding is a little more difficult to bend than conventional stranding.
"In some applications, the size reduction in compressed and compact stranding can be significant," Mercier says. "If you're upgrading cables in existing ducts, for example, compact stranding may give you more ampacity." |
