/images/TDUpdate2.gif/images/southwire_100x70.jpgWhen Trees Squeeze, These Wires Please - 2004WhenTreesSqueezeTheseWirePleaseJuly2004.htmTree-lined streets are a lovely urban picture – unless you have to run overhead distribution lines along them.
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When Trees Squeeze, These Wires Please - 2004

Tree wire and spacer cable simplify overhead distribution in tree-lined streets and tight rights of way.

Tree-lined streets are a lovely urban picture – unless you have to run overhead distribution lines along them.

“Tree limbs touching bare conductors invite tripped circuit breakers and service interruptions,” says Steve Campbell, chief engineer for Southwire’s Energy Division. “But cutting back the branches to clear the wires is a costly, recurrent maintenance operation. Severe trimming can also generate complaints from residents. Tree wire – and its first cousin, spacer cable – can be an answer. Both tree wire and spacer cable let utilities use tighter clearances and reduce tree-trimming budgets.”

Single-conductor or three-conductor choices

Tree wire is a single conductor protected by layers of polyethylene. The covering prevents direct shorts when a tree limb brushes the wire, and it resists tracking at distribution voltages up to 35kV. Tree wire is normally self-supporting.

Spacer cables are groups of three of those same covered conductors separated by tough, high-density polyethylene spacers. One run of three-conductor spacer cable can carry a three-phase distribution circuit in less right-of-way space than three individual conductors. Spacer cable is supported by a steel messenger wire running through the spacers.

“Three individual conductors on the cross arm of a pole give a single circuit,” says Campbell. “Utilities can hang a spacer cable bundle on each end of the same cross arm and double the circuits going into an area.”

Options in conductor design and size

Tree wire and spacer cable conductors can be aluminum conductor steel-reinforced (ACSR), all-aluminum alloy conductors, (AAAC) or all-aluminum conductors (AAC) with concentric, compressed, or compact stranding. Self-supporting tree wire normally uses ACSR. Messenger-supported spacer cable usually carries AAC wires. Both tree wire and spacer cable can be manufactured with conductors from AWG 4 to 795kcmil. “These are non-shielded covered conductors,” says Campbell. “They should be handled like bare conductors during installation and operation. Tree wire is normally accompanied by a bare ACSR ground wire. With spacer cable, the messenger is the ground wire.”

Campbell concludes, “Tree wire and spacer cable can be cost-effective solutions to common application problems. And you can get them easily as a part of Southwire’s family of power transmission and distribution products.”