circuit spacing

Maximize HDD Accuracy When Undergrounding High-Voltage Transmission Lines

Rapidly changing physical and political environments have many utility owners re-evaluating the feasibility of undergrounding significant portions of their electrical networks. Once considered prohibitively expensive, liabilities stemming from wildfires and other natural disasters, as well as new research on total lifecycle costs, has many network owners publicly committing to significant capital expenditures for new underground electrical installations. Horizontal directional drilling will play a key role in this transition.

While the absolute location of underground electrical infrastructure is important, the relative distance between bores is critical. Multiple parallel circuits in close proximity within a limited right of way pose unique challenges for underground transmission lines. If high-voltage transmission circuits are installed too closely, excess heat buildup can decrease transmission efficiency or even cause insulation failure.

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Measures to prevent overheating include the use of XLPE and/or pressurized cables, the use of spacers to maintain consistent separation of the conduits, as well as specialized thermal grouts that maximize heat transfer into the surrounding earth. When multiple circuits are installed underground in parallel, the engineered design is limited by how closely they may be placed.

Precisely positioning each pilot bore in parallel to the actual installed location of other installed circuits is critical to any underground transmission plan. ParaTrack2 (P2) Underground is the only HDD guidance system designed for parallel underground installations. By running an electrified guide wire in an adjacent line to be paralleled, P2 Underground acts as an ‘end to end’ guidance system that allows the drilling of parallel ‘twins.’ This twinning ensures circuits are parallel to the actual installed product along the entire length.

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P2 Underground is available as part of the ParaTrack HDD Guidance System, available exclusively from your local Prime Horizontal or Inrock dealer. To learn more about ParaTrack’s role in undergrounding utilities of all types, visit us at