Underground Structures

Underground structures describe the features and objects needed to support an underground electric system, including underground residential distribution (URD).

The central component of URD and other underground systems is the single-phase distribution transformer, which is usually housed in heavy, corrosion-resistant tanks for installing in subsurface vaults, known as submersible.

Most URDs include the following components: pad-mounted, dead-front transformer; primary laterals operated as open loops; 12.47 grounded Y/7.2 kV primary voltage; two primary cable connections per transformer; front-lot construction; four to eight homes per transformer; internal fusing; and direct-buried cables.

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