OVERHEAD TO UNDERGROUND CONNECTION TUTORIALS AND BASIC INFORMATION

With the advent of plastic-insulated cables, connections have been made directly between the overhead and underground conductors. Live-line clamps furnish a means for easy and rapid disconnection of the conductors involved.

Potheads and weatherheads are dispensed with. In older installations, many of which will continue to exist, special devices have been used. For primary voltages, potheads have been used. Here the conductors of the underground cable are connected to terminals in which the conductors are surrounded by poured insulation compound to prevent moisture or air from entering the cable insulation.

The overhead wires are connected to the female end of the terminal, enclosed in an insulated cap. The connection is made by placing the cap over the terminal extending from the pothead case.

Potheads so described are known as disconnecting potheads. Where the connections are made directly to the terminal extending from the pothead in a permanent fashion, the pothead does not carry this distinction.

For lower secondary voltages of 500 V or less, a simpler device was used. Here the conductors of the underground cable are brought out through a preformed insulator, usually of porcelain, in an assembly which inverts the leads so that rain cannot enter the cable. Such devices are known as weatherheads.

Ties are pieces of wire used to attach the conductors to the insulators on overhead systems. They should be flexible enough to be handled easily, but must be mechanically strong to prevent the conductor from pulling away from the insulator under stress.

For bare copper conductors, this tie wire is usually of soft-drawn copper; for weatherproof covered conductors, bare or weatherproof covered wire is used. For aluminum or ACSR conductors, soft-drawn aluminum wire is used.

Wire sizes are optional, but are generally small enough to be flexible but strong enough for the purpose. Often such ties are made from old or discarded conductors of small sizes, no. 6 or no. 8 conductor.

Where such ties are handled while the conductors remain energized, ties designed with loops that can be handled with so called hot-line tools or hot sticks are employed.

For special conditions, especially for live-line operations, clamps that are designed to hold the conductors, but are easily opened, are used. The economics of such clamps, however, are such that they are rarely used. Tie wires are almost universally used.

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