Power cable

The first power distribution system developed by Thomas Edison in 1882 in New York City used copper rods, wrapped in jute and placed in rigid pipes filled with a bituminous compound.

[3] Typical residential and office construction in North America has gone through several technologies: Modern power cables come in a variety of sizes, materials, and types, each particularly adapted to its uses.

The armor may be made of steel or aluminum, and although connected to earth ground is not intended to carry current during normal operation.

Special purpose power cables for overhead applications are often bound to a high strength alloy, ACSR, or alumoweld messenger.

PAC can be ordered unjacketed, however, this is less common in recent years due to the low added cost of supplying a polymeric jacket.

For shorter vertical transitions (perhaps 30–150 feet) an unarmored cable can be used in conjunction with basket (Kellum) grips or even specially designed duct plugs.

Material specification for the cable's jacket will often consider resistance to water, oil, sunlight, underground conditions, chemical vapors, impact, fire, or high temperatures.

When cables must run where exposed to mechanical damage (industrial sites), they may be protected with flexible steel tape or wire armor, which may also be covered by a water-resistant jacket.

This metallic shield can consist of a thin copper tape, concentric drain wires, flat straps, lead sheath, or other designs.

Cables of 10 kV or higher may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminum or lead sheath.

For higher voltages the oil may be kept under pressure to prevent formation of voids that would allow partial discharges within the cable insulation.

Unfortunately, oil leaks into soil and bodies of water are of grave concern and maintaining a fleet of the needed pumping stations is a drain on the O+M budget of most power utilities.

All electrical cables are somewhat flexible, allowing them to be shipped to installation sites wound on reels, drums or hand coils.

Flexibility is an important factor in determining the appropriate stranding class of the cable as it directly affects the minimum bending radius.

At times, a solid conductor medium voltage cable can be used when flexibility is not a concern but low cost and water blocking are prioritized.

Heavy duty flexible power cords such as those feeding a mine face cutting machine are carefully engineered — their life is measured in weeks.