Power Cables

Modern power cables come in a variety of sizes, materials, and types, each particularly adapted to its uses. Large single insulated conductors are also sometimes called power cables in the industry.

Power cables consist of three major components: conductors, insulation, and a protective jacket. The makeup of individual cables varies according to application. The construction and material are determined by three main factors:

Working voltage, determining the thickness of the insulation;
Current-carrying capacity, determining the cross-sectional size of the conductor(s);
Environmental conditions such as temperature, water, chemical or sunlight exposure, and mechanical impact, determining the form and composition of the outer power cable jacket.

Power cables for direct burial or for exposed installations may also include metal armor in the form of wires spiraled around the power cables, or a corrugated tape wrapped around it. The armor may be made of steel or aluminum, and although connected to earth ground is not intended to carry current during normal operation.

Power cables use stranded copper or aluminum conductors, although small power cables may use solid.

The cable may include insulated conductors used for the circuit neutral or for ground (earth) connection.

The overall assembly may be round or flat. Non-conducting filler strands may be added to the assembly to maintain its shape. Special purpose power cables for overhead or vertical use may have additional elements such as steel or Kevlar structural supports.

Some power cables for outdoor overhead use may have no overall sheath. Other cables may have a plastic or metal sheath enclosing all the conductors. The materials for the sheath will be selected for resistance to water, oil, sunlight, underground conditions, chemical vapors, impact, or high temperatures. Cable materials may be specified not to produce large amounts of smoke if burned. Cables intended for underground use or direct burial in earth will have heavy plastic or metal, most often lead sheaths, or may require special direct-buried construction. When cables must run where exposed to mechanical impact damage, they may be protected with flexible steel tape or wire armor, which may also be covered by a water resistant jacket.

For circuits operating at or above 2,000 volts between conductors, a conductive shield may surround each insulated conductor. This equalizes electrical stress on the cable insulation.

Cables for power distribution of 10kV 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.

Modern high-voltage cables use polymers or polyethylene, including XLPE for insulation. They require special techniques for jointing and terminating.

Many multi-conductor cables have a bare or insulated grounding or bonding wire which is for connection to earth ground. The grounding conductor connects equipment enclosures to ground for protection from electric shock.

Electrical power cables are often installed in raceways, including electrical conduit and cable trays, which may contain one or more conductors.

A hybrid cable can include conductors for control signals or may also include optical fibers for data.

All electrical cables are somewhat flexible, allowing them to be shipped to installation sites wound on reels or drums. Where applications require a cable to be moved repeatedly, such as for portable equipment, more flexible cables called “cords” or “flex” are used. Flexible cords contain fine stranded conductors, not solid core conductors, and have insulation and sheaths to withstand the forces of repeated flexing and abrasion. Heavy duty flexible power cords such as those feeding a mine face cutting machine are carefully engineered — their life is measured in weeks. Very flexible power cables are used in automated machinery, robotics, and machine tools. Other types of flexible cable include twisted pair, extensible, coaxial, shielded, and communication cable.

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