All About Electrical Conductors Most Frequent Questions
What is Conductor ac Resistance
A conductor offers a greater resistance to a flow of alternating current than it does to direct current. This increased resistance is generally expressed as the ac/dc resistance ratio. The two major factors for this increase are the skin effect and the proximity effect of closely spaced current carrying conductors. Other magnetic effects can also cause an additional increase in ac/dc resistance ratios.
What is Electric Fields and Voltage
Current flow is charge in motion. We might consider the simple case of a conductor carrying current out to a load and then a return conductor as two separated parallel cylinders of charge. If we neglect conductor diameter line of charge there are electric field lines represented by circles of diameters such that the center of the circles are on the 0 line and each circle passes through the center of the cylinders.
What is Conductor
Conductors may be solid or stranded. Metals used are commonly copper or aluminum. An attempt to use sodium was short-lived. The strand can be concentric, compressed,compacted, segmental, or annular to achieve desired properties of flexibility, diameter, and current density.
What is Circular Mil Sizes
Sizes larger than #4/0 AWG are specified in terms of the total cross-sectional area of the conductor and are expressed in circular mils. This method uses an arbitrary area of a conductor that is achieved by squaring the diameter of a solid conductor. This drops the π/4 multiplier required for the actual area of a round conductor. A circular mil is a unit of area equal to the area of a circle having a diameter of one mil, one mil equals 0.001
inch. Such a circle has an area of 0.7854 or π/4 square mils. Thus, a wire 10 mils in diameter has a cross-sectional area of 100 circular mils. Likewise, one square inch equals 4/π times 1,000,000=1,273,000 circular mils. For convenience, this is usually expressed in thousands of circular mils and abbreviated kcmil.
What is Non-Shielded Power Cable
A cable non-shielded cable may consist of one or several conductors and one or several
insulating layers. The cable may contain a jacket. The cable may also include a conductor
shield. A cable is not considered fully shielded until both conductor and insulation shields
are present. Non-shielded cables are common in the 0 to 5 kV voltage range although
non-shielded power cables through 8 kV have been available.
What is AIR INSULATED CONDUCTORS
A metallic conductor suspended from insulating supports, surrounded by air, and carrying electric signals or power may be considered as the simplest case of an insulated conductor.
What is INSULATING TO SAVE SPACE
Space is a common constraint that precludes the use of air as an insulator. Imagine the space requirements to wire a house or apartment using bare conductors on supports with air as the insulation. A voltage divider has been created that is made up of the impedance from the conductor to the outside covering surface and another impedance from the covering surface to ground. The distribution of voltage from conductor to the surface of the covering and from the covering surface to ground will be in proportion to these impedances.
What is RISING VOLTAGE
Return to the metallic conductor that is covered with an insulating material and suspended in air. When the ground plane is brought close or touches the covering,At low voltages, the effect is negligible. As the voltage increases, the point is reached where the potential gradients are sufficient to cause current to flow across the surface of the covering.
What is Electrical Insulation or Dielectric
The insulation dielectric provides sufficient separation between the conductor and the nearest electrical ground to adjacent phase to preclude dielectric failure. For low voltage cables, (2,000 volts and below), the required thickness of insulation to physically protect the conductor is more than adequate for required dielectric strength.
What is Jackets in a Condcutors
In low voltage applications, jackets are commonly used to protect underlying layers from physical abuse, sunlight, flame, or chemical attack. In medium voltage shielded cables chemical attack includes corrosion of underlying metallic layers for shielding and armoring. In multi-conductor designs, overall jackets are common for the same purposes. For medium and high voltage cables, jackets have been almost universally used
throughout the history of cable designs.
What is Medium Voltage Shielded Cables
Medium voltage cables generally are fully shielded having both conductor and insulation shield cables in the 5 kV through 35 kV voltage range.
What is Electric Field
Emphasis will be on 60Hz alternating current fields. In all cables, regardless of their kV ratings, there exists an electric field whenever the conductor is energized. This electric field can be visualized as electric field lines and lines of equipotential.
What is Equipotential Lines
Equipotential lines represent points of equal potential difference between electrodes having different electrical potentials.
What is Metric Designations
All of the world, except for North America, uses the SI unit of square millimeters (mm2) to designate conductor size. The International Electrotechnical Commission has adopted IEC 280 to define these sizes. An important consideration is that these are not precise sizes. For instance, their 50 mm2 conductor is actually 47 mm2. To accommodate everyone, the IEC standard allows as much as a 20% variation in conductor area from the size designated.
What is Skin Effect
In ac circuits, the current density is greater near the outer surface of the conductor. The current tends to crowd toward the outer surface. This is called skin effect. A longitudinal element of the conductor near the center of the axis is surrounded by more lines of magnetic force than near the rim. This results in an increase in inductance toward the center.
