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 CHAPTER 2. POWER DISTRIBUTION CABLE SYSTEMS.
2.1 CABLE SPECIFICATIONS. A cable is defined as a single conductor or an assembly of
conductors covered by solid electrical insulation. Cable specifications generally start with the
conductor and progress radially through the insulation and coverings. The following is a typical
list of specifications:
(a) Number of conductors in cable.
(b) Conductor size (American Wire Gage (AWG), circular mil) and material.
(c) Insulation type.
(d) Voltage rating.
(e) Shielding system.
(f) Outer finishes (or sheath).
(g) Installation.
An alternate method of specifying cable is to furnish the ampacity of the circuit (amperes (A)),
the voltage (phase to phase, phase to ground, grounded, or ungrounded), and the frequency, along
with any other pertinent system data.
2.2 CABLE CONSTRUCTION. A typical cable is comprised of conductors shielded by various
types of material. The cable may have one conductor or three conductors grouped as one.
2.2.1 Conductors. The two conductor materials in common use are copper and aluminum.
Copper has historically been used for conductors of insulated cables primarily for its desirable
electrical and mechanical properties. The use of aluminum is based mainly on its favorable
conductivity-to-weight ratio (the highest of the electrical conductor materials), its ready
availability, and the stable low cost of the primary metal.
2.2.1.1 Comparison Between Copper and Aluminum. Aluminum requires larger
conductor sizes to carry the same current as copper. The equivalent aluminum cable, when
compared to copper in terms of ampacity, will be lighter in weight and larger in diameter. For
distribution, aluminum is commonly rated as equivalent to a copper conductor two AWG sizes
smaller, which has almost identical resistance.
2-1
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