Wire Characteristics

Wire Characteristics
Electrical wires must be able to carry current safely without overheating and being damaged. Characteristics of wires include the following:
The current carrying capacity of a particular wire is dictated by its "ampacity" - how many amps it can handle. Ampacity is a function of the cross section area or diameter of the wire and its material type. Larger diameter wires have larger cross section areas and can safely carry more electrical current without overheating. The maximum ampacity for different types of wires is reported in the electrical codes used throughout the industry. These tables are based on the size of the wire and the particular insulation type for the particular wire.

Insulation Type is important since some insulation materials dissipate heat better than others
Insulation Type
The insulation around a wire has two purposes:
• to prevent contact with other conductors, the ground and other conductive objects; and
• to shield the wire from physical damage.
The type of insulation determines the environment in which it can be used safely. Wires used indoors are subjected to less exposure to the elements than those designed for outdoor use. Outdoor wiring is exposed to water and ultraviolet light, so the insulation is designed to withstand these elements. Insulation on wires buried in the ground must also be able to withstand the damp, corrosive environment of the soil.
Most of today's electrical wires have insulation coverings made of plastic or thermoplastic which provides a long, durable life. Many older wires used cloth insulation. Rubber was also common, but is not used as much any more since it becomes brittle and deteriorates over time.
The National Electrical Code gives various letter designations and classifications for different types of insulation on electrical wires. These letter designations help indicate the type of material the insulation is made of and in what type of environment it can safely be used without deteriorating.
Wire Size
Electrical wire sizes are indicated using two different systems: the American Wire Gauge System (AWG) and the Thousand Circular Mill system (KCMIL), which was known until recently as (MCM). Both systems designate wire size based on their diameter or cross sectional area. The American Wire Gauge system is used to refer to relatively small wires.
More Information


AWG
In the American Wire Gauge or "AWG" system, as the wire gets smaller, the number of the wire gets larger. The smallest AWG size is 40 and looks like a metal thread.

Common electrical extension cords on lamps are typically 18 gauge wire. The smallest gauge allowed for lighting and receptacle circuits in a house is 14 gauge wire. The gauge sizes get smaller with corresponding increases in the wires diameter all the way down to 0 gauge.
At that point, the industry labeled the next larger size as double zero, commonly referred to as 2 ought. The next AWG size larger than 2 ought is triple zero or 3 ought. Four ought is the largest AWG wire size designation. Wires larger than this size are designated by the Thousand Circular Mill system or "KCMIL" sizes.
KCMIL
All wire sizes larger than 4 ought AWG are given as KCMIL sizes. KCMIL wire size is the equivalent cross sectional area in thousands of circular mills. A circular mill is the area of a circle with a diameter of one thousandth (0.001) of an inch. Notice that the wire sizes in the KCMIL system increase as the numbers get larger, which is exactly opposite from the AWG system.

Solid Vs Stranded
Electrical wires are either solid or stranded conductors. Solid conductors are exactly that, one solid wire. Stranded conductors consist of a wire made of a number of smaller wire strands wrapped around each other.
The choice between solid or stranded depends on the need for flexibility in handling and working with the wire. Smaller electrical wire sizes are generally made of solid conductors while wires larger than Number 6 AWG are generally stranded. The cross section area or circular mill size of a stranded conductor is equivalent to that of a solid conductor for the same designated wire size. This means when looking at a Number 10 stranded wire or solid wire, the Number 10 stranded will look slightly larger in diameter but has the exact same cross section area of conductive material as the solid wire.
Extension cords are made of stranded wires since they require flexibility allowing the cord to be bent and twisted without stressing the electrical wires.