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.
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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.

Magnetism

The generation of electric power depends on magnetism or the principles of magnets. Most of us have seen a magnets' ability to attract certain metals, such as iron. Any material that can attract metals is called a "magnet". The attractive ability of these materials is called "magnetic force". Certain specimens of iron ore possess this attracting property when they are taken from the earth. One name for this material is magnetite or lodestones.

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Magnets
Electromagnetic Fields
Electromagnets
Magnetic Induction Principles

Magnets

The basic atomic structure of a magnet seems to align most of the molecules in the same direction. It's possible to see this force through a simple experiment:

Put a bar magnet under a sheet of glass and sprinkle iron filings on the glass. The lines of force from the magnet show up clearly as the filings form a pattern. Notice that the attractive forces are greatest at the two ends of the magnet, where the majority of filings gather. We call these ends "poles".

The density of the pattern represents the strength of the field, which is the magnitude of the force exerted upon a magnetic material placed at the point in the field. These lines are called lines of magnetic flux.

If we suspend a magnet by a string from its center so that it is free to turn, it will turn until there axis lines up with its poles, lying along the earth's magnetic north and south poles. The pole which points north is called the north pole and the other is called the south pole. These are usually designated by an N and S marked on the magnets.

Let's add another magnet to our experiment and we will notice another key property of magnets.

The like poles will repel one another, while the unlike poles will attract one another. This is a very important principle since the generation of electric power depends on these laws of attraction.

Almost all commercially available magnets are artificial. They were manufactured to be magnets by using other magnets to create the correct molecular alignment.

There are two types of magnets: temporary and permanent. Temporary magnets are those which will hold their magnetism only as long as the magnetizing force is maintained. These are usually found inside motors.

Permanent magnets are those which will hold their magnetism after the magnetizing force has been removed and will continue to be magnets for as long as they are not disturbed by being jarred or heated.

Electromagnetic Fields

The flow of electricity through a conductor produces both an electric and magnetic field around the conductor. Collectively, these two fields are referred to as an electromagnetic field or EMF. The strength of the electric field is measured in volts per meter and varies with the amount of the source voltage. The higher the source voltage, the higher the strength of the field. Electric field strength decreases rapidly with distance from the source.

Electric fields are produced both naturally and by any conductor carrying electricity. The strength of the earth's natural electric field varies, but on average is about one-thousandth of a volt per meter. Electric field strength typically varies from 10 to 150 volts per meter under electric distribution lines and 5 to 100 volts per meter inside homes and workplaces.

The strength of a magnetic field is typically measured in units of gauss or milligauss and varies with the amount of current moving through a conductor. Lines or devices requiring high levels of current flow produce stronger magnetic fields than those with low current flow. For example, the measure of a magnetic field directly under a high voltage transmission line is somewhere between 20 to 650 milligauss. The magnetic field measured underneath a lower power distribution line is .5 to 30 milligauss.

Magnetic fields produced by electrical circuits drop off rapidly with distance from the source. The magnetic field produced by a microwave at 1 foot is 70 to 100 milligauss while at five feet away, the magnetic field strength drops to five milligauss.

Electric fields are blocked by shielding such as walls, houses, trees, other vegetation, soil, and other large dense objects. Magnetic fields, on the other hand, pass easily through most objects and are only blocked by structures containing large amounts of iron or iron alloy metals.

Electromagnets

Electromagnets play an essential role in the operation of generators, motors, transformers, and relays. Electromagnets are constructed by wrapping an insulated conductor wire around an iron object, like a large nail, and then passing an electrical current through the wire. The strength of the electromagnet depends on the number of wraps, the size of the wire, and the amount of current flowing through the wire.

Magnetic Induction Principles

Michael Faraday discovered in 1831 that if a coil of copper wire is rotated in a magnetic field in such a way as to cut across the lines of magnetic force, an electric charge is created or induced in the wires. This is the basic principle by which practically all our present day electric current is generated.

Generators use magnetic induction to produce electrical energy. Electrical current is generated by moving wires through a magnetic field. The wire loop inside the generator is mechanically driven by some source of rotary motion. The source of power for the rotation might be fossil fuels, falling water or nuclear energy. As the wire loop spins inside the magnetic field, an electric current is produced in the wire. This current becomes the basis for commercially available electrical energy.

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Electrical standards

There are several major organizations and codes that help to standardize equipment specifications and safety regulations within the electrical industry.

The first is NEMA, or the National Electric Manufacturers' Association. NEMA is a major force in standardizing electrical apparatus, making it easier for utilities to use different manufacturers' products interchangeably. NEMA issues technical standards and specifications, which are often cited in the manufacturers' descriptive data about its products.

Another important group is ANSI, the American National Standards Institute. ANSI also gets involved in setting equipment and operating standards for utilities.

And, finally, there is the National Electrical Code. This is a comprehensive building code standards book sponsored by the National Fire Protection Association. it's revised every three years and its primary purpose is the protection of life and property. in fact, the original NEC was written in 1897 and was the combined effort of the insurance, electrical and architectural industries. In addition to NEC, the National Fire Protection association issues other standards related to the electrical field, which you'll also want to consult if your region has adopted them as law