Wires

Above: Superconducting wire can be made into a metallic "tape"

Above: Compact fluorescent light electronics, the transformer is very small and is designed very cheaply. These parts often fail before the end of the typical life cycle of the unit.`

Engineers and Costs Savings Design:

Engineers use mathematics to calculate the 'skin depth' to find out how much of the wire is being used to conduct electricity. This is a critical part of the electrical engineers work in design of power systems. This work is also related to cost savings as engineers can find out what gauge wire and what wire type to use and compare that with other materials and configurations. Older electric motors and generators from the beginning of the 20th century were known to last a long time because at that time engineers could design the windings and type of wire for best performance since the costs of appliances and machines were higher. Today many motors burn out because engineers are forced to use the cheapest option - the least amount of material which can handle the current, however when the motor begins to overheat thinner wires of cheaper material will burn out faster. Ballasts (transformers) in modern lighting systems have a notoriously short lifespan in the effort to keep the cost per unit down.

Hands-on Exercise: How Cost Effects Design

You can see and feel the work of engineers in wire design around your house. Simply find older power supplies or professional power supplies used with high cost machines or tools. Feel the weight of these wall-worts or power supplies. Now find a kids toy or mobile phone charger. Feel how light the transformers feel in comparison.
If you are lucky you can find two transformers which convert power from the wall (120 or 220 V) to the same DC voltage for a device. If you open up the casing you can see the difference in the size of the gauge of windings, and whether they use copper or aluminum. You will clearly see how cost of the overall item effects design.

Below: Types of wire used by utilities in power transmission:

Below: fixed wiring used in houses along with cords used in speakers, appliances and telephone systems. The graphic below shows old wires once used in houses (SJTWA and Type SE cable) and the modern standard romex.

WIRING 1880s to Today:

Above: 3 conductor underground copper wire (now rare)

Below: Flat 'tape' wire used in superconducting magnets

The best wire for the job:

All electrical engineers must know about wires and think about using the right design and material for the task at hand. Here are the factors for determining wire design:

-Durability (ability to flex repeatedly or be subject to crushing weights)
-Voltage and Current level
-Suspension strength (ability to hold its own weight over long spans between support)
-Underground or underwater
-Temperature of operation (like superconducting wire)
-Cost

Solid Wire:



Advantages:
Less surface area to corrode
Can be rigid and strong
Disadvantages:
Not good if flexed repeatedly, can break if flexed in the same spot
Not practical for high voltage

Stranded Wire:

Above: Stranded speaker wire found in every household
Below: Specialized use super-thick stranded copper wire

-Stranded wire - lots of smaller wires in parallel, can be twisted together
Advantages:
Great conductor for its size
Disadvantages:
You may think this would be good for high frequency use because it has lots of surface area on all the little strands of wire, however it is worse than solid wire because the strands touch each other, shorting, and therefore the wire acts as one larger wire, and it has lots of air spaces which makes for more resistance for the size

Braided Wire:


Advantages:
-Great for durability compared with solid wire
-Better conductivity than solid wire (lots of surface area)
-Can act as an electromagnetic shield in noise-reduction wires
-The more strands in the wire, the more bendable and strong it is, but it costs more

Special Wires:



Solid with braided exterior or some combination of this, these wires are used for all kinds of special applications.

Coax cable is used for radio or cable television transmission because in its design braided and foil conductors on the outside keep frequencies trapped inside.  The shielding prevents stray electromagnetic energy from tainting the area around sensitive receivers.

Hands-on Exercise: Wire Guessing Game

Gather bits of scrap wire from around you house or school workshop, collect short samples of different types. Now use the charts above to figure out what kind of wire it is, what it is made of, and list the uses for each. Show this to your teacher and see if you guessed right. Wire comes in so many exotic types that you may find yourself with a real mystery on your hands. Use internet searches to try to identify all of your samples.

4.) WIRE INSULATION:

Left: To make an efficient motor or generator windings have to be packed tight together, minimizing air spaces. Wire used in motors and generators is generally coated in enamel to allow the windings to be packed tight together. Traditional rubber or polymer insulation would make the wire diameter thicker, this is one reason why old electric motors were bigger and heavier than modern motors of the same horsepower.

See how motor wire is packed and wound into modern induction motors in our video here.

Learn more about the whole field of electrical insulation on our page here.

Hands-on Exercise: Burn up a motor!

Have you noticed that when a toy's motor gets very hot it smells? This is the insulation vaporizing. Heat breaks down all forms of insulation eventually, and in a motor winding when the insulation gets weak enough two wires side by side will short, this causes and arc and the device burns out.

If you take a small motor that you don't care about you can intentionally burn it out to see what happens to the windings. You can do this by putting more than the recommended voltage through the device, or by running the motor hot for a long period of time. Consult with an electrician or engineer to do this exercise safely.