AWG Amp Carrying Capacity of Aluminum and Copper Cables
AWG stands for American Wire Gage system, which tells us about the gage of a wire. With the increase of AWG value, the wire diameter decreases. Similarly wire diameter increases with a reduction in AWG value. If the AWG of a wire is thicker than 0AWG, we don’t go toward negative digits. Instead more zeros are added and we end up on fig 00000 or 5/0AWG.Our computer and telephone lines have AWG rating in between 26-22 and the thickness of the conductor varies from 0.40mm to 0.64mm. Similarly the power line in our home has average AWG rating of 14-12. As wire thickness increases, AWG value decreases with decrease in resistance per unit length. One thing that should be kept in mind is that wire diameter is measured without insulation, i.e. it will be the diameter of the bare conductor.
Since AWG rating also affect resistance of wire, in applications like driving speakers it become very important to select the proper value AWG wire. Let say we connect a stereo sound system to a speaker via a wire having resistance not of the order needed to drive the speaker. What will happen? The stereo system is transporting audio signals in the form of electrical signals through a wire to drive the speaker, and the wire resistance is greater than that desired. The electrical signal will lose its quality as it the passes through the wire. We will get a bad sound at the output of speaker. This scenario shows how important it is to select a wire with the appropriate AWG. Wire gage plays a vital role when it comes to applications like driving speakers, electric power distribution from power plants, driving automobile starters, and networking.
Ampacity: It is the ability to wire to carry maximum current without any physical damage to a wire or its insulation. As current flows through, it heats up because of power dissipation which appear in form of I*I*R lose. The temperature of wire should not reach the limit of 80C to avoid oxidation. Major losses that occur in aluminum and copper cables include:
- I*I*R electrical losses
- Dielectric loss
- Skin effect
I*I*R losses: These losses are also called "I squared R loses" or electrical loses. They occur because a conductor offers some resistance to the flow of electrons.
Skin effect: In skin effect the current starts flowing over the surface of conductor and through the inner conductor. The effective area for flow of current is greatly reduced. So current flowing at surface of conductor has greater density than current flowing through the internal core. Skin effect is greatly dependent on frequency; it varies with an increase in frequency.
Proximity effect: This is a type of loss that occurs due to the rotation of a field. The magnetic field jumps from one conductor to the near-by one. Such losses occur due to closeness of wires, bends in wire, skin effect, and high frequency noise.
Please click the image to enlarge.