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Length vs. AWG vs. Ampacity: How Do These Parameters Impact Cable Choice?

A relationship between the length of the cable, its gauge, and ampacity is a common concern for our customers. Let's assess the difference between the three in simple terms.

What are length, AWG, and Ampacity? Defining The Terms

The length of the cable you buy is determined by how much cable you need to get from point A to point B. 

AWG, or American Wire Gauge, is a standard measure of cable conductor size used in the United States, North America, and some countries worldwide. A small gauge indicates a large diameter of a cable. For instance, 2 THHN THWN-2 Stranded Copper Building Wire is way larger than 14 AWG THHN THWN-2 Solid Copper Building Wire. The gauges between 2 and 14 are the most common ones on the market. When you buy a cable, you always pick a particular gauge, one accurate measure of cable size.

Amperage is the common term that indicates the strength of the electrical current. The term amperage relates to the cable circuit. However, when it comes to wire and cable, a more relevant term is ampacity, which is the highest amount of current that a wire and cable conductor can carry in the circumstances of use while sticking to its proclaimed temperature rating. The measurement of cable's ampacity is in amperes, or, shortly, amps. The sizes of ampacity are available for the electrical circuits. For instance, a typical ampacity of the electrical cable in a circuit in a private home that is used for home wiring is 20 amps, while a lighting circuit requires a lower current capacity of 15 amps.

How Are Length, AWG, and Ampacity Connected?

The more the amperage of the electrical circuit is, the higher should the ampacity of a cable be and the smaller the gauge should be. The cable should be thick enough to deal with the particular amperage so that it does not warm up to a critical temperature.

Does wire length affect amperage?

The length of the wire does not have a direct impact on amperage, but it does have an effect on voltage through resistance. The longer the wire, the higher is cable resistance and voltage drop.

Resistance is the term that indicates how the wire or cable resists the electrical current flow. Measurement of resistance impact is voltage drop, the term that indicates the decrease of the cable's electrical potential in a current. A voltage drop that is less than 3 percent is acceptable. In case the resistance from a particular cable does not impact the voltage drop for more than 3 percent, the impact of the wire length on resistance is not really significant, and the cable will work great without heating up. In some cases, you might have to use a smaller gauge than you otherwise would if the cable is too long. This relates mostly only to very long lengths of cables.

You can click on this page to calculate the voltage drop of a particular cable in a specific circuit to see if it is significant.

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Length vs. AWG vs. Ampacity: How Do These Parameters Impact Cable Choi