Cord Length vs. Amperage

The thicker the cord, the higher its maximum amperage capacity.

The longer the cord, the more resistance, and the greater the loss in amperage efficiency.

While the specifics of electrical resistance and impedance are different from hydraulic resistance, ampacity can be thought of as a lot like water pressure. Just like your garden hose loses pressure over longer distances, so too ampacity is affected by cord length. This analogy helps to understand how electrical properties change over distance, similar to everyday experiences with water pressure.

In fact, Underwriter Laboratories (UL), a safety certification company, takes cord length into consideration when rating cords, and cords that are greater than 50 feet are rated for a lower amperage than their shorter counterparts. For example, an 18 gauge wire single phase 120V cord is rated for 10 amps, but when it exceeds 50 feet, the UL amperage rating drops to 7 amps. This is important to know when your device requires a specific amperage. If the distance is greater than 50 feet, you may need to opt for a thicker cord.

See the table below for a quick reference for 120V single phase cords. (See our UL Ampacity Reference Chart for more info.)

So what does this mean if you need to run cord greater than 100 feet? Well, it means there will be a further decrease in amperage. In fact, UL requires a special investigations evaluation in order to list a cord that is greater than 100 feet. So unless UL examines the particulars of your application, cords over 100 feet are not UL listed.

Choosing the correct cord ensures not only the efficiency of your device but also adheres to safety standards, preventing potential hazards. To choose the correct cord for your needs, visit our UL Ampacity Reference Chart for complete information, or reach out to our experts at sales@stayonline.com