Sign Up for the Newsletter

Extension Cords

When purchasing a Construction Grade extension cord, you should take many factors into consideration including the physical environment in which the extension cord will be used, and the total loads power (amps/watts) requirements. Construction Grade extension cords are used for greater lengths, higher amperage and voltage requirements, and require protection from the rough environmental conditions. All extension cords come with information about length, amperage ratings, voltage ratings and whether the cord is intended for outdoor use, as well as other information that the manufacture deems important.

Pretty straight-forward: buy the correct grade of extension cords and send them to the jobsite. However, just recently an electrical contractor in Indiana was told by their General Contractor that the OSHA Inspector warned them they would be fined if they plugged one extension cord into another. The inspector told them they would have to supply Spider type Power Distribution boxes within every 100’ in order for the other contractors to use a 100’ or less extension cords. They were told that the allowable fine could be up to $12,934 per violation. How can this be right? With the assistance of the Extension Cord De-Rating Amperage Table we can see the potential problems when plugging one extension cord into another.

Extension Cord De-Rating Amperage Table

Cord Length (Feet) Maximum Amps Available AWG Size
25 10 18
25 13 16
25 15 14
50 5 18
50 10 16
50 15 14
75 5 18
75 10 16
75 15 14
100 5 16
100 15 12

The longer the extension cord (voltage drop), the more resistance is offered, producing heat as a by-product. All power tools draw a given amount of current (watts/amps) to run correctly and efficiently. Some electrical loads (watts/amps) may be too great for the wire size (AWG) of extension cord it is attached to. Due to the wire size, the resistance of the wire, and the voltage drop due to the distance (x2), these variables can overheat, causing damage to both the extension cord and the power tools to which they have been connected.

An example: A 100’ #12AWG cord set is good for 15amps. If you were to plug a second 100’ #12AWG cord set into the first you would have to de-rate them to 7.5 due to the length of the two extension cords being connected. You can readily see that if you plug in three drills drawing 5amps each (3×5=15amps), you will either trip the 15amp breaker or burn out one or more of the drills and/or the extension cord. It’s not too difficult to see the problem if you were to plug a #12AWG and a #16AWG together.

Now you can confidently choose the right one by following the extension cord chart provided. Follow these simple rules when buying your next extension cord and you can send it out to the site without concern for your workers safety or OSHA fines.

Written by;

John Henle