I don't get it. Whenever I look at a corded tool at amazon, I see that people are buying the tool with a cable with an incorrect gauge. Here is an example:

Mower and cable

In this example a 13A mower is "frequently bought" with a Gauge 16 cable. Gauge 16 cables are very clearly labeled as maxing out at 10A. Especially for a 100-ft long extension cord, at least a Gauge 14 cord is needed.

Are so many buyers clueless, or are the guidelines to use a Gauge 14 cable with 13A device (for a 100-ft extension) overly conservative and one can get away with a Gauge 16 cable?

  • 5
    Data talks, and the results are... people are stupid. Even some tradespeople I work with don't understand cord length/gauge issues. Oct 29, 2015 at 15:03
  • In building codes another factor is at play. Your home may be designed for five people per square yard, but the floor will not actually cave until you put ten people per square yard, and throughout a room. I am wondering if the code for electric cables is also conservative in the sense of being under-rated for safety.
    – Calaf
    Oct 29, 2015 at 15:09
  • 3
    There are two factors in play when it comes to gauge for a cable. The safety and the voltage drop. For short loads that are common on an extension cord, the cord rarely will heat up. But in the example, 13amps on 16 gauge will cause about a 9-10% voltage drop over 100 feet. This voltage drop will cause greater wear and tear on the tools causing them to fail earlier.
    – diceless
    Oct 29, 2015 at 15:19
  • Overly conservative is opinion, but of course they are conservative. As an aside, I chuckled at the thought of the general public having any knowledge of what an "amp" is outside of an advertizing buzz-word for vacuum cleaners...
    – JPhi1618
    Oct 29, 2015 at 15:35
  • 3
    Most consumers don't have any; or very limited, knowledge about wire gauge. Most folks think an extension cord is and extension cord, therefore a low cost extension cord seems like a good deal.
    – Tester101
    Oct 29, 2015 at 15:41

2 Answers 2


Many buyers clueless. Guidelines for extension cord wire size are only adequate for connected equipment and not conservative.

With an undersized cord for the load:

(1) The voltage supplied to a motor will be more than 10% below nominal, causing motor overheating and premature winding failure;

(2) The cord will run hot causing the cord insulation to fail prematurely;

(3) The manufacturer warranties of both equipment and cord will be void (if they know what happened);

However, if the utility supplies voltage at the high end of nominal (122v) and the mower is never used to cut thick grass then one will probably get away with using a #16 cord. The #16 cord is cheaper and less weight to haul around in the yard. Besides, someone is probably going to accidentally drive the mower over the cord in a couple of months chopping the cord to little bits...

  • It's your very last sentence that made me, despite already now owning a 12-gauge 100-foot extension, go with a rechargeable mower. Only 25% of the charge was depleted after going over both front and back yards. The noise level was low (beating 120V) and the air remained pristine with a pleasant aroma of cut grass (beating gas). Using an extension cord on a leaf blower is not too bad, because one doesn't have to be right where the leaves are. But with a lawn mower one must be right at every spot that needs work.
    – Calaf
    Dec 27, 2015 at 18:57

NEC 2014 table 400.5 (A1)

16 Awg SJ two conductor cable is rated up to 13 Amps.

SJ cord type cables @ 16 awg is the primary cable of choice used for vacuum cleaners and other popular electronic gadgets as it is lightweight and easy to manage.

Edit in regards to voltage drop:

Care should be taken when using #16 awg extension cords. If the appliance actually consumes 13 Amps continuously, it would be wise to use a larger, and shorter extension like 12 Awg 50'

Voltage drop out of the nominal recommended voltage of the appliance will make the motor work harder to perform.


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