A very important part of any tool’s performance is getting it enough power to run correctly however it is a consideration which is sometimes overlooked. We wanted to quickly cover some of the basics and things to consider when purchasing and/or using extensions with various power tools.
Doing the Math
The simple calculation for figuring your power needs is Watts/110 = Amps (or Amps x 110 = Watts). Each power cord will have a maximum Amperage rating which is a function of gauge thickness (thicker the cord, lower the gauge number) and length. As electricity travels the length of the cord, power is enviably lost so it is critical to always get a cord rated higher than your tool requires. Another consideration is if you use 2 or 3 cords together the Amperage rating will drop noticeably, which seems to slip people’s minds from time to time. Here is a voltage loss calculator if you want to get real scientific but that is most certainly overkill.
Examples of Tool Amperage: Oscillating Multi-Tool 2-4amps, Drills 6-10amps, Sanders 2-10amps, Grinders 7-15amps, Rotary Hammers 10-15amps, Circular Saw 13-15amp, Routers 13-15amps, Core Drills 15-20amps
Using a small Dremel or sander you will probably never see any issues with any cord but the bigger stuff is where you have to pay a little more attention. Normally 15amps will be the upper limit for most power tools because the standard US outlet is 110v rated for 15amps. Tool manufacturers will push the 15amp limit because they are all trying to make the most powerful tools possible. 
There are however 20amp outlets (5-20P), some may even be hiding in your own home disguised as 15 amp outlets, see center image above. Core Drill Rigs are one common example of 110v power tool that do require 20amps. Generators also commonly have 20 or 30 amp outlets available as well. Some power tools utilizing the 20amp power supplies may also use one of the twist lock connection extension cords and it can gets pretty messy from there. If you have questions at that point it is probably best to call the pros at Ohio Power Tool 800-242-4424, they are always happy to help.
Selecting the Right Cord
For the 10-15amp power tool used on a jobsite we definitely recommend 12ga extension cords rated for outdoor use (-40f – 140f) in either 50ft ($31, Ohio Power Tool) or 100ft ($55, Ohio Power Tool) lengths that include the lighted end. For shop use the retractable reel style extension cords in a 14ga or 12ga are very nice for organization, convenience, safety and protecting the cord. At 50ft both should still be rated at 15amps (over 50ft 14ga would drop below 15amps). More commonly however these retracts are found in 16ga (10amp, 1250watt) but since they look very industrial with 3 prong plugs sometimes this leads folks to believe they are rated for 15amp tools which is not the case.
Safety First
Underpowered extension cords are a very common occurrence because it’s a simple equation of people wanting the most powerful tools and being cheap when it’s time to buy extension cords. We have all done it but it can cause damage to the equipment and/or will cause the tool to not perform as it is specified. A ground-fault circuit interrupter GFCI ($22, Ohio Power Tool) is also a must for proper protection from electric shock of the tool but more importantly the user. For professional jobsites OHSA is very serious about correct power cord usage. They are also very serious about proper maintenance of the cords with no nicks or noticeable wear. It is however completely acceptable under OSHA rules if a cord should get damaged to cut and reattach a new connector as long as this is done correctly. Taping over a cut or splicing will not qualify as a proper repair for those guys.
