I have a very long property with no power at the back. I'm trying to get a 13A reciprocating saw out there to do some demo work. The cable would need to be ~250'. Does the NEC have a table that would specifically address this? I found 310.15b online. It looks old and I'm not sure if it is still accurate. Also, I assume this is copper wire but I am not certain. What I concluded is 12ga @ 250', roughly 77m would have right about 0.4 ohms of resistance. Seems pretty high to me. I don't know what the standard is, but I think most of my extension cords are in the 0.15 to 0.2. If my math is correct, 10ga would drop the resistance to 0.25 ohms and 8ga would drop it to 0.16. Is this correct, or is there a more precise table for something like this?
https://i.pinimg.com/564x/55/c0/94/55c09494b62a662d1ae240a6a90cddec.jpg
Best Answer
Southwire has a voltage drop calculator here: https://www.southwire.com/calculator-vdrop The resistance for 250' of 12ga is indeed around .4 ohms.
You also should remember that you'll only be drawing 13 amps when the saw is fully loaded. According to the calculator when drawing the full 13 amps you'd see a voltage drop of almost 10% on 12 ga wire. For 10ga at full load it would be just over 5%.
Up to you if you want to save some money on wire and risk higher voltage drop or spend quite a few more bucks and get 10ga.