I want to run some additioal wiring which will have an approximate home run distance back to the electrical box of 80ft. Can I still use 12/2 or 12/3 romex or do I need to use 10/2 or 10/3 because of the long distance. I will using this run for a series of high hats (approx 21 cans - figure 75watt max) I will probably put in a new breaker and I was figuring on going with a 20amp instead of a 15, I don't know if I need to go to the 20.

At 15amps going the 80ft, you should actually be running #8. The guidelines for #10 is a max of 75 ft at 15 amps.

Thanks arwoodman

That load is only 13.125 amps, you can load a 20 amp circuit to 16 amps, 15 amp to 12 amps. for the 80 ft you could use #12 wire the voltage drop is less than 5%, but you could use #10 if you would like, but do not think you will gain all that much, a little drop in voltage will make your lamps last longer

Unless my calculations are wrong I agree with Frank40