I'm confused by a couple of online calculators I've found.

I'm trying to determine the proper gauge wire to carry 20A, 120VAC over a
distance of 300 ft. with an approx allowable 2% (per NEC) voltage drop.
This UF cable will be buried for most of it's length.

This calculator:
http://www.stealth316.com/2-wire-resistance.htm
advises a 6 ga. wire would be sufficient (voltage drop 2.414V)

However, this calculator seems much more conservative:
http://www.vihon.com/Vihon_Calculato...alculator.html
It says a 0 (zero) gauge wire is required !

Also would like some real world advice on the voltage drop recommendations
of the NEC. At what point does one see excessive/dangerous wire heating?
2% ? 5% ? 10% ? 20% ?

-- Paul