But who wants to do math in a trench or on a roof? Use a calculator. If you don't have a calculator handy, memorize these "Rough as guts" rules for Copper V-90HT (Standard building wire):
Next time a customer asks, "Why can't I just use 1.5mm² cable for my 200-meter driveway light?" send them here. voltage drop calculator australia
Example: A 20A circuit, 50 meters away, using 2.5mm² cable. (50 x 20 x 0.017) / 2.5 = 6.8 Volts lost. (6.8V / 230V = 2.9% drop – acceptable for general use). But who wants to do math in a trench or on a roof
Ignoring voltage drop doesn’t just make your lights dim; it burns out motors, voids warranties, and fails compliance under . 50 meters away