Page last updated
Voltage Drop Calculator
for visiting NoOutage.com to use our free voltage drop calculator.
Use this calculator to estimate cable voltage drop for sizing conductors. The calculation assumes uncoated copper or aluminum conductors operating at the temperature selected and is based on the ac/dc resistance or impedance from NEC 2011 Chapter 9, Tables 8 and 9 for stranded conductors operating on a DC or AC 60Hz system. Rather than using the 'k' factor or the 'Effective Z' of Table 9 this method is based on the actual ac resistance and reactance values from the table. The load current input is fixed, as is the base system Voltage. The Voltage drop in the cable is calculated using Ohm's Law where Vdrop = Iload x Rcable. The percent drop is Vdrop / Vsystem x 100. For ac systems the ac impedance is used in place of the dc Rcable. This methodology is similar to the examples given after NEC Table 9.
The ampacity of each conductor size shown for reference in the dropdown menu below is based on NEC 2011 Table 310.15(B)(16) for 60C insulated conductors rated 0 through 2000 volts with not more than three current carrying conductors in raceway, cable or earth with an ambient of 30°C (86°F).
Note that the actual ampacity and voltage drop for your application may differ from these results but in most cases will be very close to those shown here.
Units herein are American Wire Gauge (AWG) and English (feet).
Click here for alternate calculator that also includes a transformer and motor load.
UPDATE: On 11/4/2009 the 3-phase % calculation was adjusted by a factor of 1.732
UPDATE: On 9/25/2013 added #16 AWG; ac values extrapolated
UPDATE: On 4/27/2018 added 850V, 1000V and 1500V for dc solar systems
UPDATE: On 10/16/2018 added 70V, 80V, 90V for dc systems
UPDATE: On 02/25/2019 updated and added NEC references, expanded methodology description, added NOTE 4 and NOTE 5.
UPDATE: On 4/3/2019 added more Voltage choices between 120 and 208 for dc solar systems