Voltage Drop Three Phase

Centigrade Fahrenheit Square Inches Circular Mils Cost kwH Circular Mils
k Constant Voltage Drop 1 Phase Voltage Drop 3 Phase Voltage Drop Percent
Voltage Drop Multiple Legs Transformers 1 Phase Transformers 3 Phase AC Refrigeration 1 Phase
AC Refrigeration 3 Phase Conversion Home Electrician Math Home Electrician Education Home

Three Phase Voltage Drop

This calculation is one which is important if a load is 208 volt and more than 150 feet from the source of power, and also important if the load is 240 volt and more than 200 feet from the course of power.

The algebra formula for voltage drop is:

Vd = (1.732 X k X I X L) divided by cm


X means times
Vd equals voltage drop in volts
1.732 is for there and back of a three phase circuit
k is the constant calculated by R times cm divided by 1000
I is the actual current the load will draw
L is the distance in feet the load is located from the source

Note: The formulas are identical for single phase and three phase voltage drop with the single exception that for single phase the factor is 2 in the formula and for three phase the factor is 1.732 or the square root of 3.

Find practice problems HERE.

Find audio support HERE.




Many electrician workbooks and practice exams are now available 
as digital downloads for immediate use. 
Click HERE to see what is available.

Products For Sale
2006-2011 David U. Larson
Companion Website to ElectricianEducation.com ,
2011NEC.com and
Other websites by David U. Larson which may be of interest: